Ready for a new adventure...

After I got bored playing with some late 486s processors and a Verite 3D card, I finally decided to give a go to this oddity I bought recently off eBay.

In theory one could have a Pentium 133 (OverDrive) with a VESA local bus video card and a pair of Voodoo2 all in the same rig 😳

The Opti chipset is a native VLB solution for the first generation Pentium processors. The PCI bus is controlled by a VLB bridge chip.

If anybody is interested in some data, read on.

Although I haven't been able to find the motherboard manual, at least I found how to change the clock frequency. There are two jumpers near a 14.3 MHz xtal and what appears to be some sort of PLL IC. Opening/closing them gives a total of 4 possible combinations: 40, 50, 60 and 66 MHz. At last I was able to overclock the Pentium 60 to 66MHz to do some comparisons with similarly clocked 66 MHz 486 on PCI / VLB boards.

Synthetic benches like Sysinfo or NSSI show that the CPU and the chipset are within the expected performance envelope. L2 cache is not much faster than the main memory, but I used quality 60ns DIMMs running at the fastest timings possible. Back in 1994, many Pentium system were sold with 70ns DRAM, so the difference with the cache would have been more substantial. Not to mention that this board uses 'normal' 256K 15ns chips; synchronous SRAM appeared only one year later on socket 5.

Overall, despite the bad fame of OPTi Pentium chipsets, performance is more or less in line with the offerings of the period. VLB and PCI buses, however, are an entirely different matter.

Long story short, the measured bandwidth of the native VLB bus (SPEEDSYS, VSPEED) is around 2/3 of what is found on 486 boards. PCI bandwidth, since this motherboard uses a VLB to PCI bridge, is even worse: around 50% of what similar 486 boards offer. The end result is that running benchmarks like Wolf3D or Doom results in a framerate which is not much above a 486dx2-66. Using a PCI card, the situation is even worse and I got a lower framerate than a 486DX2-66!

At least, Quake seems to be running fine, with a framerate close to that of a AMD 5x86-160. Same with VQUAKE running on a Verite V2100 PCI. Running at 15-20 fps at a resolution of 320x200, obviously Quake doesn't stress the bus enough to make the shortcomings of this chipset evident.

In the end, I believe this board was a poor choice in 1995 and not only because the writing was on the wall for socket 4. For the budget conscious gamer a 486dx4-100/120 would have been a better choice. (Quake was still one year away and it doesn't run well enough on any processor slower than a Pentium 90/100). For the power user, a Pentium 75/90 would have been a safer choice and not terribly more expensive than a Pentium 66.

Interesting. I have this board as well but I get slightly different results (though with 512kB L2 cache):

Which RAM / Cache timings do you use?

pyrogx wrote on 2024-06-15, 11:19:

Interesting. I have this board as well but I get slightly different results (though with 512kB L2 cache):
Which RAM / Cache timings do you use?

For the main RAM and L2, I'm using the fastest settings the BIOS allows. I guess having two banks of cache allows for slightly better L2 results. I prefer Write Through over Write Back because I noticed slightly better performance in some tests (not synthetic)

Been curious about these boards, great write up, thanks for sharing!

Loved my P66 Socket 4 back in the day! Beat the pants off everyone's 486s in college! 🤣

Been looking to purchase one again for a personal graphics project I'm working on.

Honestly, a P66 couldn't be beat by anything except a 486 DX4 100 in practical use in 1995.

Another interesting board that uses this chipset is also Supermicro P54VLPCI. You get Socket 5 and VLB in one go, and support for the later ceramic Pentiums. (and in theory MMX chips as well, provided you can get them working - TRW does list a Overdrive P55C for this board.)

PcBytes wrote on 2024-11-10, 11:47:

Another interesting board that uses this chipset is also Supermicro P54VLPCI. You get Socket 5 and VLB in one go, and support for the later ceramic Pentiums. (and in theory MMX chips as well, provided you can get them working - TRW does list a Overdrive P55C for this board.)

Interesting. I thought these "oddities" died out with socket 4. If this Supermicro is a Socket 5, that it would be possible to run up to a 200MHz Pentium or even on Overdrive chip. That would be the ultimate DOS gaming machine. VLB main card + Voodoo 2 on PCI

This board is also the first time I can test a VLB-PCI bridge. Performance suffers, but at least PCI cards become usable. Both in Doom and Dos Quake a ET4000W32 VLB is faster than an ET6000 PCI, so I don't see any reason why a PCI graphic card should be preferred with this motherboard, but with ISA and PCI as well, one has a lot more option when it comes to network / storage / sound cards.