Marco Pistella wrote on Yesterday, 14:04:

For comparison purposes it would be very useful to repeat Command 4 on 800×600 and 1280×1024 with the original unmodified BIOS […]
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For comparison purposes it would be very useful to repeat
Command 4 on 800×600 and 1280×1024 with the original
unmodified BIOS, if you still have access to it. That would confirm whether the jitter is BIOS-induced or
hardware-specific.

I have lost original bios. Not really looking forward to experiment with downloaded ones.
However I have similar PowerColor Radeon 9600 Pro (RV350) with orig BIOS. So I put it into same PC. Please note that I have CRT monitor - Samsung SyncMaster 765mb in case it plays any role.

Falcosoft wrote on Today, 08:01:

@Marco Pistella: Do 64-bit reads/writes use FPU or MMX registers?
BTW, I very much like your test program 😀 I think this is the only available DOS tool that can measure such high bandwidths reliably.

Thank you — and glad you find it useful!

To answer your question: 64-bit reads and writes use FPU
registers via x87 (fild/fistp). MMX is intentionally not
used, to maintain compatibility with systems without MMX
support. The finit instruction can introduce significant
overhead on some CPUs, which may explain the 64-bit
anomaly you observed.

To investigate further: use the cursor keys to navigate
to the overhead screens in the benchmark results. These
show the routine overhead in PIT cycles for each access
width and allow a more accurate interpretation of the
raw numbers — particularly for the 64-bit case where
finit overhead may be the dominant factor.

vutt wrote on Today, 09:13:

I have lost original bios. Not ... [CUT]

Thank you for the comparison with the original BIOS —
this is exactly the kind of controlled test that helps
isolate the cause of the anomalies seen earlier.

The pattern is irregular and the values are still high for a card
of this generation — which suggests the issue may
not be entirely BIOS-related.

To investigate further, could you press D on the
timing screen for each mode to display the horizontal
frequency sample distribution, and post the screenshots?
The shape of the distribution will help understand
whether the jitter has a specific pattern or is random
noise.