derSammler wrote:

They actually had WB cache before "normal" CPUs had it.

I wouldn't take Wikipedia's word for it. Not sure who added that little nugget about the WB cache in there, but I am pretty sure that is incorrect. The POD5V63 and 83 which plugged into Socket3 on the other hand DID support write back cache...but those are Pentiums not 486s. If you can find any Intel documentation showing a 486 overdrive chip supporting WB cache I'd love to see it.

Also, I noticed there are actually three different DX2 overdrives.

ODP for SX pinout
ODP for DX pinout
ODPR for DX pinout

I guess the reason ODPR for SX pinout doesn't exist is because many OEM SX systems had the CPU soldered to the board.
As far as I know all the DX4 overdrive pinouts are of the DX type.

appiah4 wrote:

mpe wrote:

There are different versions (steppings) of the DX2 and the overdrive. That’s what creates the difference.

The only obvious difference (apart from the integrated heatsink) between any DX2 and DX2ODPR is absence of the boundary scan feature on the overdrive (apart from certain sample chips).

This is interesting, I never knew this. Are there any real world implications of this ommission?

Boundary scan is used during systems testing. The 486 chip has a number of testability pins and these don't work on production overdrive chips

https://en.wikipedia.org/wiki/Boundary_scan

DX2-66 replacement overdrives (DX2ODPR) have been produced in at least 4 different versions. The regular DX2-66 possibly in even more. Some of these might or might not have SL enhanced mode, WB L1 cache, CPUID instruction, different CMPXCHG opcode, etc. It is hard to compare DX2ODPR overdrives with regular DX2 without saying which exact versions you compare.

derSammler wrote:

From: https://en.wikipedia.org/wiki/Intel_80486_OverDrive […]
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Anonymous Coward wrote:

None of the Overdrive chips have write back cache, even as an option.

From: https://en.wikipedia.org/wiki/Intel_80486_OverDrive

Intel's i486 OverDrive processors are a category of various Intel 80486s that were produced with the designated purpose of being used to upgrade personal computers. The OverDrives typically possessed qualities different from 'standard' i486s with the same speed steppings. Those included built-in voltage regulators, different pin-outs, write-back cache instead of write-through cache, built-in heatsinks, and fanless operation — features that made them more able to work where an ordinary edition of a particular model would not.

They actually had WB cache before "normal" CPUs had it.

That article on Wikipedia is a bit misleading. Going to fix it 😀

For whoever is still interested in this topic...

I just got from Ebay an Intel 486 DX266 overdrive (DX2ODPR66) to replace my Intel DX266 (SX911) and the results are exactly the same, unless I'm missing something that CHKCPU.exe is not detecting... (I don't think so).
Landmark benchmark was the same too.
I had WB set in the BIOS but it still shows as WT as you can see in the image below.
I was tempted to remove the heat sink to see what it says but didn't pull the trigger...