IBM SVGA Chipset

SVGA Developments
SVGA Variants
Driver Support

Information collected by Wolfgang Gehl. Edited by Major Tom.


SVGA Developments

While playing with a Solaris setup on a 9595 I ended up creating a DOS partition and giving SVGA Adapter/A a try.
This mysterious card currently has no OS support beside OS/2 with VGA resolution and 256 colors and VESA VBE support for DOS.

First I tried the VESA driver from m95svga.exe. It offers VESA VBE 1.2 support for 256 colors for resolutions up to 800x600 pixels customized for the display's horizontal refresh rate. Since I use a LCD monitor, I disabled 640x400 and the 16 colors interlaced 1024x768 mode and choose 60 Hz for 640x480 and 800x600 mode.

Do you remember trying to play "Simcity 2000" or "The Settlers" with XGA/2? Never got it running. With SVGA/A and loaded VESA driver these games are playable without a hitch. It's kind of a crazy to play DOS SVGA games on a 9595 RAID5 Server, however, it works!

Simcity 2k for DOS contains a VESA driver collection with an IBM directory. Inside are two VESA drivers. One is for XGA/XGA2 (for Simcity dysfunctional) the other one is for the PS/2 25SX planar video. A look at Williamís 25SX site shows that the SVGA/A chipset is sitting on the 25SX planar. And he mentions that it is common on 40SX and 56/57 SX/SLC planars too.

A search for "IBM 84F7985" took me to a thread on a PS/1 forum with the title The mistery of the PS/1 2121ís (S)VGA.

Obviously IBM used this chip in several x86 machines, and for us most important, inside the micro channel PS/2 ThinkPads too. A ThinkPad without Windows drivers is hard to imagine. And right, Louis has the 256 colors Windows 3.1 driver, which is in fact the 25SX_AND_700C_AND_720C display driver: 9552 700C
Since we have the driver, we have the chipset name too: IBMVGA256c

Well, don't expect to much, the Windows 3.1x setup offers 256 colors for 640x480 pixels only. It works in conjunction with the DOS VESA VBE driver and seems to be an early if not the first Windows VESA VBE driver at all. I've tested with windows 3.1, 3.11, and 95. With 95 the 16-bit driver slows down the system and there are severe incompatibilities e.g. with explorer.exe.

Below is the (incomplete) information I could find so far.


SVGA Variants

IBM PS/1 2121 (link)

Year1991 (?)
Video ChipIBM 84F7985 (= TI CF62011BPC) IBMVGA256c
RAMDACINMOS IMSG171P-35
35 MHz 8-bit DAC up to 256 colors from a total of 262,144 colors
RAM256 KB 100 ns VRAM

IBM PS/1 Pro 2123

Year1991 (?)
Video ChipIBM 84F7985 IBMVGA256c
RAMDACINMOS IMSG171P-50
50 MHz 8-bit DAC up to 256 colors from a total of 262,144 colors
RAM256 KB 80 ns VRAM

IBM PS/2 8535SX and 8540SX

Year1991
Video ChipIBM 84F7985 IBMVGA256c
RAMDACINMOS IMSG171P-50
50 MHz 8-bit DAC up to 256 colors from a total of 262,144 colors
RAM256 KB 80 ns VRAM

IBM PS/2 8557SX (link)

Year1991
Video ChipIBM 84F7985 IBMVGA256c
unknownIBM 85F0120
RAMDACINMOS IMSG171P-50
50 MHz 8-bit DAC up to 256 colors from a total of 262,144 colors
RAM512 KB 80 ns VRAM

IBM PS/2 8525SX (link)

Year1991 (?)
Video ChipIBM 84F7985 IBMVGA256c
RAMDACINMOS IMSG171P
? MHz 8-bit DAC up to 256 colors from a total of 262,144 colors
RAM512 KB 80 ns VRAM

IBM PS/2 Thinkpad 700C/720C (pic 1) (pic 2)

Year1992
Video ChipIBM 39G8600 IBMVGA256c
Clock ChipICS ICS2494
135 MHz Dual Video/Memory Clock Generator for VGA, Super VGA, XGA
video adapters, 8514A, TMS34010, TMS34020
RAMDAC? MHz on chip?
RAM512 KB 80 ns VRAM

IBM SVGA Adapter/A (link) (pic)

Year1992 (together with Server 85)
Video ChipIBM 42G3410 (= TI CF63011PCM) IBMVGA256c
unknownIBM 85F0120 (= OKI M7U016-008)
Clock ChipICS ICS2494
135 MHz Dual Video/Memory Clock Generator for VGA, Super VGA, XGA
video adapters, 8514A, TMS34010, TMS34020
RAMDACINMOS IMSG176J-80Z
80 MHz 8-bit DAC up to 256 colors from a total of 262,144 colors
RAM512 KB 80 ns VRAM


Driver Support

DOS

Generic: r700c120.exe
SVGA/A: m95svga.exe

VESA/VBE driver*

256 KB VRAM, at least 40 MHz RAMDAC 800x600 pixels, 16 colors, 60 Hz**
512 KB VRAM, at least 30 MHz RAMDAC 640x480 pixels, 256 colors, 60 Hz
512 KB VRAM, at least 40 MHz RAMDAC 800x600 pixels, 265 colors, 60 Hz**
512 KB VRAM, at least 50 MHz RAMDAC 1024x768 pixels, 16 colors, 43 Hz I***
256 KB VRAM, at least 30 MHz RAMDAC 132-column x 25-row text

Notes:

* RAMDAC requirements are calculated with the following formula:

line frequency in kHz = ([vertical resolution] * [horizontal refresh rate] Hz + [vertical resolution] * [horizontal refresh rate] Hz * 0,1)/1000

RAMDAC pixel frequency in MHz = ([horizontal resolution] * [line frequency] kHz + [horizontal resolution] * [line frequency] kHz *0,2)/1000

** the IBMVGA256c chipset does 800x600 pixels, 56 Hz too but LCDs usually don't support refresh rates below 60 Hz and you will not accept a 56 Hz refresh rate on aCRT monitor.

*** LCDs usually don't support an interlaced video resolution. 1024x768 pixels,16 colors, 60 Hz requires at least a 70 MHz RAMDAC

OS/2

From v2.11 up build in under the name "IBM VGA 256c".
640x480 pixels, 256 colors with 512 KB VRAM, at least a 30 MHz RAMDAC. A higher resolution may be possible according to THIS page.

Windows 3.1x

Generic: r700c120.exe

640x480 pixels, 256 colors w/ 512 KB VRAM, at least a 30 MHz RAMDAC together with DOS VESA/VBE software driver.


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