486 Interposers and Upgrades

Pin Assignment

AMD 5x86 133 - The whole story (by Jan Steunebrink)

General Information
   EverGreen 586 (4x)
   EverGreen 586 Am5x86 QFP (4x)
   PowerLeap PL586 (4x)
   PowerLeap PL586-133 QFP (4x)
   JC World Am5x86 QFP (4x)
   Buffalo HAS-33T (3x) (Melco?)
   ACE 486 (3x)
   Unknown PGA DX4/2 Interposer (4x) (JC World?)
Upgrade Kits
   PowerStacker 5x86

Content created by Sandy. Edited by Major Tom.


General Information

486 CPUs in SX/DX/DX2 line made by Intel work in 5V I/O voltage. Intel DX4 and other High Power CPUs sold by Cyrix and AMD work in 3.3V to 3.45V I/O voltage.
In order to use such CPUs on PS/2 or PS/55, you need to use an interposer which switches down planar 5V to required voltage for those CPUs.
If you put a plain DX4-100 in your Bermuda or K/H complexes, your CPU will get toasted in someday (not immediately but slowly. I myself didn't imagine that DX4-100 would work with 5V supplied but it could work actually. Not tested with Cyrix or AMD though).

These interposers usually have jumper blocks for:

  • Multiplier selection
  • WT/WB selection
  • I/O voltage selection
  • socket type selection
  • Intel/AMD selection

Appropriate setting of an interposer for each CPU is needed to get full potentiality of these high powered CPUs.

But so far, your CPUs will not get toasted with *wrong* jumper setting unless you put your CPU onto the interposer with wrong orientation of pin #1 (as far as I know, 486/586 CPU will not get toasted with it. 386 and Pentium will immediately go to heaven) or you erroneously set CPU off on "one-row" beside correct position (this will also send your CPU to heaven at once). Of course I'd like to advice you DO not test such stupid trial, OK?

According to old PC magazines sold in 486DX100 era, there were compatibility issue for interposers and DX4 and /or AMD/Cyrix. An interposer worked OK with DX4-100 on a system A but not good on system B. The other was OK on B but not on A.
One of PC upgrade shops sold various versions of AMD upgrade interposers which were arranged to work with specific model-types. I got one from the shop for my 5551-NAB and it was designated as "tested on ....PS/55 5551-NXB....". There was another model designated for IBM PC Master 100 and such. These kits were cosmetically all same.
The shop did some trick or magic to their products. Because I didn't know much about IBM products and model numbers of PS/55s, I really worried if the kit for NXB might suitable for my NAB or not.

Now I really feel strange that all of my interposers I had bought very cheep or got free in as-is condition or as "junk" not knowing about their specification worked fine on my PS/55s.

By the way, in Japan we commonly call interposers "GETA". GETA are Japanese wooden sandals. :)

EverGreen 586

Sold by Evergreen together with Cyrix5x86 100/4x, 133/4x.

ET9603.EXE Evergreen's Cache enabler ET586 for Cyrix 5x86 and other related programs (including ETDIAG.EXE). Also contains cache enabler for DOS, OS/2 Warp, and NT.
Execute the file with -d (or /d) option to create a complete install diskette with sub directories.

5x86REGE.ZIP Spreadsheet of hex values for ET586 (Nifty ID: F355)

5x86reg.lzh The original spreadsheet written in Japanese (Nifty ID: F355)

5x86c2.ZIP Cache Enabler for Cyrix 5x86. Contains cache enabler for DOS, OS/2 Warp. (Peter Moss).


4x/3x/2x selectable, WT/CB (Cache Back?) selectable, Will fit both on OD/Main socket.

Top View Bottom View Cyrix 5x86-100/4x w/ EG Fan

Jumper Settings

3 pin block beside DC connector for a fan: Clock multiplier
      Set jumper as designated on the PCB
3 pin block in the middle position: Cache back setting.
      CB for W/B cache and W/T for Write-through
3 pin block at the corner (opposite to pin #1): Socket type select
      OD for Overdrive socket and the other for standard ZIF or main socket.

EverGreen 586 Am5x86 QFP

Am5x86-133 QFP package is soldered on the PCB.

4x/3x speed selectable, WB/WT selectable, socket position selectable for Normal/Overdrive.

Top View Bottom View

Jumper Settings

Left: Socket type select
      OD for Overdrive socket and the other for standard ZIF or main socket.
Center: Clock multiplier
      left-center for 3x, center -right for 4x
Right: L1 Cache status
      left-center for WT, center -right for WB

PowerLeap PL586


4x/3x/2x selectable,  WB/WT selectable, Will fit both on OD/Main socket.

Top View Bottom View Am5x86 w/ PL heatsink/fan

Switch Setting

DC connector for fan assy is placed on the surface of the PCB.
Micro Switch block is placed in the middle of pin side.

SW1: Socket Type SW2: Cache Mode [1] SW3: Clock Multiplier
On (Up) Standard/486 Write-Back 2x, 4x [2]
Off (Down) OverDrive or 487SX Write-Through 3x

[1] - SW2 is ignored for a TI486DX4 and Cyrix 5x876 CPU. WB/WT function selection for the TI486DX4 and Cyrix 5x86 CPU is auto-detected by a system BIOS. If your system board doesn't support the WB function, the system BIOS will automatically set the CPU to to run in WT mode.

[2] - Clock-quadrupled for AMD-5x86-133 and Cyrix6x86-133 or higher. Clock-doubled for Intel/AMD/ST 486DX4-100 and Cyrix5x86-100 or lower.

PowerLeap PL586-133 QFP (manual)

Clock-tripled/quadrupled processor upgrade for 486 systems. A QFP version of the AMD Am5x86-P75 CPU is permanently soldered on the interposer.

JC World Am5x86 QFP

This one is supposed to be a modified version of PL586. There aren't any jumpers for speed selection - it's fixed to 4x operation.

Top View
A special ROM (huh? PLA maybe?) is mounted inside the socket plug. JC world made several versions for their products so that their interposers could be used on various systems. Due to presence of this component, this Overdrive kit doesn't fit in some systems. For example, the ZIF socket in 5551-N or LIF socket on Type-4 N won't accept this interposer.

Buffalo HAS-33T

I'm not sure about this interposer. It's branded as "Buffalo"; known to you as Melco.
Designed to be used on ODP socket with a key pin (169 pin PGA layout. see picture below in the middle).
I think this one is mainly used for NEC PC98 series PCs. I don't know how the jumper block works. But so far, it works on my PS/55s.
Basically this is 3x capable interposer but there is unused register block connected to R17 at the bottom side. It should be possible to remake it to 4x(2x) capable interposer.

A photo of the packaging and accessories can be found HERE.

Top View Bottom View Cyrix 5x86-120GP w/ fan

Jumper Block Probing

If my observation is correct, jumper Blocks JP3 & JP4 should be set in combination of 1-2/1-2 and 2-3/2-3.
This interposer has no Voltage Selection jumpers nor Speed Selection jumper.
Probably this was designed to use an Intel DX4-100 and other 5x86 CPUs for:

  • system which has only one (MAIN) socket (doesn't matter if it is a 169-pin socket or 168-pin socket)
  • system which has a soldered QFP SX CPU with an ODP
JP4 Pin 1 N/C
Pin 2 Connected to B14 at PIN side
Pin 3 Connected to Vss
B14 : UP# (OUT) for OverDrive CPU (ODP)
UP# (IN) for SX QFP & DX/DX2/DX4

JP3 Pin 1 Connected to C14 at PIN side
Pin 2 Connected to C14 at CPU side
Pin 3 Connected to A13 at PIN side
C14 : FERR# for DX/DX2/DX4
A13 : FERR# for ODP

Jumper Settings (my presumption)

CPU JP3 JP4 CPU Type & Socket Type
CxDX4, 5x86
Pins 1-2 closed Pins 1-2 closed Main without SX CPU
Pins 2-3 closed Pins 2-3 closed ODP Socket with a QFP SX

ACE 486

This one is very simple. Really wondered if it could handle 5x86 CPUs but it does.
Basically this is 3x capable unit. But it is easy to remake it 4x operation with a simple soldering rework.

Top View Bottom View Am5x86 w/ heatsink/fan

Green rework wire observed in the pics is not for 4x speed. It's for ODPR CPU to be set in ODP socket. B14 (UP#) was connected to Vss. Then A13 should be connected to C14 but I left it undone (I noticed most of PS/55 ODP socket can take ODPR thus the rework was not completed).

4x rework can be observed in middle pic. R17 connection to Vcc was disconnected and rewired to Vss. (usually R17 is left open for 3x operation and is internally pulled up within CPU). Enlarged picture HERE.

Unknown PGA DX4/2 Interposer

Don't know correct name of this product. I think this one was contained in a CPU upgrade kit sold by JC world, one of famous PC upgrade shop back in '97, but not so sure.
There were similar kind of interposers which looked like very close to each other back in those days. I got mine to upgrade my 5551-NAB and I am not sure if this is the one or not.


4x/3x/2x capable, Intel/AMD( dx4) selectable, 3.3/3.45 selectable. No jumper block for WB/WT

Top View Bottom View Am5x86 w/ heatsink/fan

Jumper Settings

J1: Multiplier for Intel CPU (but including AMD 5x86 and Cyrix5x86)
      1-2 for 2x and 4x, 2-3 for 2.5X, open for 3x
J2: Multiplier for AMD DX4-80/100
      1-2 for 2x, off ...dunno have no AMD486-120
J3: Voltage select
      1-2 for 3.45V, 2-3 for 3.30V

Upgrade Kits

PowerStacker 5x86

Information about the PowerStacker 5x86 Upgrade HERE.

Content created and/or collected by:
Louis F. Ohland, Peter H. Wendt, David L. Beem, William R. Walsh, Tatsuo Sunagawa, Tomáš Slavotínek, Jim Shorney, Tim N. Clarke, Kevin Bowling, and many others.

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