Evolution of 8088 PCs

From the first IBM PCs, there was a steady stream of innovation and improvements to PC compatible computers using an 8088 CPU.  However, there were also some bumps along the way.  In this entry, I will try to identify many of the positive and negative features of the main 8088 members of the IBM PC and Tandy 1000 families.

1.  IBM PC Model 5150 First Version

IBM PC BIOS 1st & 2nd Revision - The original PC BIOS was the byword for compatibility.  

Chassis - two full height drive bays, unique system board mounting, 13" maximum expansion board length, PC cone speaker.  

System Board & Expansion Cards - Use of off the shelf components or TTL logic chips, configuration by two rows of dipswitches.

Power Supply - The form factor would be the same for the IBM PC/XT and this established a standard "AT Power Connector", passthrough port for monochrome monitor

Expansion Slots - The 8-bit PC or XT slot was introduced.  Five slots were better than most other home computers at the time.  However, the floppy disk controller, the video card and memory cards each took up a slot, so expansion was limited.  

Cassette Interface - Important for saving programs in Cassette BASIC, used in Music Construction Set.  5-pin DIN connector, used TRS-80 cassette cables

Diskette Drive Adapter - Standard equipment, supports all double density drives, 34-pin card edge connector.

Diskette Drive (Single Sided) - Tandon TM100-1s were used in the beginning, supporting 160KB or 180KB per side.  4-pin molex connector used.

System Board Memory - 16-64KB on the motherboard, 16KB minimum, expandable to 544KB via expansion slot memory upgrades, first bank soldered, remaining three banks socketed.

System ROM - 6 x 8KB sockets, five used for BASIC and BIOS.  Empty socket, but requires an adapter for EPROMs.

IBM PC-DOS 1.0 - Included Disk BASIC and Advanced BASIC, loads COMMAND.COM, IBMIO.COM and IBMDOS.COM.  

Asychronous Communications Adapter - 8250B UART serial port, switchable between COM1 and COM2, DB-25 male connector.  Most can work in XT Slot 8.

Printer Adapter - Printer port, 378H (or 278H with modification), DB-25 connector female connector

Game Control Adapter - DA-15 female connector, joystick support (third party), four axes and four buttons.

Monochrome Display and Printer Adapter - DE-9 female display connector, 80-column text, 9x14 character cell, TTL monochrome displays only

IBM PC Display Model 5151 - Display for the above adapter and later Hercules Graphics Card, powered through PC power supply, long persistence phosphor, monochrome green screen, brightness and contrast controls.

Color/Graphics Adapter - CGA, 16 colors selectable, 4-color palettes, 40 & 80 column text mode, composite color output, artifact color, 320x200 and 640x200 graphics modes, RCA composite video jack, light pen support, RF switchbox (third party) support

Math Coprocessor - Unidentified at first, empty 40-pin socket for 8087 upgrade.  

IBM PC Keyboard - 83-key first standard keyboard, Function keys on side, buckling spring technology, 5-pin DIN connector

IBM Graphics Printer Model 5152 - Epson MX-80 clone, parallel printer, dot matrix printer

2.  IBM PC Second Version

IBM PC BIOS 3rd Revision - Fixed bugs, added support for 640KB of memory, bootable option ROMs

IBM PC-DOS 1.1 - Double sided disk drive support, used Tandon TM100-2As.

Double sided disk drives - 320K and 360K per disk supported

System Board Memory - 64KB to 256KB on system board, now expandable to 640KB via expansion slot upgrades

Bootable ROM - Devices can have a boot ROM and the BIOS will allow the device to install its own boot handler, booting directly to a hard drive now possible.  EGA and VGA support possible.

3.  IBM PC/XT Model 5160

System Board - Configuration now only by one bank of dipswitches.  Memory autodetected, tested and counted at bootup.  Faster bootup compared with PC.

Cassette Interface - Eliminated, making Cassette BASIC vestigial for programs that require it

IBM PC Color Display Model 5153 - Official CGA monitor (.31 dot pitch), 16 color support (intensity bit not properly supported on some third party monitors), color #6 brown, 14/13" viewable screen, vertical hold and size controls.  

IBM Expansion Unit Model 5161 - Adds seven more ISA slots, and official method to add hard disk drive to PC (whose power supply was not considered to output sufficient power to supply hard drive requirements)

IBM Graphics Printer Model 2 - Printer capable of supporting all IBM Extended ASCII characters.  Earlier printer did not.

Expansion Slots - Standard 8 expansion slots, distance between slots standardized for what would become known as ISA slots.  Slot 8 is on custom bus and only works with special cards (like the Async card).  Only 6 slots can support full length cards due to the case.  

Revised Expansion Card Brackets - Early PC brackets are black and color and are wider than later silver brackets.  This can be a problem using cards side by side in later systems.

Power Supply - 130W, sufficient to support a hard drive and more

Fixed Disk Adapter - Built around Xebec chips, standardized XT hard drive controllers, including XT-IDE drives, supports two MFM drives, slow 6:1 interleave.    

Fixed Disk - 10MB Seagate ST-412, Cylinder/Head/Sector addressing, MFM, Full Height.

System Board Memory - Same four banks as IBM PC, but all four banks socketed

IBM PC-DOS 2.0 - 9 sector floppy disks supported for 180KB per side or 360KB per disk, device driver support, revised file handling system, hard disk support (15MB maximum)

ROM Sockets - Support Standard 32KB EPROMS for 64KB ROM (only 40KB used on XT first BIOS)

Secret Memory Expansion - By adding a 74LS158 chip to socket U84, jumpering E2 and replacing the 64Kx1 RAM chips in banks 0 and 1 with 256Kx1 chips, you can have 640KB on the motherboard.  Later XTs come with the mod.

4.  IBM PC Portable

Composite Monochrome Monitor - 5" amber screen, composite connection to CGA card

Half-Height Diskette Drive - Two supported

Portability - For 1983, this meant a sturdy handle, a slightly modified keyboard that could attach to the chassis, and a power plug.  System weighed almost 40 pounds.  Only two full length cards supported

5.  IBM PCjr. Model 4860

Cartridge Slots - For games and software, up to 64KB for each cartridge, two supported.  Also used for Cartridge BASIC.  Only appears on PCjr. and JX.  

Sidecar Expansion Bus - Attach expansion boards without having to open computer, including parallel port and memory expansions.  It lengthens the physical footprint of the system.

Cordless Keyboard - IR keyboard powered by 4xAA batteries and allowing for cordless operation 20-feet away, line of sight must be maintained, keyboard cord optional.  

Internal Modem - 300 baud Novation non-Hayes compatible modem.  Special internal slot connector, standard RJ-45 port.

System Board Memory - 64KB on motherboard, 64KB via internal expansion card, up to 736KB total via sidecar.  System designed for 128KB, program must support extra RAM (Flight Simulator 2.0) or DOS must have a device driver to load more RAM

Enhanced CGA - Adds 160x200x16, 320x200x16 and 640x200x4 modes, but only BIOS level CGA compatibility

IBM PCjr. 3-Voice Sound - 3 square wave channels plus noise, 11-bit frequency selection, 4-bit volume control per channel, periodic and white noise selectable at four frequencies.  Requires external speaker of some kind

System Configuration - Totally jumperless and dipswitchless, internal expansion cards and external IBM expansions automatically detected, memory detected (up to 640KB) and configured via software

Diskette Drive Controller - Only one drive supported, accessed at different ports, uses 34-pin header

Proprietary Expansion - External ports use unique BERG connectors.  

Cassette Interface - Last PC compatible system to include a cassette interface.  Only official IBM cassette cable is for the PCjr.

TV Connector - Only official IBM RF switchbox is for the PCjr.

Joysticks - Gameport on systemboard, supports two joysticks without a y-adapter.  Only official IBM Joystick of the PC line is for the PCjr.  Joysticks function the same as PC joysticks, just have a different connector.

Serial Port - Includes 8250B Serial Port, official IBM DB-25 adapter available.  Uses COM2 resources, 278H/03I, but BIOS calls it COM1 if internal modem is not installed.

Power & Cooling - 33W power card came first, followed by 45W card.  45W sufficient to power three sidecars.  Only system here able to be run silently without risking overheating the power supply since the fan cools the disk inside the disk drive.  

IBM PCjr. Color Display Model 4863 - Higher dot pitch (.42) than the PC Color Display, but also includes a speaker and uses the PCjr. video connector.

IBM Compact Printer - IBM's official serial printer, uses PCjr. serial connector, can use an adapter for any serial port, low cost thermal printer, surprisingly decent.  

IBM PCjr. Speech Attachment - IBM's implementation of TI's Speak and Spell technology and more. Built in vocabulary.  Capable of recording and playback of digitized sound.  Later emulated by many devices.  

Compatibility - Compatible with most IBM software, but notable exceptions include Microsoft Decathalon, 101 Monochrome Mazes and Microsoft Flight Simulator 1.x.  Usually not so compatible with 3rd party software not written to take the PCjr. into consideration.  

IBM PC-DOS 2.1 - Adds full BASIC support for PCjr's advanced graphics and sound, but requires Cartridge BASIC to work at all.

6.  Tandy 1000 Model 25-1000

Expansion Slots - 3 standard XT slots, but only 10" cards or shorter supported

PCjr. Features - Brought over the Enhanced CGA and 3-Voice sound from the PCjr.

Compatibility Improvements - Unlike the PCjr., the Tandy 1000 could run most PC software that accessed the hardware directly.  

Tandy 1000 Keyboard - 90 keys, including separate cursor keys and F11 and F12 keys, but support for these keys was hit or miss.  

DMA & Memory Upgrades - Upgradeable to 384KB and DMA with one Board, 640KB with a second board.  Full DMA support compared to PCjr (which only allowed DMA for floppy, and available via 3rd party upgrades only)

Printer Port - Built in, but limited and uses card edge connector

Power Supply - 54W, considered adequate for two drives and three expansion cards

Tandy CM-2 High Resolution RGBI Color Monitor - Later known as the CM-10 and CM-11, this was the Tandy equilavent of the IBM PC Color Display, although the dot pitch (.43) is not quite as sharp as IBM's (.31)

Tandy MS-DOS 2.11 - GW-BASIC supports enhanced graphics and sound of the Tandy 1000s, no FDISK to partition hard drive.

7.  Tandy 1000A Model 25-1000A

Coprocessor - Adds 8087 Math Coprocessor Support

286 Express Upgrade - Compatible without special daughter board the plain 1000 requires.

8.  Tandy 1000HD Model 25-1000HD

Fixed Disk Drive - 10MB half-height model and Xebec controller that could use IRQ2.  IRQ5 is standard on XTs, but the Tandy uses it for a vertical retrace interrupt.

DMA & Memory - Came with one board that gave DMA and allowed you to upgrade to 640KB with one board, also supplied a PLUS connector (see below) to add another expansion device like a serial card without taking up another slot.  

Tandy CM-4 RGBI Color Monitor - Low cost RGBI monitor with a large dot pitch (.62).  Not recommended for 640x200 graphics.  

9.  IBM PC/XT Revised

101-Key Keyboard - IBM made Model M keyboards work quite reliably on an XT with 2nd and 3rd BIOS.  On a first BIOS XT or any PC, the odds are much lower that it will work at all.

Improved Drive Support - BIOS support in 2nd and 3rd BIOS for 3.5" double density and 5.25" high density drives, but a third party floppy controller is required for the latter.  

System Board Memory - Supports 640KB on the motherboard without modification.

Mounting Hardware - IBM supplied late XTs in a dual half-height floppy configuration and included mounting hardware to fit them inside a full height bay.  

10.  IBM PC Convertible Model 5140

LCD Display - Simulates something like a 2-color CGA display, but in 320x200 (stretched to double width) can manage four intensities of color.  Also can emulate the MDA.  

Diskette Drives - IBM's introduction of 3.5" double density disk drives.  Would take until the PS/2 for 3.5" disks to fully catch on.  

Keyboard - 78 key keyboard, functions similar to PCjr. keyboard but improved by using IRQ1 for keyboard interrupt and not using CPU to deserialize scancodes.  

Internal Modem - Slot inside for 1200 baud version of PCjr. modem, may or may not be Hayes compatible.

Expansion Bus - XT bus with multiplexed address and data lines.  

Battery Operation - Uses CMOS 8088 CPU, SRAM to save power and allow for battery operation, system can be suspended indefinitely.   

Attachable Printer - Thermal printer, more advanced than PC Compact Printer.

Display Slice - Provides full CGA compatibility to external RGBI monitor.  Connector supports IBM PCjr. Display or IBM PC Convertible Color Display Model 5145.  RCA jack can be used with color composite monitor.  IBM also introduced the 9" IBM PC Convertible Monochrome Display with green phosphor.  

Portability - Although still large and bulky by modern standards, this is a true laptop.

Convertibility - Can remove LCD to place unit underneath standalone monitor.  

11.  Tandy 1000 EX Model 25-1050

Dual Speed CPU - 7.16MHz/4.77MHz, selectable at bootup or via Tandy MS-DOS Mode command.

Slimline - Takes up less desk space and the keyboard is built into the system unit just like an Apple IIc.  (Does not apply to SX) 

Selectable Boot Drive - You could boot to the internal 5.25" floppy drive on an external 3.5" floppy drive 

Expansion Bus - Uses a 62-pin version of the XT expansion bus, cards (called PLUS cards) stack onto each other, but must be short.  (Does not apply to SX)

DMA and RAM Expansion - One PLUS card upgrades system to DMA and allows for 640KB

External Drive Connector - For connecting a second 5.25" floppy drive or a 3.5" floppy drive

Earphone Connector and Volume control - When you want a quiet PC (not on SX)

12.  Tandy 1000 SX Model 25-1051, 1052, 1054

Dual Floppy Drives - 2x360KB Floppy drives on Model 25-1051 and 1054, boot floppy can be selected on bootup.

Expansion Slots - Five expansion slots provided without any need for memory expansion

Memory Expansion - Upgrade from 384KB to 640KB with 8 x 256Kx1 chips

DMA - Included on all machines (optional on EX and HX)

286 Express - Official 286 speed upgrade, 8KB cache that can be disabled, supports 80287 coprocessor.  Software controlled. 8088 still available for programs that will not run on a 286 or on the faster speed

Tandy MS-DOS 3.2 - Supports 3.5" drives, FDISK partitioning, 3 extra 32MB DOS partitions using MLPART (non-standard)

Power Supply - 65W, considered adequate for two drives and five expansion cards

13.  Tandy 1000 HX Model 25-1053 (all the EX features plus) :

Boot Speed and Menu - Nearly instant boot to an optional menu where you can select the boot device (floppy, DOS, Deskmate)

EEPROM - Save settings permanently without dipswitches or jumpers.

DOS-in-ROM - Enough DOS 2.11 is on the system that you will not usually need to insert a DOS disk when loading programs off floppies.  Disabled if a hard drive is installed.  Also supports 3.5" disk drives natively, which regular DOS 2.11 cannot.

Power-in-drive cable - No separate molex or mini-molex connector required.  A headache for wanting to use standard drives.

IBM PCjr. Exclusive Games - ScubaVenture & Mouser

The IBM PCjr. had eight cartridge games, and of them, two are exclusive to the system.  They don't exist for anything other than a PCjr. and since they came on cartridges, they are not designed to work with any other computer.  These games are ScubaVenture and Mouser.

ScubaVenture and Mouser, both programmed by Nasir Gebelli, are very minimalist, enigmatic games.  As Gebelli only had 8,192 bytes to fit the program in (they use 8KB cartridges), you can understand why they lack anything beyond the minimum necessary to make playable games.

Gebelli himself is something of an enigma, as he began programming games for the Apple II, then he did these PCjr. games and some years later worked for Square in Japan programming Rad Racer, Final Fantasy 1-3 and Secret of Mana.  Thereafter, he quit video games altogether and has not returned to them, despite his obvious talents.

Gebelli's PCjr. games lack polish, which is very unusual as IBM released them and shipped them on expensive cartridges.  ScubaVenture has some very impressive smooth vertical scrolling and supports two player simultaneous play.  Mouser is more of a puzzle game requiring a fair bit of strategy.  Both use the PCjr.'s 160x200x16c mode for colorful low resolution graphics and 3-voice sound.

Common Controls

Press F1 for one player and F2 for two player (That is Fn and 1 or 2 on the PCjr. keyboard).  If left untouched, the programs will enter a demo mode.  Both games use the keyboard by default.  They can use joysticks by pressing the J key on the keyboard.   You can return to the keyboard by pressing the K key on the keyboard.  Press Esc to pause.  Each uses the cursor control keys and the spacebar or the joystick positions and button 1 on the joystick.  When your game is over, you will not be returned to the title screen, so press F1 or F2 to start a new game.

ScubaVenture

Title Screen

The object of ScubaVenture is to collect treasures while swimming to avoid the eel on the bottom of the screen.  If you touch the eel, you are stuck on the bottom of the screen.  Press spacebar/button1 to launch a new diver.  Once your third diver is eaten, the game is over.

Divers, Eel, Score, Fish

You will come across yellow keys, each looking different.  Touch the key to take it, and if you touch another key, you will take that.  Soon you will see some "treasure boxes", and each corresponds to the shape of one key.  If you touch the box with the right key, you will earn points.  You will also earn points if you touch the red fish.  Obstacles include seaweed, seahorses and the yellow "walls" on the sides of the screen.  If you touch one of these obstacles, you will not be able to move forward and must try to find a way to move around or you will be eaten by the eel.  In the one player game, a white diver will randomly swim across the screen and can block you and can take fish.  He can swim through the yellow walls and the eel will not eat him.

Keys and more Keys

Eventually, the tunnel will loop around.  This will allow you to try to obtain a(nother) treasure.  The cavern will loop until you have obtained all the treasures or have lost all your lives.  Once you have obtained all the treasures, you will move onto a different tunnel.  

Treasure Boxes

In the two player game, each player will have three divers and compete on points.  If you are using the keyboard, player one will use the regular keys and player two will use the AWSZ to move Left, Up, Right and Down.  The Tab key will release another diver for player two.  Player one's divers wear a green suit, player two's divers wear a red suit.  When one player loses all of his divers, his diver will turn white and move randomly, just like the one player game.

Obstacles

Starting the game is a bit confusing.  When you press F1 or F2, the title screen will seem to reset itself.  If you keep pressing F1 or F2, the title screen will continue to reset.  Let the music play until the ScubaVenture and NASIR text begin to flash.  When that is finished, the game will start.

More Obstacles

Two Player Mode

Mouser

Title Screen

The object of Mouser is to trap all the mice in each of the nine rooms.  In each room there are walls that you can push clockwise or counterclockwise.  The nine rooms are laid out in a 3x3 arrangement, and you can exit the rooms using the passages indicated.  Each room is laid out in a 9x5 grid.

Starting Out

To trap a mouse, you must box it in on all four sides by walls.  You cannot leave it any space to move.  If you trap a mouse, the cat will eat it when you leave the screen.  The cats are useless otherwise.  If the mouse can move a square, then he isn't trapped.  If one of the sides of the trap is the cat, the mouse will not be eaten when you leave the screen and you can't win the game.  If you trap a mouse, a special sound will be heard and you will receive the points for trapping a mouse.  Sometimes you will enter a screen and the mouse will already be trapped and you earn the points automatically.  The time will also be reset.

I trapped a mouse!

To push a wall clockwise around a pivot, walk into it.  To push a wall counterclockwise, push the spacebar/button 1 as you walk into it.  The wall will turn 90 degrees on the pivot, and you can use the directions to move the walls to where you need them in the room.  If you push one wall onto another, the wall will turn white and the next time you push that wall, one of the walls will be pushed forward in that direction one space.  You cannot push a wall if it would go through a space occupied by a mouse, a cat, the cheese or a wall. Nor can you push a white wall onto a white wall.  Sometimes when pushing a wall, there is some residue of it left behind, enough to block your character from that direction, but the mice can chew their way through it.

The Flashlight

In some rooms, there are pieces of cheese.  If a male (light red) mouse touches the cheese, he will eat it and the cheese will appear elsewhere on the screen.  If a female (light magenta) mouse eats the cheese, it will spawn another male mouse.  Male mice are stupid and walk back and forth in a pattern, but female mice can walk in a much less restricted fashion and are more likely to chase the player.

Dark Rooms and a Female Mouse

Some rooms are dark and require a flashlight to illuminate.  You can find a flashlight in one of the rooms.  The flashlight will only illuminate a circular space around the character, but as you enter and leave the room you can see the full layout for a second.

Two players alternate in trying to clear their rooms.  If the player touches a mouse or runs out of time, he loses a life.  Each player has three lives and the rooms are supposedly randomized every time the system boots the cartridge.  When you start a new game, the same room layouts are used.

Conclusion

ScubaVenture was probably intended for younger players, as the game is much more simple than Mouser. While River Raid probably influenced the game's development, it quickly becomes repetitive in a way that River Raid does not. Each time you complete a section in River Raid, a new section appears.  In ScubaVenture, each time you complete the section, the same section appears until you get all the treasures.

Mouser reminds me of Clu Clu Land for the NES, although Mouser came first.  It is a very frustrating game due to the way the game moves the walls.  You have to think about the direction the wall moves and hope you actually get it to move in the direction you want.  The mice always seem to move in a pattern just one square away from being trapped.  The timer runs down very quickly while you painstakingly try to manipulate the mice into your traps.  Mouser is also buggy in that you can die upon entering a screen where a mouse happens to be in the same place as the entrance.

Influences of the PCjr. - the IBM PC Convertible

The IBM PC Convertible, Model 5140, was IBM's first attempt at a battery-powered laptop.  Of course, it was thick, had a small screen, and expansions made it longer.  However, it does share more than a few similarities with an earlier of the PC family, the IBM PCjr.  While it took ideas from the PCjr. and improved on them in many respects, the system was not a great success due to its own issues, namely its high price and less-than impressive specifications compared with competitor's products of the time.  The introduction of the 3.5" disk drive on this system, when all software had previously been released on 5.25" disks, meant that it took time for the market to release PC compatible software for the machine.  Also, if the chicklet keyboard was the Achilles Heel of the PCjr, the Convertible's initial low-contrast LCD gave it a bad reputation.  Later machines used a super twist LCD and a backlit LCD, both offering much improved readability, but like the PCjr., it was too little, too late.

Keyboard - The original IBM PC Keyboard used 83 keys.  The PCjr. Cordless Keyboards use 62 keys and the PC Convertible uses 78 keys (U.S. style).  The fewer keys make handling these keyboards with low-level routines quite different from the IBM PC keyboard.  Both the PC Convertible and the PCjr. use the Non-Maskable Interrupt to generate IBM PC Keyboard compatible scan codes.

In an IBM PC, serial data from the keyboard is sent to the system unit, deserialized by a shift register and then placed in I/O port 60, the 8255 PPI Port A0.  IRQ1 is used to signal the CPU that there is a key to be read.  A program can read the raw scancode directly or execute INT 09H/INT16H to obtain an extended ASCII scancode.

In the IBM PCjr., serial data sent from the keyboard is sent to bit 6 of I/O Port 62, 8255 PPI Port C0.   The NMI is generated to alter the CPU that there is a key to be serviced and the CPU deserializes the data stream, then INT 48H is executed to translate the raw scancode into codes compatible with INT 09H/INT16H.  IRQ1 is never used, but the translated scancodes appear at I/O port 60.

In the PC Convertible, the raw scancode is placed in I/O Port 07D.  An NMI is generated and the NMI handler will translate the raw scancode into a compatible scancode and stores the result in I/O Port 60 and generates IRQ1 and the key can be read with INT 09H/INT16H.  While obviously derived from the PCjr., this is an obvious improvement over the PCjr.'s slow routine and should be much more compatible with programs expecting PC keyboard handling.

Memory Expansion - Neither the PC Convertible nor the PCjr. were intended by IBM to reach 640KB, both were intended to max out with 512KB.  Memory expansions for both machines came in 128KB.  IBM officially only supported the Memory Expansions for the PCjr. (128KB in system unit + 3 x 128KB expansions), but the fourth expansion was easy enough to add.  IBM only physically supported four memory modules in the PC Convertible, each with 128KB, and the system always came with two installed from the factory.  Third party expansions were required for the PC Convertible to reach 640KB and recommended for the PCjr. to reach 640KB.

Feature Expansion - Both machines were expanded by hardware attachments, the PCjr. via sidecars that fit onto a connector on the right side of the machine, the PC Convertible by a connector on the rear of the machine.  IBM released five PCjr. attachment options, parallel, power, memory, speech and cluster, and four for the PC Convertible, serial/parallel, CRT display, speech and portable printer.  If customers did not particularly care for adding onto the length of the PCjr. they must have positively detested the added weight and length that the add-ons for the Convertible added.

Modem - IBM included a modem slot in the PCjr.  It sold a modem based on the Novation Smart 103 modem for the PCjr, which could run at 110 or 300 baud.  It did not sell well because it was not Hayes compatible.  IBM also included an internal modem socket in the PC Convertible.  Apparently ignoring the market again, IBM used the same style of modem for the PC Convertible internal modem upgrade.  This time the modem could also support 1200 baud.

The COM ports were similarly assigned on both systems.  The PCjr. had a serial port built in and it was assigned to COM1, but the resources were at 278/03.  Once the modem was installed, the serial port became COM2 and the modem COM1 at 3F8/04.  The PC Convertible Internal Modem always used 3F8/04 and would be assigned to COM1 when it was installed.  This time, IBM knew enough that not everyone would install the internal modem, so the PC Convertible had a serial adapter that could be set to COM1 3F8/04 if no internal modem was installed or COM2 2F8/03 if it was

CGA Support - The PCjr. had only basic, BIOS CGA support since it did not implement the crucial Color Select and Mode Control registers.  Although the PC Convertible uses a CGA-friendly 640x200 LCD resolution, the built in video is not particularly CGA compatible either.  Color text-mode attributes were not supported on the monochromeLCD, it was either normal video, reverse video or no display.  320x200 graphics would display three shades of gray plus black, but the graphics take up the whole screen, meaning they are twice as wide as they should be.   The built in LCD does not distinguish between 640x200 and 320x200 in this instance.  The MC6845 was only emulated enough for the basic modes, the color select register is not present and the mode control register has missing bits compared to real CGA.

The built-in display adapter can also be configured to emulate a MDA card.  When the CRT Display adapter is attached to the PC Convertible, it will function like an MDA card and the CRT Display adapter should provide 100% CGA compatibility.  The Display adapter has three video output ports, a Direct Drive port using an 18-pin BERG connector with pinouts identical to the PCjr's Direct Drive video port (except no audio).  The adapter can connect directly to the PCjr. Color Display, Model 4863 or the PC Convertible Color Display, Model 5145.  It can connect to an IBM PC Color Display, Model 5153 or IBM PC Enhanced Color Display, Model 5154 or any other compatible display via the PCjr. 18-BERG to 9-pin DE-9 adapter.  It also has a composite video output like the PCjr. and a 6-pin BERG connector for an RF adapter.  The BERG connector has a compatible pinout with the PCjr. RF switch.

Printer - Both systems had a printer designed specifically for it, the IBM PC Compact Printer for the PCjr. and the IBM Portable Printer for the PC Convertible.  Both are unidirectional thermal serial printers operating at a maximum of 1200 baud and have a 2K buffer.  Both use a transmission format of 1 start bit, 8 data bits and 2 stop bits.  The Convertible's character set includes text-drawing characters at ASCII 176-223 which the Compact Printer does not.  The PC Compact Printer can print in standard, condensed, double-wide and underline styles and 480-bit graphics, while the Portable Printer adds emphasized, superscript and subscript styles and 960 and 1920 bit graphic modes.  The Portable Printer supports virtually all the control codes of the Compact Printer plus some more for its enhanced features.

Speech Attachment - The Convertible's Speech Attachment is supposed to be functionally identical to the PCjr's.

Introduction to the PCjr., or How NOT to Destroy It!

IBM PCjr. Startup Screen - Maximum RAM Count (but you can have more)

Congratulations!  You have just won a PCjr off ebay, scored one off craigslist, took one from the recycling center or was given one by Uncle and Aunt Lots-o'-Stuff in the Attic.  Its just arrived, you open the box, unwrap all the pieces, now what do you do with it?

First Things First : To use a PCjr., you need, at a minimum the system unit, the keyboard and the power cable.  If you are missing any one of these three, the PCjr. is useless.  I am going to go through each in terms of simple to complex :

The External Power Adapter: This is a large black power converter.  It has wires on either end.  One the end of one wire is a three-pronged plug.  On the other end is a rectangular three pin connector that connects to the back of the system unit.  The port is in between the A and the C ports.  On early bricks, the cable with the three-pronged plug is detachable from the large brick.  A standard three-pronged computer power cable should fit into the brick.  The brick only supports 120v/60Hz AC power, so in Europe you will need a step-down converter.  It outputs AC power, the AC to DC conversion is done inside the system unit.  The power cable can fit into the system either way (polarity is irrelevant for AC).

The Cordless Keyboard : The original Cordless Keyboard, later known by everybody, even IBM as the "chicklet" keyboard is the less common of the two IBM PCjr. Cordless Keyboards, especially after IBM offered a free trade in to the non-chicklet keyboard.  IBM called the replacement keyboard the "Freeboard", presumably because it offered some freedom from the frustration of the chicklet and was a free replacement for PCjr. owners who hated the chicklet keyboard.  Internally, they function identically.

The PCjr. Cordless Keyboards use rubber-dome technology and can feel stiff yet squishy.  The keyboard communicates with the system via an infrared sensor or via an optional keyboard cable.  It takes 4 x AA batteries, and you should check the battery compartment to see if there are old corroded batteries.  If there are, you should clean the contacts with cotton swabs or Q-tips with apple cider vinegar or lemon juice and follow it up with baking soda.  You may need to unscrew the board to inspect for leakage on the PCB.  The infrared can work up to twenty feet away according to IBM, but line of sight must be maintained and the sensor on the keyboard should be as perpendicular as possible to the sensor on the computer.  Rechargeable batteries may or may not provide reliable power for the keyboard.

The System Unit : The computer is inside on a large system board.  Most PCjr's you will find these days are the Enhanced Model, which come with a 5.25" diskette (floppy disk) drive and a 64KB memory expansion.  These have 128KB of RAM total, not counting any extra memory added via sidecar.  The Basic Model did not come with a diskette drive or the 64KB memory expansion.  If you are getting a boxed unit, it should come with all the above and two books, the first being the PCjr. Guide to Operations and the second being the "Hands On BASIC for the IBM PCjr."  A complete unit should also come with a plastic plate to cover the sidecar expansion and a Basic Model also comes with a plastic cutout to cover the floppy bay hole.

Checking for damage : The expansion ports on the rear of the PCjr. use BERG-style connectors, which little more than pins bent at right angles sticking out from the system board.  These are more prone to damage than connectors set in a D-shell, but it was cheaper for IBM to implement them in this way.  Check for any bent, broken or pushed in pins.  Most of the connectors have a missing "key pin", so check below to discover pins that are supposed to be missing.  Gently straighten or pull out any pins with a small pair of pliers or tweezers.  Expansion cables are held in the port by friction alone, so do not try yanking cables out. Similarly, the sidecar expansion port also uses pins, but at least these are cased in a plastic connector like an IDE port.

Opening the case : The case top is held down by friction and tabs, there are no screws to deal with.  Using a small screwdriver, insert it into each of the three indentations at top rear edge and gently pop that portion of the case off.

Inside the case : There are up to four internal expansion boards.  Fortunately each can only fit one way.  There are no jumpers or dipswitches inside or on the internal expansion board.  IBM did not use jumpers (officially) on its sidecar expansion board either.  Everything is configured in software, which was rather progressive for the time and technology.  If you want a true definition of plug and play, here it is!

On the left side of the unit (with the cartridge ports facing you), is the power board, which is always present.  The power board comes in either a 33W short card or a 45W long card.  If the power card is about 2/3rds the length of the case, it is the short card.  If it extends nearly to the front of the case, it is the long card.  There is a 2-pin staking connector which the power board must be inserted into when it is put back in its slot.  There are grooves in the case to stabilize the card, make sure the card fits into them.

The second board is the 64KB Memory and Display Option.  As its name suggests, this adds 64KB to the 64KB on the motherboard for a total of 128KB inside the System Unit.  Early memory boards are covered in a metal shield, later boards are just a bare PCB.  If this board is not present, you will only have 64KB of RAM in the system and a big hole if any sidecar memory expansions exist.

The third board is the PCjr. Internal Modem Option, and as it was always an optional upgrade, it probably won't be present in your average PCjr. System Unit.  IBM's modem was not very popular since it only communicated at 300 baud and did not use the industry standard Hayes command set.  Third party Hayes-compatible modems were also made to fit in this slot.  Like the power board, this card connects to a 2-pin staking connector and grooves in addition to its slot.  This is the only internal upgrade not to come automatically bundled with the PCjr. System Unit.

The fourth board is the PCjr. Diskette Adapter.  This connects to the Diskette Drive via a 34-pin ribbon cable with a pin header on one end and a card edge connector on the other.  It only supports the one internal drive.  Note the side of the cable with the colored wire, that side must correspond to pin 1 on the board if the diskette drive is going to work properly.  Pin 5 is missing on the adapter pin header as a key pin to prevent wrongful insertion.

The diskette drive is mounted on a unique plastic drive support.  It is connected to the board by two standoffs that push through the bottom of the case.  To remove the drive support mechanism (and the drive itself), first unplug the cables for the diskette drive power connector and the fan power connector from the power board.  Next, disconnect the drive data cable.  Next, with a pair of pliers, squeeze the tabs in and push upwards on the standoffs until the constrict and pop up from the bottom of the case.  These are not screws, so do not twist a screwdriver in them.  Finally, pull up on the back of the diskette drive and it should be able to be lifted out of the system with no further difficulty.

If you have removed all the internal boards and the diskette drive support, you will have complete access to the interior of the PCjr.  Check for any signs of damage and be prepared to dust.  There is a raised metal box on a small PCB, that is the Infrared Receiver.  Make sure it is firmly seated on its slot.  The receiver is connected to the System Unit by its connector and two plastic standoffs, so you won't be able to remove it without removing the System Unit itself.  The System Unit can be removed from the case by unscrewing four screws at the rear of the system, at least one screw holding down the cartridge ports and removing whatever sidecars are attached.

Rear Expansion Ports :

Except for the RCA ports for video and audio and the modem port (if one is installed), there is nothing standard about the PCjr.'s expansion ports.  However, the hardware that the PCjr. is designed to connect to is standard with one exception.  Looking at the rear of the machine, the ports are lettered as follows :

J   J   L   K   LP    T             V      M   D         S        C      P    A

J = Joystick - There are two joystick ports in the PCjr., with the first port,  sometimes called the right joystick being closest to the edge of the System Unit.  The inner port is sometimes called the left joystick.  These connect to the PCjr. Joystick, which functions just like a standard PC joystick.  The PCjr. joystick just uses a different connector.  River Raid, Demon Attack and Microsurgeon will not work without a joystick connected.  8-pins, with Pin 1 missing as the key pin.

L = Spare - These pins are not connected to anything on the system board. 6-pins, with pin 4 missing as the key pin.

K = Keyboard - For the optional Keyboard Connector.  The keyboard connector has a phone jack on one end and a large RFI ferrite choke.  It plugs into the PCjr. keyboard and allows you to use the keyboard without IR and batteries.  Third party keyboard replacements also plug into this port, but must be specifically designed for the PCjr.  If there is anything plugged into this port, then the system unit will not receive the input from the IR receiver, even if its just an unconnected wire.  6-pins, with pin 1 missing as the key pin.

LP =  Light Pen - IBM never marketed a light pen with a PCjr. style connector, but PC Enterprises did.  6-pins with pin 6 missing as the key pin.

T = Television - For the TV Connector, an RF switchbox to connect to an antenna screw terminal on a TV.  You may need a 300 to 75 Ohm balun connector.  External Audio can be heard from this connector. 6-pins, with pin 2 missing as the key pin.

M = Modem - A standard RJ-11 phone jack connector will be found here if you have an internal modem installed, otherwise it is just a hole.

V = Video - RCA Composite Video jack, better than RF, but not as sharp as :

D = Direct Drive Video - This connector supplies a CGA-compatible video signal and a mono audio signal.  The standard IBM PC Color Display Model 5153 or IBM Enhanced Color Display Model 5154 or compatible monitors can connect to it via a 9-pin adapter.  IBM released one because its PCjr. Color Display was not available at launch.  The IBM PCjr. Color Display Model 4863 has a connector that plugs directly into this port.  The IBM PCjr. Color Display has a built-in speaker with a volume control wheel for the external audio output.  The IBM PC Convertible Color Display Model 5145 also uses the same connector as the PCjr. Color display, but may or may not have a speaker for the external audio.  18-pins.  An adapter exists to allow the PCjr. and Convertible displays to work with a 9-pin D-shell port.

S = Serial - Any serial device can use this port with a proper adapter, such as from IBM.  The only device I know of that has the connector for this port is the IBM PC Compact Printer.  An adapter exists to allow the Compact Printer to be used with a standard serial port.  16-pins.

C = Cassette - IBM made a cable to interface with cassette drives and cassettes for data storage and retrieval.  It has two mini-jacks and one micro-jack.  The cassette interface is functionally identical to the interface in the IBM PC Model 5150.  8-pins, with pin 5 missing as the key pin.

P = Power Connector - See above

A = Audio - RCA Mono Audio Jack, necessary to hear sounds from the external audio unless you are using the TV Connector or the 4863 PCjr. Color Display.

Cartridge Ports :

On the front of the machine, there are two cartridge slots.  These slots are functionally identical.  Like any cartridge slot, they can accumulate dust and should be cleaned with a Q-tip and 99% Isophropyl Alcohol.  The most common cartridge that can be found is the BASIC cartridge (IBM Cartridge BASIC).  This cartridge is intended to supplement the Cassette BASIC already in the system ROM and add support for the advanced sound and video capabilities of the PCjr. and diskette drive support.  Game cartridges are generally rare, especially the good ones from Activision and Imagic.  Lotus 1-2-3 is a rare example of a cartridge program with a cartridge for both slots.

Sidecar Port :

On the side of the PCjr., there is the expansion port of the system, the sidecar port.  If there are no sidecars installed, there may be a plastic faceplate, which snaps into two holes and can be easily pried off with a screw driver or fingers.  Sidecars are pushed onto the pins, then screwed into system unit or the next sidecar with a flat head screwdriver.  You can extend the length of your system quite considerably with expansion sidecars.

Most PCjr.s have at least an IBM Parallel Printer sidecar attached, as the PCjr. did not provide a parallel port in the system unit.  The Printer sidecar provides one unidirectional parallel port using the standard DB-25 connector.

Many PCjr.s also have a Memory Expansion Attachment sidecar, from IBM or a third party company.  These sidecars add at least 128KB of RAM to the system.  Few self-booting programs will recognize more than 128KB of RAM in a PCjr.  The memory expansion's device driver must be loaded in DOS for DOS to report more than 128KB available to programs.    A device driver called JRCONFIG will work with any memory expansion.

If you have a 33W power board in the system unit and use more than two sidecars, you will need the IBM PCjr. Power Attachment sidecar, which provides more power for sidecars.  This sidecar must be inserted before any sidecars it needs to power (closer to the system unit) and has a separate power supply identical to the PCjr. system unit power supply.  They use the same connector.  With a 45W power board, you can use three sidecars comfortably.

Turning the System On :

When you turn on the screen, you will immediately see, if the system is working at all, the IBM logo and the fifteen RGBI colors that a CGA monitor can display in addition to black.  The memory will be counted and tested.  Once the memory has been counted, the screen will change to a blinking cursor, the diskette drive will seek and try to boot a disk in the drive.  Any expansions with a bootable ROM, like a hard drive or SCSI expansion interface, will attempt to boot at this time.  If neither the diskette drive nor any bootable interface is available or functioning properly, then the PCjr. will boot a cartridge, and if no cartridge is inserted, then Cassette BASIC.

Fan and Heat :

The fan inside the system blows cool air on the floppy drive and diskette.  IBM felt this was necessary to prevent a disk from melting inside the drive after heavy usage.  The fan is not intended to cool the system, that is what all the vents are for.  You can disconnect the fan without immediate apparent issue if you do not often use the disk drive, but the fan improves airflow inside the case.  This should help the Power Module (the hottest element in the system by far) and the chips underneath the floppy drive (including the CPU).  Although you may be tempted by the prospect of silent operation, leave the fan on.

Keyboard Adventure and System Diagnostics :

The PCjr. has a built-in program called Keyboard Adventure.  This can be loaded by pressing the Esc key just after Cartridge or Cassette BASIC has loaded.  You cannot have pressed any other key before pressing the Esc key.  This program was made to help introduce first-time computer users to the keyboard, and can be used to test the keyboard.  A full description of the program can be found in the PCjr. Guide to Operations manual, which came with every system.  Press Ctrl + Alt + Del to exit and reboot the system.

To start system diagnostics, any time after the PC has booted, whether to BASIC or to a disk, press Ctrl + Alt + Ins.  This will appear to reboot the system, but the memory will be counted and you will be shown a screen with several ASCII graphics and numbers underneath them.   The tests are rather cryptic and are fully explained in the Guide to Operations with the exception of  Test Tags H, I, L, M, N, O & P.  Here are a list of the Test Tags and what they test :

Test Tag 1 - Diskette Drive (requires spare floppy disk)

Test Tag 4 - 40-Column Display modes and 16KB graphics modes

Test Tag 8 - 80-Column Display modes and 32KB graphics modes (requires IBM PCjr. 64KB Memory and Display Expansion Option)

Test Tag 5 - Light Pen

Test Tag 6 - Joysticks

Test Tag 9 - internal PC Speaker and 3-voice sound (external speaker, TV Connector or PCjr. Color Monitor required)

Test Tag J & K - Cordless Keyboard  (Test Tag J treats the keyboard as a 62-key keyboard, Test Tag K treats the keyboard as if it were an IBM PC 83-key keyboard and allows you to use key combinations for the missing keys)

Test Tag G - IBM PCjr. Internal Modem

Test Tag H - IBM PC Compact Printer

Test Tag I - RS-232 (with loopback Plug)

Test Tag L & M - IBM PCjr. Cluster Adapter Attachment

Test Tag N, O & P - IBM PCjr. Speech Adapter Attachment

To escape from any test, press Fn + Break.  Press Ctrl + Alt + Del to exit and reboot the system.

Error Messages :

If you are unfortunate, you may encounter an error message.  Error messages are assigned a letter, here are a list of error messages and possible solutions :

Error A - Memory Problem, remove memory expansion sidecars and internal memory option to try to isolate which one is causing the program.  Will cause the system to hang.

Error B - Keyboard Problem, move the keyboard away from any extremely bright light source, replace the batteries, move the keyboard closer to the system if using IR and do not press any keys during the bootup process.  May cause system to hang.

Error C - Cassette Problem, press Enter to continue booting without using the cassette.  Usually caused when the cassette motor relay goes bad.

Error D - Serial Port Problem, may hang system.  Unplug any device from the serial port.

Error E - Modem Problem, press enter to continue booting without using the Modem.  Make sure the modem is properly inserted.

Error G - Cartridge Problem, may hang system if cartridge is inserted, remove cartridge.

Error H - Diskette Problem, press enter to continue booting without using the Diskette Drive.  Make sure the diskette drive adapter card is properly plugged into the system, the diskette drive is properly connected via the cable to the diskette drive adapter, the diskette drive is plugged into the power connector.

Error X - Unknown, may hang system.  May not actually exist.

Video and Audio Connections :

The PCjr. is very video friendly in that it has a composite video output jack that can connect to almost any modern TV.  You do not need a hard to find CGA compatible monitor to get video output.  The colors may not be as pure, the pixels may not be as distinct, but graphics should be visible.  If you boot to DOS and you see 80-column color fringed text, use the DOS command MODE BW80 to switch the text to black and white.  If you want more legible text, then use MODE BW40 to use a 40-column text mode.

If you find that your PCjr.'s display is off center or partially cut off, press Alt Left Arrow  to shift the visible display to the left and Alt Right Arrow to shift the visible display to the right.  You can also enable or disable the keyboard audio click by pressing Ctrl + Alt + Caps Lock

The internal beeper inside the PCjr system unit will only generate PC Speaker sounds.  If you want to hear sounds from the 3-voice chip, the PCjr. Speech Adapter or from the Cassette Port, you will need to connect the PCjr. to an amplified speaker via the RCA audio output jack, to a TV using the TV Connector switchbox, or to a 4863 PCjr. Color Display.

COM and LPT assignment.

The built in serial port is assigned to COM1 and LPT1 in the BIOS if there is no Internal Modem or Parallel Printer Attachment installed.  However, the resources used by the serial port are I/O 278H and IRQ3, which are generally assigned to COM2.  The Internal Modem uses I/O 3F8 and IRQ4, the BIOS assigns the Modem to COM1 if it is installed and the serial port becomes COM2.  If the Parallel Printer Attachment is installed, it becomes LPT1 and you may need to redirect LPT1 to COM1 or COM2 to print to the serial-based Compact Printer.

Recommended Programs :

Most DOS programs will require a 256KB PCjr., so if you don't have one you are probably going to be limited to self-booting (PC Booter) programs.  King's Quest I & II, The Black Cauldron and Below the Root are excellent adventure games that take advantage of the enhanced graphics and sound features of the PCjr.  Super Boulderdash and Jumpman are solid ports of these classic games with PCjr. features.  Microsoft Flight Simulator 2.0 looks best on the PCjr. and can take advantage of a 256KB PCjr.

The Device Driver JRCONFIG is a must if you are running a 256KB or more PCjr. in DOS.  The PCjr. was released with PC-DOS 2.1, and was officially last supported in PC-DOS 4.0.  DOS 5.0 and above require patching via DEBUG to run on the PCjr.  While DOS 3.3 and below can run in a 128KB PCjr., DOS 4.0 and above are not likely to leave much memory left for programs unless 256KB or more is in the system.

PCjr. Post-Cancellation, or the Afterlife of a Flop

November 1, 1983 - IBM announced the PCjr. to great fanfare.  Commentators predicted and expected that IBM's new system would bring order and compatibility to the fractured home computer market just as it had the business market with the PC and XT.  Magazines are published geared to the new system and software is updated to support the new features and otherwise run on the PCjr.

March 18, 1985 - IBM announced that it was discontinuing manufacturing the PCjr. system in April, intending to sell the remaining stock at a discount and not release any further peripherals or upgrades for the system.  It would continue to service the machines within their warranty period.

The reasons for the PCjr.'s failure have been well-documented elsewhere.  Had it not been discontinued, it would have probably have been sold until April 1, 1987, when the rest of the PC family was retired to make way for the PS/2 machines.  However, the public apathy for the machine a result of the machine's high price, competition from other home computers, miserable chicklet keyboard, incompatibilities with PC software and the high cost of the upgrades meant that despite IBM's weight in the industry, it had to be withdrawn.

What happens when a buyer, believing in the solid name of IBM, buys a computer whose lifespan had just been reduced from years to months or even days?  Most PCjr.s had been sold during the 1984 Christmas season.  IBM not only abandoned the PCjr, but also abandoned its family and entertainment software products.  With one exception, the last games IBM marketed for the PC or PCjr. were released in 1985.  While it tried to put on a brave face by announcing a new and improved successor to the Jr., nothing came of it in the United States.  The closest thing to a PCjr. replacement was the PC JX, essentially the next generation of PCjr. released only in Japan, Australia and New Zealand.  It sold very poorly.  IBM would not return to the market with a home-friendly machine until the PS/1 in 1990.

When IBM announced the PCjr was being discontinued, software developers were the first to jump ship.  Bill Gates' Microsoft, which had heavily supported the Jr. with the Microsoft Booster sidecar and an updated Flight Simulator 2.0 which took advantage of the Jr.'s capabilities, eliminated its PCjr. development almost overnight.  Spinnaker Software tried to burn its PCjr.s in a great bonfire, only to find out that they wouldn't burn!.  Sierra On-line quickly focused its efforts to the PC and the Tandy platform, and many other game companies did the same.  Any software companies who had not yet jumped on the PCjr. bandwagon certainly were not about to start supporting the machine once its discontinuance had been announced.

All PCjr. magazines had already folded by December, 1984, in response to the weak market for the PCjr. before the 1984 Christmas season.  Peter Norton had written a trilogy of how-to books for the PCjr., Discovering the PCjr, Exploring the PCjr and Mastering the PCjr, but the third book was never released due to the discontinuing of the PCjr.

Every game that had support for the PCjr.'s graphics and sound, as identified in an earlier post on this blog, were all self-booting games released in 1984 or 1985.  In 1986, games were more and more beginning to run in DOS and very few advertised PCjr. support.  Any DOS games from 1986 or later that did run on the PCjr., with expanded memory, tended to treat it just like an IBM PC with CGA.  Sierra Online was the main exception, because its AGI engine had been originally built on the PCjr. and thus it was no great effort to make sure its games continued to run on it.  All Sierra AGI DOS games thus will work on the PCjr.  Some of the AGI booters as marketed by Tandy may not.  So will Thexder, 3-D Helicopter Simulator, later versions of Silpheed but later Game Arts/Falcom ports will not.  Early versions of King's Quest IV, Leisure Suit Larry II and perhaps Police Quest II specifically did not run on the PCjr., but later versions of these SCI engine games and other 16-color SCI0 engine games would run on a PCjr.

For the home user that had almost certainly dropped over $1,000 on the PCjr., it was not so easy to discard the computer like a bad memory as the mainstream industry had done.  Some undoubtedly felt that their purchase was now useless and consigned it to the attic or the basement.  Others probably only used it until they could afford something better.  But for some of the owners of the approximately 500,000 PCjr.s IBM shipped out of its factories, they were not going to just let the machine gather dust and mildew.

Those who decided to stick with it and make a go with the Jr. were not completely left out in the cold, hardware wise.  The hardware expansion market for the PCjr. had dwindled considerably, but there were companies still trying to fulfill the need for upgrades.  Comapnies like Racore and Legacy and eventually PC Enterprises stepped up to offer an assortment of sidecars, cartridges, peripherals and expansion chassis to expand the capabilities of the comparatively crippled PCjr.  You could obtain a second floppy drive, a hard drive, 640KB of RAM, a clock/calendar chip, replacement keyboards, CPU accelerator boards, a coprocessor upgrade, Hayes compatible modems, and eventually SCSI adapters, VGA and Sound Blaster clones.  They sold compatibility cartridges that would fool software programs into thinking they were running on a PC.  In short, you could upgrade your jr. almost as much as you could a PC or XT, but you had to do your research and purchase via mail order.  However, these expansions were sold to a limited market and pricey, often pricier than comparative PC expansions.  Also, with the monitor,  sidecars, expansion chassis and many adapters and cables to connect to standard PC peripherals, the PCjr. would eventually begin to look like a big "L" shaped spider.  PC Enterprises was in business the longest, finally closing its doors around the turn of the century.

For software, after 1985 things became really iffy for PCjr. owners.  Most PC game software (except Sierra), either only supported PC CGA, Hercules or EGA graphics and PC Speaker sound, and most of it required 256KB or more.  That software was indifferent to the PCjr. but if DOS-based, often would run if the PCjr had sufficient memory.  All IBM PCs and most clones by 1985 came with 256KB.  While the Tandy 1000 also only came with 128KB, it was designed for 640KB, the PCjr. was designed for 128KB. While Tandy's memory expansions were pricey at first, they also added DMA, a widely appreciated feature which was difficult to implement on the PCjr.

For software now supporting Tandy graphics and sound, often the extra effort at trying to support a "dead" computer meant that developers did not bother, even though IBM made half a million PCjr.s and sold 400,000 of them.  Many developers did not have a PCjr. to test with.  Even though the IBM PCjr. and the Tandy 1000 operate almost identically, there are enough differences that making sure that software ran reliably on both was a real headache.  Besides, with DMA, a relocatable video buffer, no extra latency between video and RAM access in the first 128KB, PC compatible floppy I/O addresses, two floppy drive support, easier hard disk support, better keyboard, more standard peripheral ports and faster Tandys, what time-pressed programmer wanted even to test their code on a PCjr.?

Here are some of the issues facing the programmer who wanted to make his software, designed on a Tandy 1000, work on a PCjr. :

Memory Issues - In the IBM PCjr., the first 128KB of memory is governed by the video controller.  This was done to simplify the design, eliminate the need for a DMA controller or separate circuitry to refresh the DRAM.  The video controller would read all the RAM sixty times a second.  However, this came at the expense of performance, as the video circuitry and the CPU had to contend with each other's access to RAM.  Any RAM added via sidecar above 128KB had its own refresh controller and thus accesses to and from this RAM was as fast as a PC.  So in the PCjr. there was a combination of "slow" RAM and "fast" RAM.  Tandy implemented this same feature in its machine, but unlike the PCjr, Tandy made sure that there was no adverse impact on performance.  So there is no "slow" and "fast" distinction in a Tandy, and any programmer desiring a consistent speed for their operations would have this headache.

The addition of memory above 128KB on a PCjr. does not give you as much memory as you would think. Adding more memory requires a DOS memory driver to configure the system to use the memory. Otherwise programs will not recognize or use it (with the rare exception of the Flight Simulator II booter.)  The memory driver will set the free RAM from 128KB upward and leave the slow first 128KB to the Video, BIOS, DOS and may configure the rest as a RAM disk.  A Tandy does not require this and can have more free RAM available to programs because its DOS does not need memory drivers or treat the first 128KB as non-user memory.  Generally speaking, a Tandy without the 768 RAM upgrade will report a maximum of 624KB available to DOS programs while a PCjr. will report 608KB.

Video Issues - Both the Tandy 1000 and IBM PCjr. have a video memory window at B8000 to maintain CGA compatibility.  Until the (upgraded) Tandy 1000 TX, there would be no actual memory in this area, it would redirect to the designated address of the main memory where the video buffer was located. However, IBM only provided a 16KB window at B8000-BBFFF while Tandy allowed access to a 32KB window at B8000-BFFFF.  For the 160x200x16 mode or any of the CGA modes, this made no difference because one screen's worth of these graphics modes use 16KB.  The 320x200x16 and 640x200x4 modes require a 32KB buffer.  On any Tandy 1000, the programmer could use the B8000 window and not have to bother about figuring out where the video buffer really began.  If the programmer made no changes to his code for the PCjr., only every other line would be visible.  This gave rise to the "Tandy-mod" for the PCjr., where a chip would be soldered into the PCjr. to show all the lines.  To support the PCjr., the programmer would have to write directly to the portion of memory which the video circuitry was using when using a 32KB mode.

The IBM PCjr. had a chip called the Video Gate Array (VGA) that controlled the graphics modes in conjunction with the MC6845.  Tandy implemented this VGA, but its implementation was a little different.  The PCjr.'s VGA had an address and data write register at port 3DA, with the write mode switched by a read to port 3DA.  Tandy must have decided this was inefficient, so address writes in its VGA went to port 3DA and data writes to port 3DD.  Any program that writes to the VGA must be aware of this difference.

Moreover, the actual registers that controlled the modes were implemented differently in the Tandy and PCjr.  In the Tandy, to restore compatibility with the PC CGA, Tandy's VGA supports I/O ports 3D8 (Mode Control) and 3D9 (Color Select).  The PCjr. does not implement these ports, and handles all of the Mode Control functions in the VGA internal ports, most important is port 00.  Tandy's VGA does not implement port 00 in its VGA, instead relying mainly on 3D9.  The differences in the VGA ports (and there are others) is another headache for the programmer who wants to directly program the graphics registers.

Floppy Drive Issues - Tandy followed the IBM PC and used addresses 3F0-3F7 to communicate with the Floppy Disk Controller.  The IBM PCjr. uses addresses F0-F7.  While software using DOS or BIOS routines should not care, since using DOS or BIOS takes care of disk transfers, programs accessing the disk controller directly would need to be modified for the PCjr.  Booter programs and copy protection routines, important in the 1980s, frequently accessed the hardware directly to obfuscate the code or to improve performance.  Moreover, the PCjr. had no provision for DMA while every Tandy 1000 had it or could be upgraded to it.  DMA made for faster disk transfers, and timing critical disk functions would be affected by this.

Keyboard Issues - Tandy uses a 90-key keyboard, and its raw scan codes are identical or similar to the 83-key IBM PC keyboard, except for those keys unique to the Tandy keyboard.  The 62-key PCjr. keyboard with its different arrangement uses different scancodes for the keys that exist on the 83-key PC keyboard.  This is typically with the Fn key, and the scancode pair is then translated by the BIOS for the PC scancode. Tandy's keyboard uses IRQ1, like the PC's, while the PCjr's keyboard uses NMI.  All these make for issues with low level keyboard reading routines.

Even with these issues, there was considerable life left in the old Peanut.  It was quite possible to purchase a PCjr. in 1987, often at a heavily discounted price.  IBM provided some support for the Jr. until that time at least.

In the 1980s, there were often users groups created in a geographical area dedicated to a particular home computer.  Perhaps spurred in part by the abandonment of the platform, PCjr. users groups were formed in several parts of the country and operated for many years, some well into the 1990s.  The most famous ones were the Eugene, Oregon PCjr. Users Group and the Metro PCjr. Users Group in the metro-Washington D.C. area.  These groups provided advice, support and meetings where PCjr. owners could trade the latest news and gossip, review hardware and software and try to solve problems.  The groups also had their own Bulletin Board Services (BBSs), where people could post on message boards and download patches and programs.  Newsletters in print and on disk were also a feature of these clubs.

Many issues of one particular newsletter, the jr Newsletter, are available online.  The jr Newsletter ran from June 1986 to at least October 1993.  This newsletter provided tips, fixes and advertising for PCjr. specific peripherals.  IBM's BBS also had PCjr. specific files for a long time.  Some games, sometimes unintentionally, still supported PCjr. graphics and sound or were hacked to do so.  Electronic Arts, for example, included a PCjr. patch for Starflight made by a PCjr. owner who submitted it to the company.

The PCjr.'s life was not totally brought to an abrupt end in March 1985, despite the views of many at the time and since.  Extending the lifespan of the machine required the user to become intimately familiar with this machine's hardware and the software available for it.  It is an important example of how ordinary people, despite mainstream indifference (and often contempt) and market forces which should have condemned the machine into a nearly-forgotten footnote of computing history, allowed a unique computer to achieve some measure of the hoped-for potential intended for the machine in 1983.

M.U.L.E. - The PC Port on Real Hardware

1985 was the last year that IBM was known to have published any games for its IBM PC family.  It had seen games as one of the things that consumers could do with their PCs, and had released Microsoft Adventure at the launch of the original IBM PC Model 5150.  However, by 1985 IBM no longer looked to the home consumer market as a primary market, and thus the number of games it published dwindled to nothing.  One of the last titles it published was a port of Electronic Arts and Ozark Softscape's classic M.U.L.E.  This port was ported by K-Byte Software and released very quietly.  In fact, until 2012, no one had probably played it for 15 years.  It remained a mystery and completely unavailable until someone opened up a box of old IBM games, found it, became aware of its significance and allowed it to be cracked and distributed.  The story is recited here : http://www.worldofmule.net/tiki-index.php?page=IBM+PC  Others have analyzed it for differences between it and the Atari 400/800 original and Commodore 64 port, read here : http://bringerp.free.fr/forum/viewtopic.php?f=1&t=166  In this port I will discuss how it actually plays on the systems it was intended for.

Speed

M.U.L.E. for the IBM PC requires 128KB of RAM and a CGA card.  It only supports PC speaker sound and music and one physical joystick.  The cover explicitly lists the IBM PC (Model 5150) IBM PC/XT, IBM PC Portable and IBM PCjr. as supported systems.  Note that it does not mention the IBM PC AT, which was released in 1984 and used a 6MHz 80286 CPU.  This game is speed sensitive and the game will probably run to fast on the AT, which is roughly three times as fast as the PC or XT.  Running on more modestly upgraded or faster systems, like a V20 IBM PC, XT or PCjr. or a Tandy 1000EX, SX or HX at 7.16MHz will not give such a noticeable effect on speed to make the game unplayable.

On the packaging, there is no explicit mention of the IBM Personal Computer AT.  This is probably not an oversight, as some other IBM released games from 1984-85 explicitly included the AT in the list of supported systems on the box.  The AT was released in 1984 and thus its omission was almost certainly intentional.  (K-Byte does not seem like an outfit that could afford an AT).  The game adjusts its speed for a PCjr., so if you have an exotic speedup method in your PCjr. (V20 is fine), the game will probably run too fast.

Graphics

IBM PC with CGA on an RGB Monitor

On an IBM PC, XT or 100% compatible system with a CGA card, the game will use the 320x200 Mode 4, Palette 0 (cyan, magenta, white) in low intensity with a bright white background/border.  While the game is playable on an RGB monitor, it was clearly meant to be connected to a TV or color composite monitor.  Instead of stripey cyan and magenta graphics for the four players and their plots, composite color gives brown-gold, orange, red and light blue.  It seems clear that a late CGA card was intended because the text (white/light gray against bright white) on a real color composite monitor or TV is almost totally illegible with an early CGA card (without adjustments to the brightness and contrast).  EGA and VGA cards probably will not display the intended colors.

IBM PC with Old CGA on a Composite Monitor 

It was a long-standing myth that this game was either released solely for the PCjr. or took advantage of the PCjr.'s advanced graphics and sound capabilities compared to the IBM PC with CGA and PC Speaker.  The sound is exactly the same on either the IBM PC or PCjr.

IBM PC with New CGA on a Composite Monitor

On an IBM PCjr., the game uses a 320x200 resolution four color mode with colors similar to CGA.  The bright white background is the same, but the RGB colors are now light cyan, light magenta and white.  The pixel patterns are not the same as with a non-PCjr., but still show that the game was meant to be displayed on a color composite monitor or TV.  The PCjr. artifact colors the programmers chose are not as distinct as on a CGA card, there are two shades of magenta or purple and two shades of cyan or blue-green to choose from.


IBM PCjr. with an RGB Monitor

Control

This section requires a digression.  When M.U.L.E. was released for the Atari home computer systems in 1983, officially it could only run on the Atari 800 with 48KB of RAM.  The Atari 400 was not easily upgradeable to 48KB (but when upgraded was indistinguishable from an 800 to software) and the 1200XL, 600XL, 800XL and later machines only had two joystick ports.  For the Atari original, there was no keyboard control of the characters.  At least one joystick was required, and a pair of paddles could be used by two players in the auctions.  If there were fewer joysticks than human players, the players had to share the joystick for each player's main turn.

IBM PCjr. on a Composite Monitor

The Commodore 64 only had two joystick ports, and its port of MULE did not support paddles.  Thus, players three and four had to use a pair of keyboard keys during the auctions, and the joysticks had to be shared during the player's main turns.

The IBM port only supported one joystick, notwithstanding the IBM Game Control Adapter could support two joysticks with a Y-splitter and the IBM PCjr. had two distinct joystick ports.  Unlike the Atari and Commodore versions, it did not require a joystick to play the game.  If you did not have a joystick, the arrow keys could be used to control the player during his or her main turn.  Only the main four cardinal directions could be used, the "diagonals", 1, 3, 7 and 9, do nothing on the PC keyboard.  The PCjr.'s keyboard has no numberpad, only dedicated cursor keys.

For the auction phase, the keyboard controls for each player on the IBM PC are as follows :

Player -  1  2  3  4

Up     - F1  W  O  ↑

Down   - F5  X  .  ↓

On the PCjr., the keyboard controls are different, due to the differing layout of the PCjr.'s keyboard :

Player -  1  2  3  4

Up     -  W  Y  [  ↑

Down   -  Z  B  /  ↓

There is a game crashing bug when selecting joystick control with four planeteers.  The Alt key is pressed to determine which player will use the joystick.  However, if players 1-3 use the joystick, the game will not allow you to press key to select player 4.  Player 4 must use the joystick in this case.

This game was designed for the IBM PC 83-key keyboard.  On the 83-key keyboard, Player 1's auction up key, F1 is above the down key, F5, by one key, just like the keys for Players 2-4.  On a 101-key keyboard, F1 is three keys to the left of F5.  This arrangement simply does not work well with three other people.

The keyboard handling takes some getting used to.  The Enter key corresponds to the joystick button.  When doing anything requiring a button press like selecting a land plot, beginning your turn or installing a M.U.L.E., it is best to hold the button down until the game acknowledges the input.

The Alt key functions essentially as a speedup key in the game.  It can end auctions after everybody has bought and sold what they can.  It can bypass the summary screen and the chance animations.

The Esc key acts as a pause key.  Unfortunately, it will cause the game to freeze on a Tandy 1000 90-key keyboard.  If you are going to play M.U.L.E. on a Tandy 1000, I would advise using the joystick and setting the speed machine to slow (if an EX, HX, SX or faster) at boot time.  On the Tandy 1000 90-key keyboard, the Esc key is right below the F1 key, making it too easy to press if you are controlling Player 1.  The composite colors on a Tandy with an RCA video jack (TX or earlier) will look different than on an IBM PC with a CGA card.

Finally, the game can be saved in progress by pressing Ctrl-Q.  This does not appear to be a feature of the earlier versions.