Overdrives?

[H3nrik V!]

Having some odd thing for the more "oddball" processors, the Overdrives, which are a whole other chip than it actually overdrives, I got to think - has anybody made some comprehensive Overdrive testing, showing what Overdrives gives the greatest boost?

What really makes me curious are:
RapidCAD - a 486DX in 386/387 sockets. Upgrading 386 to 486 (what clocks?)
487 - not so much to discuss there - it's just a 486
Pentium Overdrive - as far as I can see, you'd go from a 486SX-33 to Pentium 83
Pentium II Overdrive - Will it give more than the actual increase in clock frequency?
Probably some x5 upgrades for 486 platform are probably also great boosts - but not so much architecture change there?

[CPUShack]

The Cyrix 5x86 was a pretty big change for the Cx486 architecturally

[Chook]

The Pentium II Overdrive also adds MMX, which the Pentium Pro didn't have.

All the Intel Overdrives were supposed to be hassle free upgrades. You could just drop them in and they would work without having to change any jumper settings. The original 486 Overdrives had a weird naming system where they were labelled the same as the chip they were supposed to replace with ODP in front of the part number. So the ODP486SX-25 was the one you bought if you had a 486SX-25. The Overdrive was in fact a DX2-50 so you doubled your clock speed and gained a math co-pro. Then there was the issue of where your Overdrive chip went. If it went in an upgrade socket beside your CPU, you got the ODP version. If your Overdrive replaced your CPU, you got the ODPR versions.
Later on Intel gave up the confusing part numbering system and labelled the chips as to what they actually were. The SX2ODP50 was the only Overdrive that really was an SX with no co-pro. All other Overdrives were DXs.
The later 486 Overdrives, the DX2-66 and the DX4-100 were very popular.

The Pentium Overdrives were not so popular, mostly because they came out so late and at such high prices that you were better off buying a new motherboard and CPU instead (which is what Intel wanted you to do, of course). The Pentium Overdrives worked best in proprietary systems that couldn't be easily upgraded. In these cases they worked well as intended - you just dropped it in and it worked. No changing any jumper settings on the motherboard. The Pentium MMX Overdrives would add MMX to systems that couldn't otherwise get it (socket 5 systems). Intel could have easily made much faster Overdrives, such as a 300Mhz one for socket 5 and 7 systems. But then, they would have been competing with their own Pentium II.

There a number of other upgrade chips made by other manufacturers that give much bigger upgrades than the Intel ones. There were adapters that let you put an AMD K6-2 on older motherboards and several upgrades based on IDT Winchips. I've also heard rumors of an upgrade adapter that lets you use a Celeron in a Pentium Pro motherboard.