-Could it be that the 64bit memory bus is only enabled under Windows with drivers loaded for GUI acceleration?

That was my suspicion. Though it migh also help in VESA 2.0 modes using an LFB. Do try to enable writing combining (with fastvid, for example).

If running Windows 3.x or even 9x , maybe you could try Steve Gibson's Torque utility/benchmark .

Scitech Display Doctor/UNIVESA/UNIVBE has a utility that can run dome benchmarks (vbetest, ,AFAICR).

-Am I wrong to expect a performance increase with 2MB for this card?

I'm not sure you'll get performance increase, but the list of available resolutions will be larger.
With only 1 MB you can get 640x480 in 24-bit color, but 800x600 only in 16-bit color, and 1024x768 only in 256 colors.
2 MB gives you 800x600 in 24 bpp and 1024x768 in 16 bpp.

darry wrote on 2024-05-14, 08:14:

That was my suspicion. Though it migh also help in VESA 2.0 modes using an LFB. Do try to enable writing combining (with fastvi […]
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-Could it be that the 64bit memory bus is only enabled under Windows with drivers loaded for GUI acceleration?

That was my suspicion. Though it migh also help in VESA 2.0 modes using an LFB. Do try to enable writing combining (with fastvid, for example).

If running Windows 3.x or even 9x , maybe you could try Steve Gibson's Torque utility/benchmark .

Scitech Display Doctor/UNIVESA/UNIVBE has a utility that can run dome benchmarks (vbetest, ,AFAICR).

Yeah that's my conclusion too, unless of course the chipset feature is broken on this specific card. I was never able to get a performance increase no matter what I tried in dos (eg. fastvid), windows XP, or dos software under XP. Admittedly I can't speak about windows 3.x or 9x with their own drivers, I was only trying to see if it's an undercover/little known dos performer. Well I can't complain, I have my results: It's not 😁

konc wrote on 2024-05-16, 10:07:

darry wrote on 2024-05-14, 08:14:

That was my suspicion. Though it migh also help in VESA 2.0 modes using an LFB. Do try to enable writing combining (with fastvi […]
Show full quote

-Could it be that the 64bit memory bus is only enabled under Windows with drivers loaded for GUI acceleration?

That was my suspicion. Though it migh also help in VESA 2.0 modes using an LFB. Do try to enable writing combining (with fastvid, for example).

If running Windows 3.x or even 9x , maybe you could try Steve Gibson's Torque utility/benchmark .

Scitech Display Doctor/UNIVESA/UNIVBE has a utility that can run dome benchmarks (vbetest, ,AFAICR).

Yeah that's my conclusion too, unless of course the chipset feature is broken on this specific card. I was never able to get a performance increase no matter what I tried in dos (eg. fastvid), windows XP, or dos software under XP. Admittedly I can't speak about windows 3.x or 9x with their own drivers, I was only trying to see if it's an undercover/little known dos performer. Well I can't complain, I have my results: It's not 😁

There are some PCI registers that you could check to see if 64-bit memory access is enabled and possibly how to enable it (by writing proper values into these registers).
Maybe the VBIOS is expected to set them and somehow isn't doing it ? Or maybe they are implicitly set if 2MB of memory is detected and there is just not a significant performance difference .

Source : https://dn790008.ca.archive.org/0/items/bitsa … l_4ed_Feb95.pdf

darry wrote on 2024-05-17, 03:00:

There are some PCI registers that you could check to see if 64-bit memory access is enabled and possibly how to enable it (by writing proper values into these registers).

I found the idea fascinating and decided to explore it, hence the late reply. So after dusting off my C skills,

1MB default configuration soldered on the card: As expected from the data sheet (bit 3 disabled, bit 4 enabled)

2MB: the register's bit is set internally and automatically when the memory is expanded (bits 3 & 4 enabled). So the 64-bit memory data bus does get enabled!

Since we are it, what about bank switching (bit 7)? It shouldn't matter but let's enable it too...

Yeah still no difference. So, it appears that the 64-bit memory data bus is enabled with 2MB of VRAM, but it makes exactly zero performance difference under DOS. Not even a tiny one within the small margin of repeated tests, the numbers of 4 different benchmarks are exactly the same to the decimal digit. Now that it's confirmed that the bus width changes correctly when expanding the memory, maybe it makes sense to test with 1. a much less powerful system and 2. in windows 3.x/9x with drivers installed.

Anyway, I had a great time tinkering with this, which was the reason I got the card in the first place. And I'm left with my own DOS software to manipulate registers 😁

konc wrote on 2024-05-21, 08:47:

I found the idea fascinating and decided to explore it, hence the late reply. So after dusting off my C skills, […]
Show full quote

darry wrote on 2024-05-17, 03:00:

There are some PCI registers that you could check to see if 64-bit memory access is enabled and possibly how to enable it (by writing proper values into these registers).

I found the idea fascinating and decided to explore it, hence the late reply. So after dusting off my C skills,

1MB default configuration soldered on the card: As expected from the data sheet (bit 3 disabled, bit 4 enabled)
1MB.png

2MB: the register's bit is set internally and automatically when the memory is expanded (bits 3 & 4 enabled). So the 64-bit memory data bus does get enabled!
2MB.png

Since we are it, what about bank switching (bit 7)? It shouldn't matter but let's enable it too...
2MB_2.png

Yeah still no difference. So, it appears that the 64-bit memory data bus is enabled with 2MB of VRAM, but it makes exactly zero performance difference under DOS. Not even a tiny one within the small margin of repeated tests, the numbers of 4 different benchmarks are exactly the same to the decimal digit. Now that it's confirmed that the bus width changes correctly when expanding the memory, maybe it makes sense to test with 1. a much less powerful system and 2. in windows 3.x/9x with drivers installed.

Anyway, I had a great time tinkering with this, which was the reason I got the card in the first place. And I'm left with my own DOS software to manipulate registers 😁

Thank you for testing and for sharing the results. I tend to use RWEverything or just the plain DOS Debug utility to manipulate registers (not that I often need to), but that's just because I'm not a programmer. Custom DIY stuff is always cool.