rmay635703 wrote on Yesterday, 22:45:

The proprietary bus is why nobody cloned into ppro, the “pentium” bus was nothing special besides being pipelined more deeply with a longer burst cycle. The next address and burst was what was different, whether those could be handled by a simple hold and release is unknown to me.

Certain old 3rd party pentium motherboards used chipsets that stuck to 32bit memory transfers, so besides speed the chip was already being interfaced to 32 bit boards at retail

what? any info on pentium chipsets using 32bit dram? should have been as slow as pod.
i remember some people claimed opti chipsets to be the slowest for pentium, but even those boards seemed to demand two symmetric simms in a bank.

noshutdown wrote on Today, 01:23:

rmay635703 wrote on Yesterday, 22:45:

The proprietary bus is why nobody cloned into ppro, the “pentium” bus was nothing special besides being pipelined more deeply with a longer burst cycle. The next address and burst was what was different, whether those could be handled by a simple hold and release is unknown to me.

Certain old 3rd party pentium motherboards used chipsets that stuck to 32bit memory transfers, so besides speed the chip was already being interfaced to 32 bit boards at retail

what? any info on pentium chipsets using 32bit dram? should have been as slow as pod.
i remember some people claimed opti chipsets to be the slowest for pentium, but even those boards seemed to demand two symmetric simms in a bank.

I had a p60 that came with a single simm and vlb, was slow and is long since ecycled , I thought it was an UMC or OPTI but it’s been a long time.

There's an issue of PC Magazine which reviews all of the early pentium systems and lists which ones do 32/64-bit cache and main memory.
OPTi had a couple of 5V Pentium chipsets. The cheapest one supported both 486 and Pentium, and had 32-bit DRAM. They definitely supported single SIMM operation, because I had one too.

rmay635703 wrote on 2026-01-31, 00:45:

Certain old 3rd party pentium motherboards used chipsets that stuck to 32bit memory transfers, OPTi 82C571 , so besides speed the chip was already being interfaced to 32 bit boards at retail

The OPTi 82C571 was a 486 chipset that only worked with 486-to-Pentium OverDrives. It didn't work with Socket 5/7 Pentiums. All Pentium-compatible chipsets required 64bit path to memory.

Anonymous Coward wrote on Today, 02:54:

There's an issue of PC Magazine which reviews all of the early pentium systems and lists which ones do 32/64-bit cache and main memory.
OPTi had a couple of 5V Pentium chipsets. The cheapest one supported both 486 and Pentium, and had 32-bit DRAM. They definitely supported single SIMM operation, because I had one too.

Some Pentium motherboards allowed the system to boot with a single SIMM installed, but this does not mean the memory bus was 32-bit. The chipset still had a 64bit memory bus. A single SIMM populated only half the bus as a degraded, fallback operation (interleaving disabled, half bandwidth). This is not the intended configuration. Intel's own documentation for the 430FX and 430VX chipsets explicitly describe the degraded mode.

So yeah, you could run a Pentium with a single SIMM but the chipset itself still provided a 64bit path to memory. But no chipset was designed to work with both 486 and real Pentium class chips in 32bit memory mode.

feipoa wrote on Yesterday, 14:19:

OzzFan wrote on 2026-02-10, 17:33:

I'm also not quite sure why Intel's offering was referred to as "shitty" either. For what it was, I think it is an excellent product.

Probably because very few socket 3 motherboards worked with the POD when L1 was in write-back mode. Has anyone made a list? I'd be surprised if it topped more than a dozen motherboards. I can only think of 3.

That just means loss of performance while running in write-through mode. That doesn't make the chip shitty. It's a workaround for boards that don't support write-back mode.

OzzFan wrote on Today, 14:12:

Anonymous Coward wrote on Today, 02:54:

There's an issue of PC Magazine which reviews all of the early pentium systems and lists which ones do 32/64-bit cache and main memory.
OPTi had a couple of 5V Pentium chipsets. The cheapest one supported both 486 and Pentium, and had 32-bit DRAM. They definitely supported single SIMM operation, because I had one too.

Some Pentium motherboards allowed the system to boot with a single SIMM installed, but this does not mean the memory bus was 32-bit. The chipset still had a 64bit memory bus. A single SIMM populated only half the bus as a degraded, fallback operation (interleaving disabled, half bandwidth). This is not the intended configuration. Intel's own documentation for the 430FX and 430VX chipsets explicitly describe the degraded mode.

So yeah, you could run a Pentium with a single SIMM but the chipset itself still provided a 64bit path to memory. But no chipset was designed to work with both 486 and real Pentium class chips in 32bit memory mode.

Sis 5571 could operate like that I believe. Not sure if intel chipsets supported it though. The opti budget chipsets we’re definitely not 64 bit though, and it’s clearly stated in the brochure which is on bitsavers.

https://bitsavers.org/components/opti/brochur … ochure_1993.pdf

Anonymous Coward wrote on Today, 15:43:

OzzFan wrote on Today, 14:12:

Anonymous Coward wrote on Today, 02:54:

There's an issue of PC Magazine which reviews all of the early pentium systems and lists which ones do 32/64-bit cache and main memory.
OPTi had a couple of 5V Pentium chipsets. The cheapest one supported both 486 and Pentium, and had 32-bit DRAM. They definitely supported single SIMM operation, because I had one too.

Some Pentium motherboards allowed the system to boot with a single SIMM installed, but this does not mean the memory bus was 32-bit. The chipset still had a 64bit memory bus. A single SIMM populated only half the bus as a degraded, fallback operation (interleaving disabled, half bandwidth). This is not the intended configuration. Intel's own documentation for the 430FX and 430VX chipsets explicitly describe the degraded mode.

So yeah, you could run a Pentium with a single SIMM but the chipset itself still provided a 64bit path to memory. But no chipset was designed to work with both 486 and real Pentium class chips in 32bit memory mode.

Sis 5571 could operate like that I believe. Not sure if intel chipsets supported it though. The opti budget chipsets we’re definitely not 64 bit though, and it’s clearly stated in the brochure which is on bitsavers.

https://bitsavers.org/components/opti/brochur … ochure_1993.pdf

That brochure is from 1993, the same year the original Pentium 60 & 66MHz chips were released. I see no evidence that an actual motherboard was made for both Socket 2/3 486 and Socket 4/5 Pentiums were actually made. OPTi was probably working from limited or inaccurate data from Intel at the time. The best explanation is that the brochure was referencing the then-upcoming 486-to-Pentium OverDrive and not a true Pentium chip.

While rare, they do exist. TMC/MyComp seemed to have a special affinity for them.

https://theretroweb.com/motherboards/s/tmc-my … p-mynix-pat45pv

Enjoy.

Anonymous Coward wrote on Today, 16:35:

While rare, they do exist. TMC/MyComp seemed to have a special affinity for them.

https://theretroweb.com/motherboards/s/tmc-my … p-mynix-pat45pv

Enjoy.

Ok, I stand corrected on that point, however, it only supports Socket 4 Pentiums which were clocked slower than the 486-to-Pentium OverDrive. From the documentation I'm reading, the Socket 4 Pentiums could run with a 32bit memory subsystem, but Intel was quick to abandon Socket 4 in favor of Socket 5.

Which brings us all the way back to the original statement: why didn't CPU upgrade manufacturers produce a faster speed Pentium for 486 systems? Because the faster variations would not work with 486 class chipsets. That statement still holds true.

Intel actually did have plans for a faster POD for 486 systems. I believe it was to be a 100Mhz model, but it was cancelled because the market already moved on.

Also I want to say that at least one socket5 motherboard uses that dreadful opti 571/572 chipset. There were also boards made with similar crappy chipsets from UMC and Forex.