UMC Green CPU U5SX 486-33

The UMC 486 CPUs are somewhat oddbal CPUs. Not all 486s are identical and some really perform different. For example the Cyrix Cx486DX2/66 is slower than the Intel 486DX2/66, however, the Cyrix Cx486DX4/100GP4 is faster than the Intel 486DX4/100. The difference lies in variations in the architecture and especially L1-cache memory (write-back vs write-through).

Both Cyrix and UMC designed their 486 in-house. UMC invested in streamlining the processor and optimize the execution of instruction. This resulted in a CPU that is clock-for-clock faster than Intel. Using Doom as benchmark the UMC Super33 is faster than a Cyrix DX2/5- and almost on par with an AMD Am486DX40.

The CPU you are looking at is a soldered QFP chip on a small motherboard. It's a very low cost solution which reminds of the later 286 and 386SX motherboards. Small, an optimised chipset that doesn't need much 'glue' (chips that connect the chipset to other parts of the computer) and no fancy features in general. This motherboard is dated 1995 and only has 6 ISA slots. Remember, in 1995 a decent PC would be a 100MHz 486 or Pentium 75. In March 1995 the Pentium 120 was the fastest x86 processor money could buy.

I have an identical CPU but in ceramic: UMC Green U5SD-Super33 which I have benchmarked on a fast Biostar 8433UUD-A motherboard using a PCI S3 Virge DX graphics card.

The UMC processors are not very common. They were late to the market and UMC faced lawsuits from Intel.