486-era Synthetic CPU Benchmarks

To provide some rough guidance on comparing 486-era (Socket 3) CPUs, the chart below illustrates typical SpeedSys scores for a variety of processors from Intel, AMD and Cyrix. Since IBM, Texas Instruments and ST were authorised rebrands of Cyrix processors, you can use the closest Cyrix chip for reference.

The version of the DOS SpeedSys synthetic benchmarking utility used to gather these results was v4.75.

Note that this is a synthetic benchmark (not based on real-world tests) - results can vary when compared to other seemingly identical CPUs, due to the motherboard design and other components that make up the tested system. As such, do take these figures with a pinch of salt.

AMD's Am5x86, despite using "Pentium rating" values on the chip name like "P75", were still very much a 486 core - they were just hardcoded with a clock multiplier of 4x. The fastest of these is the one in the chart above, which runs at 133 MHz - this chip could run on *any* 486 motherboard that supported a 3.3V CPU (or use a voltage regulator if not), even those that had no capability of clock doubling or tripling - that's not all, but it also had twice the L1 cache (16 KB) that an Intel 486 had (8 KB).

The IBM 5x86C rules the roost on the Gen 1-4 performance scale with a Speedsys score of 55 for the 100 MHz variant - this is just shy of an Intel Pentium 75 Speedsys score. Packaged like a 486 so it could be used as an upgrade on existing 486 motherboards, its internals featured some of Cyrix' upcoming 5th generation core, codenamed "M1". It also had twice the Level 1 cache (16 KB) of an Intel 486. The fastest version of the Cyrix/IBM 5x86C was 133 MHz, though these are very rare. Should you find one, performance is similar to a Pentium 100. The 5x86C-100 is rumoured to be very overclockable - up to 150 MHz is not uncommon, which puts CPU performance up there with a Pentium 120. Of course the downside of these Cyrix/IBM processors is finding a motherboard that will support them.