Local bus is local bus. Whether the chip is connected to the CPU via a card or soldered directly on the motherboard, with same CPU and same configuration, performance will be identical. Unless you need the 2MB of RAM and there's no expansion option onboard there is absolutely no benefit to adding a card with the same chip as onboard.

As for benchmarks - you're comparing benchmarks on completely different systems. Thandor's benchmarks are on a Pentium 100, Retronn.de doesn't mention the CPU but does state that the VLB is running at the high and non-standard speed of 42MHz. Your system currently has a 486 running at 25MHz with VLB running at 25MHz. I'd be very careful about drawing any conclusions on where bottlenecks would be based on these very dissimilar ones.

You don't mention which operating system(s) you intend to run, but reading Doom I assume DOS. Basically, DOS and DOS programs don't do anything with advanced features of a VGA chip and performance is - if not CPU limited - purely a measure of how fast the card can fill the framebuffer. This is heavily dependent on bus speed (VLB) and bridge efficiency (PCI). So in DOS, some very simple designs get best performance, but the differences are tiny. You only see a couple of chips/cards slow things down because they themselves become the bottleneck - as you can see in the Retronn.de benchmark: at VGA resolutions and colour depths there is hardly any difference between the old 805 and much newer 968 (in fact the 805 wins on writes, because if you don't use its dual-porting, VRAM is slower than DRAM). Bump it up to higher resolutions and colour depths and the 968's 64b memory bus allows it to pull ahead from the 805's 32b memory bus with slow clocks. However the difference is small at 8bpp, so a 32b design with faster clocks might beat it (indeed, the fastest two VLB chips I've found under DOS, the Ark Logic 1000VL and UMC 418AF both have 32b buses). More than 8bpp isn't relevant for DOS gaming.

Thanks for taking the time to look into this, that's very helpful. It's clear that there is not much to gain with buying the 805 card, so I can put that to rest.

Very interesting part about DOS performance! I'm indeed building this system to play DOS games. From what I see, games requiring windows 95 or running at higher resolutions (let's say the win95 version of Red Alert) generally seem to need a decent Pentium to run right. As VLB is mainly found in 486 systems it makes me wonder; what do you actually use high end VLB cards for? From your story I would think I'm best off sticking to my 805 and upping the bus speed a bit.

Blavius wrote on 2023-01-08, 10:11:

Thanks for taking the time to look into this, that's very helpful. It's clear that there is not much to gain with buying the 805 card, so I can put that to rest.

Very interesting part about DOS performance! I'm indeed building this system to play DOS games. From what I see, games requiring windows 95 or running at higher resolutions (let's say the win95 version of Red Alert) generally seem to need a decent Pentium to run right. As VLB is mainly found in 486 systems it makes me wonder; what do you actually use high end VLB cards for?

You're thinking in 2023. Think in 1995 instead. A year ago you bought a very expensive 486DX2-66 system with VLB. You don't intend to buy a new PC for another 3 or 4 years (Dutch PC Prive fiscal incentives at the time only allowed one once every 5 years). But this new Windows 95 runs like crap on your old S3 805. An S3 968 Windows accelerator would probably massively improve that without having to buy a new PC. Hey presto, there's your use case for these cards.

From your story I would think I'm best off sticking to my 805 and upping the bus speed a bit.

That will instantly improve performance in an almost linear fashion. Possibly your current 486SX-25 will run reliably at 33MHz.

Possibly your current 486SX-25 will run reliably at 33MHz

A lot of 25 Mhz 486's run at 33 MHz without any issues (I would even say, that most should do).
Some have even made it at 40 MHz (you need to install a heatsink if CPU starts at this frequency, it becomes really hot soon).

Basic rule (to the 5 Volt 486):
DX-33 and below: Nothing
DX-40, DX2-50: Heatsink
DX-50, DX2-66, DX2-80: Heatsink + Fan

dionb wrote on 2023-01-08, 11:08:

You're thinking in 2023. Think in 1995 instead. A year ago you bought a very expensive 486DX2-66 system with VLB. You don't intend to buy a new PC for another 3 or 4 years (Dutch PC Prive fiscal incentives at the time only allowed one once every 5 years). But this new Windows 95 runs like crap on your old S3 805. An S3 968 Windows accelerator would probably massively improve that without having to buy a new PC. Hey presto, there's your use case for these cards.

So, mainly from a nostalgic sense then? I get that, I use a lot of hardware just because I had it back in the day, not because it the best out there. But you would end up with a system with a relatively underpowered cpu. Concretely, what could you comfortably still do then? Maybe Sim City 2000 in a higher resolution?

phantom_pl wrote on 2023-01-08, 11:18:

A lot of 25 Mhz 486's run at 33 MHz without any issues (I would even say, that most should do).
Some have even made it at 40 MHz (you need to install a heatsink if CPU starts at this frequency, it becomes really hot soon).

The board I have is also used in models with 33MHz bus. In the manual for my machine IBM states you can use a DX-33 and DX2-66 by swapping out the crystal. So it is definitely designed for 33MHz operation. In fact, I tried and it works fine, the DX2-50 I had in there now runs at 66MHz without even getting warm.

I'm wondering about 40MHz though. I could avoid heat and stress on the cpu by using a 5x86-133 at 3x multiplier (3x40=120), but what about the rest of the components? If it doesn't run stable, okay, i'll just put it back to 33MHz. But is there a risk of breaking things?

Blavius wrote on 2023-01-08, 12:26:

I'm wondering about 40MHz though. I could avoid heat and stress on the cpu by using a 5x86-133 at 3x multiplier (3x40=120), but what about the rest of the components? If it doesn't run stable, okay, i'll just put it back to 33MHz. But is there a risk of breaking things?

Most 5x86-133 run stable at 4x40 = 160.
First it is a bit of work to find out a setup that runs memory & cache timings stable at 40 MHz. I can run 2-1-1-1 with L2 cache in 2 banks.
Second is to find out which components make troubles with 40 MHz FSB, most likely PCI cards or IDE adapter. Some boards support a PCI divisor of 2/3, leading to 27 MHz. On my graphics card it is the AGP-to-PCI-brigde chip which needs a cooler at 40 MHz PCI clock. If you add PCI components that can deal with 66 MHz PCI, you may not face problems at all.

I wouldn't worry too much about your onboard 805 missing the second megabyte. It seems to me that unless you had the 805i version that supports memory interleaving paired with a beefier RAMDAC, anything that used the 2MB would be too slow to be useful.

Blavius wrote on 2023-01-08, 12:26:

[...]

So, mainly from a nostalgic sense then? I get that, I use a lot of hardware just because I had it back in the day, not because it the best out there. But you would end up with a system with a relatively underpowered cpu. Concretely, what could you comfortably still do then? Maybe Sim City 2000 in a higher resolution?

The killer app for those cards was Win3.1 desktop with Office 6.0 or Windows 95 with Office 97. The few Windows-based games might be able to use higher resolutions but rarely use more colours. These are Windows desktop accelerators, sometimes with CAD-features. Not games. The only VLB card aimed squarely at gaming was the Creative 3DBlaster.

Games stayed CPU-limited until they started getting natively accelerated too, which basically didn't happen with VLB cards - and no 486 CPU would be able to run those games decently either.

Hello,

I would suggest you forget about the graphics and upgrade the CPU.
If you can have external 33MHz, then upgrade to a DX2-66, that will be a huge jump from an SX-25!

EDIT: Sorry, I overlooked that you did that already 😁

Fine, then. Yes, AM5x86 would be better, but I guess you don't have 3volts support. And still if you have an 3 volts adapter it is unlikely that the board will work correctly with it.
So I would stick to 66MHz, that is the easist option.

CoffeeOne wrote on 2023-01-08, 19:52:

Fine, then. Yes, AM5x86 would be better, but I guess you don't have 3volts support. And still if you have an 3 volts adapter it is unlikely that the board will work correctly with it.
So I would stick to 66MHz, that is the easist option.

No, I don't unfortunately. On my 76i there is a header to plop in a VRM, but this one is 5volt only. I'm looking into a voltage interposer, but until then it's going to be 66MHz, as overdrive processors with built-in converters like the DX4 and the POD are just way too expensive these days.