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Am486DX4 "Plus"?

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First post, by torindkflt

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Alright, a Google search is revealing nothing, so I thought I'd ask here. I'm in the process of recreating a computer system from my childhood. I've managed to reach a point now where I'm able to begin doing some power-on tests. The childhood version of this system had an AMD 486DX4-100 processor, and thus I ordered one from eBay to use in the recreation. However, a curiosity has arisen.

According to the POST status screen, the processor installed is an "Am486DX4-Plus". I do not recall the childhood system stating the "Plus" portion, rather instead it simply stated "Am486DX4". What exactly does the "Plus" mean? The processor itself doesn't have "Plus" printed anywhere on it, nor any other indication as to what it could mean.

The motherboard is a QDI V4P895GRN/SMT V1.0 S1.1 (Almost identical to the childhood original, only difference is the original was "S1.0"). Here's a picture of the processor itself and the POST status screen:

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I'm also a little concerned at the fact that it reports no math coprocessor installed. All 486DX and higher processors have them built-in, do they not? Could this perhaps be the "Plus" aspect of it? If so, I don't see how that could be a plus...rather it's a detriment!

Unfortunately, I do not currently have a working AT keyboard nor drive controller card, so I am not able to enter CMOS setup or do any further testing beyond this point. Hopefully soon, but purchasing additional components shall need to wait until I have better funds available.

Thank you.

Reply 1 of 5, by smeezekitty

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It just looks like a regular Am486-100 to me. I wouldn't worry about what the BIOS says.
It is a writeback chip. Maybe it has something to do with that?

You will really need to get a keyboard to do anything more with it.

Reply 2 of 5, by jesolo

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Refer to the attached links for more information:
http://www.cpu-collection.de/?l0=co&l1=AMD&l2=486%20DX
http://en.wikipedia.org/wiki/Am486

The more common CPU's were the ones that had write through level 1 cache. AMD later introduced the "enhanced" or "plus" CPU's with write back level 1 cache and power saving features.
The particular one that you pictured is the DX4-100 with 8 KB level 1 write back cache. It's slightly faster than the equivalent write through CPU.

You can buy an AT 5-pin DIN to PS/2 keyboard converter and then use a standard PS/2 keyboard (if you still have a PS/2 keyboard lying around).

When you get into the BIOS, I suggest resetting everything to its factory default settings, save and restart and go into the BIOS again to then optimise your settings.
This includes setting your cache cycle times, making your system and video BIOS cacheable, etc. Just make sure that, if available, you set the level 1 cache scheme of the CPU to write back and that it is enabled.
Also, make sure the jumper settings on your motherboard is correct (from the POST screen, it appears so).

Reply 3 of 5, by noshutdown

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amd 486dx2/dx4 had 3 types of cache setup: 8kb wt, 8kb wb, and 16kb wb, from oldest to newest. your model is 8kb wb version.
according to amd datasheet, models with 16kb wb is officially called "enhanced 486dx2/dx4", while models with 8kb wb is officially called "486dx2/dx4 with write back cache".

Reply 4 of 5, by Robin4

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Does your QDI V4P895GRN/SMT V1.0 S1.1 board have a VRM?? Because now it would running on 5volts.. The cpus needs 3 volts! Running it to long in 5volt will burn your cpu to death.

~ At least it can do black and white~

Reply 5 of 5, by torindkflt

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It has a jumper to select between 5v and 3.3v, and it was already configured for 3.3v when I received it. Also, I realize the CPU is inserted wrong in the picture, as beforehand I had swapped in a DX2-66 for testing purposes. I made sure to correct that oversight before powering it on.

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