This is an SMD package CPU mounted on a PGA board to fit into a standard desktop socket.

Great little sub-unit this! Overclocked it to 40MHz no probs. Used it for years and years. No heatsink needed at 40 either! Not bad for a so-called -25.

Not a real co-processor. This is really just an i486DX in redesigned packaging that, when installed, would disable the onboard i486SX and take over main operation of the CPU/FPU.

Please note, this chip has one-more-pin than a true i486DX chip. It works as a kind of "disable the other guy" pin. This was to facilitate end-user installation, without first removing the system-manufacture's supplied CPU. ie. what end user can remove a PLCC or indeed a PQFP surface mounted chip. The A80486SX "cripple-chip" commonly came in PLCC and PQFP confugurations as often as it came in PGA! Please note, the i486SX "cripple-chip" has the same pins as the true i486DX chip, and are thus pin-for-pin, same-for-same (assuming equal clock).

One of the earlier Pentium 60s, a B1 stepping model. These models suffered from heat troubles and where therefore enhanced with a heat spreader, a flat metal plate designed to distribute heat evenly across the processor surface, in later models of the P5. This item here had a huge cooler mounted on top (which was not easy to unmount ;-). Of course it features the infamous FDIV bug.