First post, by DonutKing
I have recently tracked down a Socket 4 motherboard and Pentium 60. I decided to put it through the paces and compare it to a much more common system of the era - a 486.
I've always been a bit curious about the original Pentium as released in 1993 - it was a bit of a strange beast at the time. The processors were expensive and ran very hot, requiring a noisy fan; the motherboards were difficult to manufacture since they used a 60MHz/66MHz bus (most 486's used 33MHz at the time), and it had a funny name. Socket 4 didn't have a very long run in the marketplace either; Socket 5 came out about a year or so later which was when it started becoming a more popular system for home users. Socket 5 ran the processors at 3.3V instead of 5V so they were much cooler, and also at higher clockspeeds. The end result was that Socket 4 systems were very expensive and quite rare.
Here are a couple of pictures showing, from left to right, a Socket 7 Pentium 233MMX; a Socket 5 Pentium 90; and a Socket 4 Pentium 60.
Here you can see the physically larger size of the socket 4 processor, and its standard pin grid array, compared to the staggered pin grid array of the newer processors.
Note the integrated heatsink and fan on the MMX - I believe 'boxed' processors came with these, as opposed to processors supplied on a tray to OEMs who may want to use their own cooling solution. There were also some Pentiums in the standard flat ceramic package.
Socket 5 and 7 were very similar- Socket 7 had one extra pin and the motherboards were backwards compatible with Socket 5 processors - but socket 7 processors had special voltage requirements and generally wouldn't work in a Socket 5 board. Most people who owned a Pentium had a Socket 5 or 7 system.
On to the motherboard. This is an Acer V12P socket 4 board, with 256KB of L2 cache. It uses the Intel 430LX chipset, which was the first chipset for the original Pentiums. Seems to be about a mid 94 build date judging by the date of the IC's so this is probably a very late socket 4 board. Interestingly it uses a socketed crystal oscillator to set its bus speed, rather than jumpers like many 486 boards do. Currently it has a 60MHz crystal installed. If I had some spare crystals I could try overclocking it although I doubt I'd be able to squeeze much more out of it. I do have an 80MHz crystal in my 386DX40 but I seriously doubt I'd get 80MHz out of this Pentium, especially with no voltage adjustment.
It's a pretty standard looking board really. Being an Acer there aren't many options to tweak in the BIOS.
One of the interesting things about the early Pentium was the FDIV bug. You can read about it here but basically in certain circumstances, performing division operations on the floating point unit would cause incorrect results. In practice it was unlikely the majority of users would run into this bug but Intel eventually agreed to replace the affected processors on request, which cost them $500 million. Some comparisons can be drawn between the recent Sandy Bridge motherboard recall and the FDIV bug recall nearly 20 years ago 😀
Since processors with the FDIV bug are pretty rare nowadays, I was eager to discover if the CPU I had was an affected model. I downloaded a utility called PENTBUG.EXE which would check for the bug:
As you can see this processor is a fixed model and doesn't have the bug. Kind of disappointing (ironically that's probably the opposite reaction most people who ran this utility would have 😜 ) Ignore the blue tinge, my monitor cable is a bit dodgy 😜 Interestingly, the Pentium 90 in the pictures above is S-Spec SX879 which supposedly has the FDIV bug; one day I might fire it up and confirm.
Anyway, I was curious to find how it performed. I fitted it with an S3 Virge DX PCI video card, 2x 16MB 60ns RAM and a Quantum Fireball 1280AT with DOS 6.22 and some benchmarks installed.
I have also benchmarked it against one of my other DOS boxes, a 486DX4 100MHz, on a UM881OP-AIO motherboard (UMC chipset). These systems were available at roughly the same time although the 486 CPU and motherboards were significantly cheaper. I used the same RAM, video card and hard disk on both systems.
Here are the results:
Interestingly, for the average DOS game it appears the cheaper and more common 486DX4 is pretty much on par with the Pentium 60. 3Dbench actually favours the 486 by a significant amount.
PCPbench in SVGA mode gives the Pentium the advantage, but neither are particularly brilliant scores. I tried to play Tie Fighter in SVGA mode on the 486 some time ago and it was nearly unplayable; standard VGA mode was a much more enjoyable experience. I doubt the Pentium 60 would be significantly better in this regard- I would have liked to test this but without some sort of benchmarking tool it would be hard to quantify the difference, plus I haven't had time to do so 😒
The general consensus seems to be that you really need a much faster system, probably over 100MHz for SVGA mode in games to be viable.
PCPBench seems to be a much 'busier' benchmark than 3Dbench, with more polygons and textures etc, so I can see how the higher raw integer performance of the Pentium would be an advantage here, as would the faster FSB (60MHz vs 33MHz for the 486).
Norton Sysinfo's synthetic CPU benchmark shows the Pentium to have close to twice the raw performance of the 486 despite the 486 running at about 50% faster clockspeed.
Doom is the most interesting one to me - it shows that for the average DOS VGA game there is very little separating the two systems.
Later games that used the Quake engine would probably favour the Pentium I'd imagine, as it made heavy use of floating-point instructions- the Pentium has a much stronger floating point unit than the 486. Some say Quake's code was specifically optimized for the Pentium as well. If there is enough interest and I get time I may try to run a Quake benchmark on both systems, however keep in mind that Quake wasn't released until 1996 and I consider it part of a different era in computing. By 1996 Windows 95 was out, and Socket 7 Pentiums were available in clockspeeds over 100MHz.
The interesting thing to keep in mind here is that the 486 motherboard can be upgraded with an AMD 133MHz 5x86 CPU, while Socket 4 was very much a dead end (to upgrade to a Pentium 75 or faster you needed a new, socket 5 motherboard). The AMD 5x86 came out about a year later than the DX4 or Pentium 60 but was significantly faster than the 486DX4 - it was even marketed as being equal to a Pentium 75. Unfortunately I don't have such a CPU to benchmark with but I'm certain it would be a noticeably faster system than either of those benchmarked here.
So, overall, the Socket 4 Pentium isn't much more than a curiosity - you'd be better off with a 486 for VGA DOS games, or a later Pentium for SVGA or Win9x games. Even in 93/94 it seems you would have been better off sticking with a 486.