AMD's DX4 ?

Don't have any experience with your PS/1.

However, I'd be surprised if it's the cache that's the problem. It's usually something else (voltage, type of socket, bus speed...).

Which PS/1 model do you have, what's it's current CPU and which DX4 did you try?

The Intel DX4-100 is a 3.3V CPU and was released in 1994 (unless, you have an Overdrive 486 CPU).
The IBM PS/1 was released in 1990 and already discontinued in late 1994.
Chances are that the motherboard only supports 5V CPU's and neither would the BIOS (check for a voltage regulator on the motherboard).

I have a voltage regulator for the 3,3v. I do not remember the site where I found the discussion in which there was talk of the incompatibility of the PS / 1 with the CPU at 16kb but I remember reading it.

i have this cpu http://www.cpu-world.com/CPUs/80486/AMD-A8048 … X4-100NV8T.html but i not know if is the fastest with the required 8kb

It's not the size of the cache, actually. The problem is that all 486 CPUs with 16 kb L1 cache are using Write Back mode for it, unless you change it to WT in the BIOS (which you can't, since the BIOS does not know about it).

The original AMD DX4 (not the enhanced one) should work just fine when using a converter for 3.3V.

derSammler wrote:

The problem is that all 486 CPUs with 16 kb L1 cache are using Write Back mode for it, unless you change it to WT in the BIOS (which you can't, since the BIOS does not know about it).
.

This is not accurate. Intel DX4 with 16kB L1 CPU's can be either WB or WT (they have slightly different model number engraved on the top). DX4 overdrives are always WT.

More than BIOS settings it is a matter of wiring WB pins to the chipset. Many non-WB chipsets are ignoring/not-wiring those pins and even the WB CPU runs in WT mode. Yes some weird chipsets can be confused by those pins.

AlessandroB wrote:

I have a voltage regulator for the 3,3v. I do not remember the site where I found the discussion in which there was talk of the incompatibility of the PS / 1 with the CPU at 16kb but I remember reading it.

Can you post a picture of it?

Chances are that if WB is indeed the issue, one of jumpers can float the WB/WT pin.

mpe wrote:

This is not accurate. Intel DX4 with 16kB L1 CPU's can be either WB or WT (they have slightly different model number engraved on the top).

These were available to OEMs only. I don't count them. When the retail DX4 arrived in October 1994, even the DX2 got WB cache.

derSammler wrote:

mpe wrote:

This is not accurate. Intel DX4 with 16kB L1 CPU's can be either WB or WT (they have slightly different model number engraved on the top).

These were available to OEMs only. I don't count them. When the retail DX4 arrived in October 1994, even the DX2 was switched to WB cache.

I guess 25 years later we don't need to care too much about which CPUs were available through which sale channel. DX4 can be had in either version, so you can't say they are all WB. Arguably, without making any statistics, nowadays on eBay by observation WT models seems to be just as common as WB. Is it because people are breaking up more OEM PCs?

In fact weren't all non-overdrive IntelDX4's OEM only?

Anyway, the OP can have either version of DX4. I have them all 😀

Even WB CPUs support WT, this is set by state of one pin during reset and that pin is generally set so that on a board that doesn't support WB the CPU starts in WT mode.

I have an IBM PS/1 and it does work with Intel 486dx4-100 Overdrive CPU in primary CPU socket. Not the overdrive CPU socket.
You need to set the jumper settings.
By default most basic IBM PS/1 came with the Intel 486sx-25mhz
So you need to change the jumpers or 33mhz.
Use 486dx2-33 setting also

The Intel overdrive 486dx4-100 will work with these settings.

There are several IBM PS/1 versions ( about 5 or 6 )
that have different CPU's and motherboards.
If you have the base model with a 486sx-25mhz CPU and an overdrive socket then the best you can do is to insert an Intel overdrive 486dx-33 or 66
both of which will run at 66mhz even though one is labled 33 it actually runs at 66mhz.
But you need the overdrive CPU with 169 pins. It has an extra pin in the center edge of the CPU.
So look carefully for the Intel overdrive CPU with the extra pin.

So if you are using the primary CPU socket then a regular 168 pin Intel Over drive CPU will work. ( 486dx4-100mhz max )
If you are using the Overdrive socket then you need an Intel Overdrive 169 pin CPU. ( best you can do is 66mhz )
AMD 5x86 CPU's will not work.

link
486 Overdrive CPU's - Intel and AMD ?

IBM PS/1 Multimedia ( max restore ).

IBM PS/1 hardware service manual for jumper settings:
http://www.mediafire.com/file/u7lvbbx97i9xm9o … 3g2028.pdf/file

Intel486dx33 wrote:

But you need the overdrive CPU with 169 pins. It has an extra pin in the center edge of the CPU.
So look carefully for the Intel overdrive CPU with the extra pin.

If that's the problem, then be assured that the extra pin doesn't have any electrical function. All it does is to prevent user from installing the CPU in a wrong way 😀

It is actually better to look for CPUs without this as you can install them in 168pin sockets too...

Likewise you can install any compatible 168pin CPU to the 169pin socket as soon as you disable the original CPU somehow.

mpe wrote:

If that's the problem, then be assured that the extra pin doesn't have any electrical function. All it does is to prevent user f […]
Show full quote

Intel486dx33 wrote:

But you need the overdrive CPU with 169 pins. It has an extra pin in the center edge of the CPU.
So look carefully for the Intel overdrive CPU with the extra pin.

If that's the problem, then be assured that the extra pin doesn't have any electrical function. All it does is to prevent user from installing the CPU in a wrong way 😀

It is actually better to look for CPUs without this as you can install them in 168pin sockets too...

Likewise you can install any compatible 168pin CPU in the 169pin socket.

Yes, But the Intel Over drive CPU's have the built in 5v regulator.

No. They don't have regulators. Only the DX4 Overdrive (or Pentium Overdrive which goes to a different socket) does. And the DX4 Overdrive doesn't have the 169pin 😀

Other 486 overdrives are just re-packaged regular versions (OK sometimes with other minor insignificant changes to be absolutely precise). They are functionally identical.

You can clip the extra pin or install a normal DX2-66 and it will still work...

mpe wrote:

No. They don't have regulators. Only the DX4 Overdrive (or Pentium Overdrive which goes to a different socket) does. And the DX4 Overdrive doesn't have the 169pin 😀

Other 486 overdrives are just re-packaged regular versions (OK sometimes with other minor insignificant changes to be absolutely precise). They are functionally identical.

You can clip the extra pin or install a normal DX2-66 and it will still work...

Yeah, that's what I meant for the DX4

AlessandroB wrote:

I have discover that my PS/1 do not support CPU with 16kb L1 cache, 80486DX4 dos not work. Wich is the fastest CPU i can install? Even the POD require a specified compatibility System like 486DX4? tnks

Which model number PS/1 do you have ?
Because there are several models and the motherboards are different.

derSammler wrote:

It's not the size of the cache, actually. The problem is that all 486 CPUs with 16 kb L1 cache are using Write Back mode for it, unless you change it to WT in the BIOS (which you can't, since the BIOS does not know about it).

The original AMD DX4 (not the enhanced one) should work just fine when using a converter for 3.3V.

i am lucky, my AMD DX4 have 8kb WT

Intel486dx33 wrote:

AlessandroB wrote:

I have discover that my PS/1 do not support CPU with 16kb L1 cache, 80486DX4 dos not work. Wich is the fastest CPU i can install? Even the POD require a specified compatibility System like 486DX4? tnks

Which model number PS/1 do you have ?
Because there are several models and the motherboards are different.

Is not close to me, tomorrow i check. I have learned that IBM make several version of PS/1, why so confusion? Combination of cpu soldered, cpu socketed, minboard with overdrive socekt, 30 pin ram, 72 pin ram, if you do all the combination you obtain close to ten models... unbelivable... Mine is the version with DX33 on socket (not ziff.. WHYYYYYYYY!!!!) with 30pin ram and ET4000 VGA. not the best ma clote to be, the fastest one can be the one with orrible case.

There are two versions of DX4 overdrive. ODP and ODPR. The ODP version is designed to go into the overdrive/487 socket. It has 169 pins.

There are also VRMs which support overdrive pinout. With these you can take any 168 pin CPU and convert it to 169 pin format.

I'm not entirely sure what the deal with IBM is, but a lot of people report CPU incompatibility when trying to put upgrades in them. Maybe they did something funky with the BIOS. For example, 5x86 will only work in 3X mode, not 4X mode.

BTW, the fastest 486 CPU with 8kb cache, should be the AMDDX4-120, but your board probably doesn't support 40MHz.

AlessandroB wrote:

Intel486dx33 wrote:

AlessandroB wrote:

I have discover that my PS/1 do not support CPU with 16kb L1 cache, 80486DX4 dos not work. Wich is the fastest CPU i can install? Even the POD require a specified compatibility System like 486DX4? tnks

Which model number PS/1 do you have ?
Because there are several models and the motherboards are different.

Is not close to me, tomorrow i check. I have learned that IBM make several version of PS/1, why so confusion? Combination of cpu soldered, cpu socketed, minboard with overdrive socekt, 30 pin ram, 72 pin ram, if you do all the combination you obtain close to ten models... unbelivable... Mine is the version with DX33 on socket (not ziff.. WHYYYYYYYY!!!!) with 30pin ram and ET4000 VGA. not the best ma clote to be, the fastest one can be the one with orrible case.

Okay, so you have the base model PS/1. You need to set the jumpers for 33mhz and for an Intel 486dx-33 CPU.
then insert the Intel 486dx-33 Overdrive CPU into the overdrive socket.

The Intel Overdrive CPU oDP486DX-33-SZ802 Vintage Gold C3020228-B1. it reads 33 but it actually runs at 66mhz.

Download manual here:
http://www.mediafire.com/file/u7lvbbx97i9xm9o … 3g2028.pdf/file