This is a note to Aptiva 2168-Mxx owners that there have been several successful upgrades of M41's to run an Intel P166MMX cpu. This is not an OD, but a regular P166MMX. The M53 motherboard is identical to M41 and so this upgrade can also be done. By way of comparison, a 166MMX is a more powerful (and much cheaper) cpu than is a regular P200 cpu.

This table lists Intel's published performance metrics according to the iCOMP system.

For those of you who want a P166MMX cpu, here are your options.

1) Buy an overdrive cpu. If you do this, it would be best to increase your bus speed to 66.6MHz by changing JP2 and then buying the overdrive for a 100MHz Aptiva (like an M53 model).

2) Do not buy an overdrive cpu. Buy a VRM (voltage regulator module) from IBM for $25. For Canadians, call the IBM-Direct depot in Toronto at 1-800-263-2769 and ask for part 76H3658. This is actually a Semtech VRM part MP55C-3.3-2.8. IBM also includes next-day Purolator delivery in the $25. It has also been found that the Semtech VRM part MP55C-5-2.8 also works. You cannot install any MMX cpu without a VRM.

Also buy an Intel 166MMX. Canadian web site www.megadepot.com was selling the Intel box set for a decent price. The AMD and Cyrix cpu's are cheaper, but to my knowledge they will not work in these Aptivas. You will also need a heat sink and fan. There are two options for buying the cpu. One route is to buy just the cpu and buy a separate heat sink/fan. That normally does not have much if any warranty. The other is to buy the Intel box set. The Intel set has a fan, heat sink, a 3-year warranty, and assurance that it is a real 166 instead of a remarked 166. The box set typically costs very little extra. Many places charge the same as for the cpu by itself. It is also suggested you get some thermal compound to seal the new cpu to the heat sink. You will not need the large size tube of compound!

It might be worth considering if or when you want to upgrade. IBM currently has the VRM piece in stock. The VRM is needed to convert a classic Pentium PC to an MMX. VRM demand likely stops when those upgrades stop.

The upgrade procedure for the VRM/166MMX is quite simple. If you have installed a second hard drive or CDROM, you may want to remove it to get better access to the VRM socket. The step-by-step procedure is as follows.

1) Check the BIOS version. This is done at startup by pressing F1 during the boot-up. BIOS version BGOUS1K is known to work, which is the latest available for free from the IBM web site. Any BIOS upgrade must be done prior to continuing. The minimum BIOS on which to try this is probably BGOUS1H or BGOUS1J, although that is untested. The original M41 BIOS definitely should not be used.

2) Power down the PC and disconnect all wires from it, including the power cord.

3) Work on a good surface. Using an anti-static strap at all times is recommended. Working on your knees on the carpet is not recommended. You will have to lay the mini-tower PC on its side. I don't know the layout of the desktop models. The mini tower casing comes off by removing the two bolts under the handle. Pull the casing forward and it slides off.

4) Remove the shorting block from the VRM socket. This is J19. It is immediately above the cpu. The cpu is on the right underneath a big black heat sink. There are two plastic clips that have to be pushed back to release the shorting block. The clips may be covered with tape. The tape does not need to be replaced. J19 is a 30 pin socket (two rows of 15 pins). Check your VRM for its size. DO NOT power the MMX cpu with the shorting block in J19 unless you want to destroy the MMX chip.

5) Install the VRM in J19. Be certain to close the socket clips that hold the VRM in place.

6) Change the following jumpers settings.

a) Jumper JP2 sets the I/O bus speed. It must be set to 66.6MHz (which is maximum). This is done by jumpering pins 3-5 and 4-6 together. The correct settings appear as:
2 4-6
1 3-5

b) Jumper JP21 sets the clock amplitude. It is currently set to connect pins 1-2 for a 5v clock. This must be changed to select 3.3v for the MMX cpu. This is MANDATORY. Change JP21 to connect pins 2-3.
DO NOT power the MMX cpu if this jumper is not correctly set unless you want to destroy the MMX chip.

c) Jumper JP3 sets one of the clock multiplier inputs to the cpu. It must be set to connect pins 2-4. Note that the motherboard indicates that JP3 pins 3-5 must be jumped for P55C, which is MMX. That is INCORRECT. Leave JP3 jumpered as 1-3. The MMX will not boot if you change JP3 to connect pins 3-5. The correct setting appear as:
2-4 6
1-3 5

d) Jumper JP25 sets one of the clock multiplier inputs to the cpu. It must be set to connect pins 2-3.

6) Remove the heat sink on the P75 cpu. This requires unlatching the silver clip that holds it in place.

7) Open the ZIF socket for the cpu. This is done by opening the lever attached to the top of the cpu socket. The lever is hinged on the left of the cpu socket. There is a little catch that holds the lever in the closed position.

8) Remove the P75 cpu. It will come out with no force at all. Just pick it up. It should be safely kept in an anti-static bag or anti-static foam in case you need it later.

9) It is suggested that you record the markings on the new cpu prior to installing it, or on your old cpu if you re-install that.

10) Check the new cpu for bent pins. If there are no bent pins, insert the new cpu. Be certain that it is correctly oriented in the socket or it will get destroyed when powered up. The cpu will have one corner flattened or marked. Line that up with the socket corner that is flattened or marked. As I recall, the board diagram from the IBM homepage shows the socket incorectly in terms of locating the flattened corner. Go by what is installed in the board!

11) Make sure the cpu is fully down into the socket and then close the ZIF socket by closing the lever and locking the lever in place. The cpu must be all the way down into the socket because the heat sink is going to press down onto the cpu.

12) Put a SMALL amount of thermal compound on the top of the cpu. It does not take allot! This is a really thin coating to compensate for any imperfections in the contact between cpu and heat sink. You do not want excessive compound squeezing out the sides. It does not even need to cover the entire top of the cpu. Just a square inch in the middle is enough. Remember that the heat sink is going to be very tightly pressed onto the cpu. Use what you found on the P75 cpu as an example.

13) Verify that the cpu is oriented correctly in the socket, and then place the heat sink/fan combination on top of the cpu. The heat sink should have a bar that fits into a slot beside the cpu (expected to be on the left of the cpu, if I recall correctly). The heat sink MUST be fully flush with the top of the cpu. A poorly fitting heat sink is better off replaced.

14) Lock the heat sink in place using the silver clip in the same latches as when it was removed.

15) Plug in the fan. There are two options, depending on your fan. If it has a miniature plug, then there is an open miniature 12v socket near the cpu. If it has a large plug, then use one of the PC's main 12v plugs. In this case, the fan will have a Y-adapter and so provide another available 12v plug for the one it used.

16) Check the work for correct installation of the VRM, cpu and correct jumper settings.

17) Reconnect the PC wires and power.

18) You can start the PC. The BIOS will detect a P166 cpu because it is not written to recognize MMX. You still have all the advantages of MMX.