Tuesday, March 24, 2015

IBM JX - PCjr. 2.0



In 1985, IBM released a computer in Japan, Australia and New Zealand called the IBM JX, Model 5511.  Essentially it was an ugraded PCjr., and perhaps what the PCjr. should have been.  In fact, upon rumors of the JX making it to the United States, at least one commentator dubbed it the PCjr. 2.  Released in 1985, just as the PCjr. was being discontinued, it proved to be the last machine by IBM with any substantial PCjr. compatibility.  However, it was not successful anywhere it was released and consequently is extremely obscure today.

The IBM JX shares much of the design philosphy of the PCjr.  It had a wireless keyboard with an optional cable.  It had two cartridge ports, the PCjr. sound chip and a graphics chip capable of doing all the PCjr. modes and (maybe) more. It had unique slots inside the machine for making upgrading easy.  It has support for some peripherals built in.  By 1984 third parties had already been selling stackable PCjr. expansions where you could fit a second floppy drive or a hard drive.  IBM sold two for the JX, one added a 5.25" drive, the other a 10MB hard drive.

The machine also had several good ideas.  First, there was a standard parallel port built in.  The parallel port sidecar was a very popular PCjr. upgrade, but the PCjr. only had a serial port built in.  This was still before the days of the ubiquitous serial mouse, so this was a very smart idea from IBM.  The JX's power supply was completely internal in a cage whereas the PCjr. had a split power supply and a huge black brick on the floor.  There were two types of keyboard available, both had function keys and the larger keyboard had a numeric keypad.  The keyswitches use Alps switches, even the small function keys.  The PCjr. keyboards use rubber domes.  You can see the two types of keyboards on this page : http://computers.popcorn.cx/ibm/jx/

The English compact JX keyboard 79 keys compared to the 62 keys of the PCjr.'s keyboard.   It has a separate Scroll Lock/Break and Print Screen/*, but still has the function key activated Pause and Echo under the Q and E keys.  It also has a separate Home key and a second Space and Tab keys.  It also has a separate ~/` key.  The full keyboard adds 19 more keys for a total of 98 keys, including a second set of Alt and Fn keys, the numeric keypad keys, an extra Enter key and numeric symbols.  The Japanese JX keyboards have four additional keys, they split the spacebar into three keys.

The machine was intended to be upgraded beyond 128KB of RAM.  It appears to have separate RAM for the video and Cartridge BASIC built-in, see below for more details.  Finally, there was an outlet on the back to plug the monitor power cable.  Cosmetically, the machine came in black for Australia and New Zealand and black or white for Japan and also was made of sheet metal instead of the plastic PCjr.  It allowed the user to use three floppy drives, and the floppy controller was underneath the 3.5" drives instead of taking up an additional slot.  I also believe that the video RAM was separate from the main memory, so there would have been no performance issues with a 128KB JX like there is on a 128KB PCjr.

Unfortunately, the designers were held back by some of the inherent design limitations of the PCjr.   First, the most basic system only comes with 64KB, and another 64KB is added via a special memory slot (silkscreened EXRAM64), just like with the PCjr.  The JX has a second memory (silkscreened EXRAM128) slot to add more memory, and IBM supplied a 128KB, a 256KB or a 384KB card.  From IBM the system would be limited to 512KB of RAM, but third parties offered larger memory expansion cards to bring the system up to 768KB (probably only 704-736KB usable).  Second are the proprietary ports in the back.  The monitor uses a DA-15 port instead of the usual DE-9 port.  The keyboard, light pen, cassette and two joystick ports use mini-DINs.  The keyboard uses a Mini-DIN-6 just like the IBM PS/2 keyboard port, but the machine will not work with a PS/2 keyboard.  Each joystick uses a Mini-DIN-7 port.  The cassette cable uses a Mini-DIN-8 port.  The lightpen looks like it uses a non-standard Mini-DIN-7 port.  While the PC was not nearly as popular in these countries, this made it more difficult to not buy from IBM.  Third, adding a serial port required a special card that plugged into a silkscreened RS232C slot the main chassis, whereas it was built-in on the PCjr. instead of a parallel port.  Fourth, there appears to be no DMA capacity in the system, unless perhaps added by the hard drive upgrade.

Here you can see a picture of the front with a 5.25" diskette drive adapter on top of the main system unit and a rear shot showing all the mini-DIN style ports : http://www.pbase.com/sinisterdragon/ibm_5511

I have seen a flyer detailing five Japanese models of the JX, named JX1-JX5 : http://msibata.org/ibmpc/image/jx15.jpg  J1 has 64KB of RAM and 32KB of VRAM, JX2 has 128KB of RAM and 32KB of VRAM, JX3 128KB of RAM and 64KB of VRAM, JX4 256KB of RAM, 64KB of VRAM, and JX5 384KB RAM/64KB VRAM.  JX5 (which came later and has the model designation 5510) also has a switchable 8088 CPU speed of 4.77MHz and 7.2MHz (probably 7.159MHz, exactly 1.5x the 4.77MHz speed.)  From this pattern, I would postulate that the JX has separate main and video memory, unlike the PCjr.'s which is shared in the first 128KB.  There are eight 64Kx1 DRAM chips and four 16Kx4 DRAM chips on the system board, which further supports my theory.  32KB allows up to a 640x200x4 resolution, and 64KB would allow a 720x512 monochrome mode, which is what the JX3 advertises. I would suspect that the 32KB of RAM sat at the CGA address range of B800-BFFF and the extra 32KB provided on the EXVIDEO card sits at B000-B7FF and acts similar to a Monochrome and Hercules graphics cards.  More specifications can be found here : http://ja.wikipedia.org/wiki/IBM_JX

The JX1 came with no disk drives, but the JX2-JX5 came with two 3.5" drives.  A special monitor is required for the 720x512 mode.  Kanji character support required a separate daughter board that plugged into two sockets on the board, one silkscreened KANJIROM, the other silkscreened SYSTEM ROM.  I believe the Kanji dot patterns took a full 128KB of ROM chips.  A 15x16 Kanji symbol requires 30-32 bytes to display in a single color format.  128KB would be able to store the patterns for at least 4,096 kanji characters.  This would be sufficient for everyday Japanese usage, because 2,000-3,000 characters are in common usage in Japan.

The Australian and New Zealand models were not so advanced as the Japanese models.  They had no need for kanji support or the high resolution graphics support.  Three models were advertised, no floppy, one floppy or two floppies.  There is no mention in the price list for a video upgrade adapter.  One person who had an Oceanian JX indicated that it only had three physical upgrade slots.  There were only silkscreened through holes for the KANJIROM and EXVIDEO slot.  Of course, it has a 200-240VAC/50/60Hz power supply whereas the Japanese model would be rated for 100VAC/50/60Hz.  The Japanese keyboard has more keys and hiragana on the keys.  This is what it looks like : http://deskthority.net/wiki/File:IBM_JX-JW_6343690_--_front.jpg  

In some ways, however, the JX was worse than the machine it intended to replace.  First, it came with 3.5" drives.  In 1985, 5.25" disks were what everyone was using.  Nobody outside IBM would be able to provide PC compatible software on that format at first. JX users were punished with being early adopters or buying the expensive 5.25" upgrade.  To add insult to injury, the BIOS and DOS (PC-DOS 2.11) recognized the 3.5" disks as 40 track disks.  There was no capacity increase until IBM released PC-DOS 3.21 with an upgraded BIOS chip in 1985.  Finally, I have read of several complaints from Australian and New Zealand individuals who used the machine in the past to complain about extremely poor compatibility with PC software.  Between the disks, the lack of Tandy 1000 machines and the general unpopularity of the machine, this computer would have had serious issues with software.

Second, the JX has nothing like the PCjr.'s sidecar bus in the main system, but the 5.25" floppy drive expansion adds 5 expansion slots that probably nothing used.  Upgrades beyond what the slots do support internally required another box to sit on top of the main system.  In other words, there was no such thing as a cheap upgrade outside the system.  Third, the JX may lose composite video support, which would have been useful only in Japan because composite video with CGA or PCjr. is NTSC-based.  There is no video RCA jack as there is on the PCjr., but it is possible that one of the pins on the video port may output composite video, which an IBM adapter would provide.   The video port also outputs sound, just like on the PCjr. and is intended to connect to a monitor with the identical features to the PCjr 4863 monitor.  Fourth, the JX is far less easy to repair because IBM used seven surface mounted proprietary chips in the JX compared to the one proprietary DIP chip for the video controller in the PCjr.  

When you boot the system, you will see the same screen familiar to all PCjr. owners with the large IBM logo, the 16 colors and the memory count.  You will also see the same BASIC version J1.0 as you would with a PCjr with Cartridge BASIC : http://s83.photobucket.com/user/DrRabid/library/Vintage/IBM%20PC%20JX?sort=3&page=1

However, if you had a Japanese machine with the EXVIDEO and Kanji upgrade, you would probably see this instead : http://blog.goo.ne.jp/minami1001kaze/e/5900912c2257843e031153cb1f277713  You would also need a high resolution monitor like the 5515 to display the higher resolution modes.  In this monitor color #6 is dark yellow, not brown.  In addition to a monochrome 720x512 mode, ther was a four color 360x512 mode and a sixteen color 640x200 mode.  There is an extended display mode cartridge which adds support for the modes that work with Kanji to BASIC and Japanese PC-DOS.  There is also apparently an English language cartridge as well.

Even with all this information, the lack of a Technical Reference for the machine makes it very difficult to answer all questions about it.  I can only assume, for example, that the cartridge slots of this machine are compatible with the PCjr. and there is no performance hit in the first 128KB of RAM.  I also assume that the system still needs a device driver loaded in DOS to access memory above 128KB or have a program specifically tailored for the JX.  I do not know whether the keyboard is completely compatible with programs expecting to use the PCjr.'s keyboard.  

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