In this entry I will discuss one of my favorite video cards, discuss its features and why I recommend it to anyone building a vintage computer system. The card in question, as mentioned in the title to this post, is the Diamond Stealth 24 VLB. It looks like this :
Thanks to http://www.vgamuseum.info for the photograph.
As you probably know, the edge connector on the back of the card is for the VESA Local Bus (VLB) slot. This bus is almost totally exclusive to 486 processors, as it is essentially an extension of the 486 bus. If you are building a 486 system, VLB cards are an excellent fit for video if your motherboard supports them. (Whether they are as good a fit for hard drive interfaces is a debate that must be put off for another day.) The ISA bus is just too slow for a 486 and games needing fast video like DOOM, especially as so many boards have VLB slots.
Later 486 motherboards tend to support PCI slots, but the conventional wisdom of the time was that 486 PCI implementations were generally immature. PCI slots came into their own on Pentium Socket 7 motherboards. Small wonder that the number of Pentium mainboard chipset makers and motherboard builders seemed to shrink dramatically. In my opinion a VLB slot is to a 486 as a PCI slot is to a Pentium as an AGP slot is to a Pentium II and above
Back to this board, you can see that it has eight pieces of V53C104 DRAMs. Each chip supports 256kx4 bits.. Eight chips gives you 8 megabits or 1 megabyte of video memory. This is four times the basic VGA memory requirement. The PLCC chip near the VGA connector is a Diamond SS2410 High/True-Color DAC. This is an optional feature for the S3 805 chip. Without this kind of DAC or an equivalent DAC, the card would only be able to support 8-bit color resolutions. With the DAC, it can support 15-bit, 16-bit or 24-bit color resolutions as the maximum memory allows.
The S3 805 can support up to 2 megabytes of video memory, but this was a cheap accelerator card and cannot be upgraded to 2 megabytes. 1 Megabyte of video memory was standard for VLB video cards, 2MB was a premium card, and 4MB was almost unheard of.
This card boasts some VESA compliance. The Modes 101h-104h are VESA modes. The only mode of any real importance for DOS is the 640x480x256 and 15/16-bit and 800x600x16 and 256 modes. It does support 640x400x256, even though it does not list VESA Mode 100h in its supported display modes. Rise of the Robots uses that resolution and works fine with the card at that resolution. System Shock CD does not allow that mode to be selected, so UniVBE may be necessary to play the game in that mode. It can support refresh rates up to 72Hz at 1024x768 or below and refresh rate of 60Hz at 1280x1024. These graphics modes were tested with WHATVGA.EXE and work :
101h - 640x480x256 packed
102h - 800x600x16 planar (also 6Ah)
103h - 800x600x256 packed
104h - 1024x768x16 planar
105h - 1024x768x256 packed
106h - 1280x1024x16 planar
110h - 640x480x32K
111h - 640x480x64K
112h - 640x480x16M
113h - 800x600x32K
114h - 800x600x64K
124h - 1152x864x256 packed (did not work in WHATVGA)
206h - 1280x960x16 packed (not a VESA mode)
208h - 1280x1024x16 planar (not a VESA mode)
WHATVGA.EXE had some issues with displaying planar 1024x768 and 1280x1024 modes, and did not display the extended text modes 54h 132x43 and 55h 132x25.
Not much is known about the BIOS revisions. I have read that there exist 1.11, 1.24 and 2.01, the last being required to use the latest windows drivers. My card has 2.02.
One slightly annoying issue this card has is that its I/O addresses conflict with the default COM4 addresses, 2E8-2EF. This is due to its 8514/A derived design and is not unique to this card. It has a jumper to enable or disable IRQ2, but few games required that functionality on a VGA card. I have not found any problems with it and an MPU-401, which also uses IRQ2 by default. Games rarely use the IRQ functionality of the MPU-401 anyway.
Diamond still provides drivers for the Stealth 24 VLB and other cards on its website for Windows 3.1. This will allow you to use better resolutions than Windows 3.1 default VGA 640x480x16 resolution. Get them here : http://www.dmmdownload.com/legacy.php. These cards tend to be among the most plentiful VLB cards you can find today. Windows 95 comes with drivers for the card.
Game compatibility with EGA and VGA games is excellent. I have tested the card with almost every piece of software on this chart : http://gona.mactar.hu/DOS_TESTS/. I did not try Quake, Duke Nukem 3D above 640x480 or Tomb Raider. Software works perfectly (Commander Keen 4-6 needs the SVGA Compatibility option turned on, as does Dangerous Dave and Keen Dreams with the /comp switch). Silpheed has some minor extraneous flickering lines during its intro, but they do not appear during the actual gameplay. UNIVBE works with the chipset, and there is a utility to set the refresh rates, look for S3REFRSH.ZIP. It reports that you can set 640x480, 800x600, 1024x768 and 1280x1024 to 60Hz or 70Hz/72Hz, 800x600 at 56Hz and 1024x768 and 1280x1024 to 43Hz/45Hz interlaced.
As far as speed goes, consider these videos with the card being put to work in my 486DX2/66 system :
According to this article, it should have good Windows 3.1 acceleration features and speed : http://books.google.cz/books?id=PTwEAAAAMBAJ&pg=PA39&dq=Diamond+Stealth+24&hl=cs&ei=q6ROTOe0EIWL4QafmuyUCA&sa=X&oi=book_result&ct=result&resnum=3&ved=0CDMQ6AEwAg#v=onepage&q=Diamond%20Stealth%2024&f=false