PS/2 FAQ, Section 4

S) 4.0 Upgrading Processor/Coprocessor/Disks/Video/CDROM

Q) 4.1  I don't have the money for a new computer or motherboard, what can I do?

[PC Magazine 11-08-94, 

Kingston Technology makes upgrades to raise the level of all chips (i.e. 286 to 386, 386 to 486, 486 to 586).  Some are CPU replacements, others are daughterboard cards, and the granddaddy is the MCMaster.  The CPU replacements offer very little performance gain if your system is strapped with slow peripherals and memory, but can get you running 386 or 486 software.  The 
daughterboard 486/NOW! replaces both the CPU and math coprocessor, but performance-wise it is a disappointment.  The MCMaster is MCA architecture in action.  Using busmastering it allows the card to take over CPU functions and make the computer run a lot faster using its own 128k L2 cache and up to 32MB of memory.  This card shows promise and in most cases performs better than the daughterboards and CPU plug-ins, however it lags slightly in DOS video 
performance and video in general as it must 'cross' the bus on to the motherboard.  Still the MCMaster is probably the fastest in this list and the only upgrade that can add L2 cache to computers without the option.  [Formats:  486/NOW!:  models 70/80 to 33PD3 or 33PS3 (don't know what the PD3 or PS3 maybe D=DX and S=SX.); MCMaster:  for models 55, 56, 57, 65, 
70, and 80:  to 33 MHz or 50 MHz...note only 50 MHz with 8 MB+ boosted performance 
and so it did significantly.  The price for this level is $1000-1400.][NDP:  built in to the 486 chip.] 

Intel has a SnapIn 386 module for PS/2 models 50, 50Z and 60. It features a 20 MHz 80386SX, 16K cache and it can utilize an existing 80287 math coprocessor. I have one in a model 60 and have had no problems with it. 

IBM offers for the 386 PS/2 Model 70 and 80 with 16 or 20 MHz processors a Power Platform upgrade with a 486DX33 on it.  See above IBM PARTS LIST for features and part numbers.  These are expensive ($500-700) and are no longer made, but can still be obtained esp. from the Boulder Parts Surplus Plant 800-388-7080. 

IBM re-released the Blue Lightning chip for PS/2's again.  This time it is for the 25 MHz machines also.  It offers 16K internal cache, enhanced 386/486 instruction set, and 33/66 MHz performance (though the 33 will be replaced with whatever your system runs at).  Also you can add a math coprocessor.  The L1 cache design is supposed to be what sets this chip off from the rest (Hypertec).  I talked to a IBM tech who actually had the Cyrix DRx2-50 and was asked to help test out this new chip.  He stated he saw the same performance jump from going to a Cx486DRx2-50 from his 386DX25 as going to the BL2 from the Cyrix.  I would call that an upgrade worth considering, esp. at the mere $345 IBM is asking.  IBMPN#13H6698 $345. 

IBM also has a SLC2-66 chip out for 55SX offering up to 10x the performance.  Features 16K L1 cache, enhanced instruction set, and allows existing 387SX usage providing it is a 33 MHz chip. IBMPN#13H6694 $259. 

Cyrix offers very good options for the 386 to 486 conversion if you are on a tight budget.  Their DRx2 line offers clock doubled performance at a low price.  The chips perform very well and just require removal of the 386 and popping in the new chip.  Pricewise they can't be beat and though not offering the performance of their $500+ cousins they come close enough for most people at half the cost or more (This is due to their tiny 1k L.1 caches). [Formats:  386 to 486 only:  DX 16 MHz to 16/32 MHZ, DX 20 MHz to 20/40 MHz, 25 MHz to 25/50 MHz, DX 33 MHz to 33/66 MHz, none for 40 MHz yet.  DX 16 MHz and 20 MHz systems can use the 25 MHz chip if available.  Some versions for SX models.][NDP:  387,  Cyrix 83D87 rec.] 

Evergreen's Rev to DX4 and 486 chips are more expensive and generally faster than most others at a lower prices.  One problem is compatibility, many computers can not run at the clock tripled and quadrupled rates and must fall back to clock doubled rate negating the extra cost of the upgrade. Another note is the processor board cards will not work with all systems due to space constraints, it is best to measure and make sure you got at least 1" or more room above the processor and can afford to give up peripheral card space if it is in the way.  A processor card may be worth it if it works due to the fact of a larger L1 cache and the usage of an IBM Blue Lightning CPU in some formats.  [Formats:  386 to 486: DX 16/20 MHz to TI 486SXL2 or Blue Lightning 16/48 or 20/60, DX 25 MHz to TI 486SXL2 or Blue Lightning 25/75, 
DX 33 MHz to Blue Lightning 33/66 or 33/99; 486 to 486:  SX/DX 25 MHz to 25/75 MHz, 
SX/DX 33 MHz to 33/99 MHz, SX/DX 50 MHz to 50/100 MHz.  Note the DX4 only clock 
triples or doubles not quadruples like a DX4 seems it should.][NDP: various.] 

H.Co is offering many chips now from 286 to 486 all the way to a 386 to DX4/100.  I am interested to see how these perform as I have no info other than formats available.  [Formats:  286 to 486:  6-16 MHz to IBM 50 MHz; 386 to 486:  SX/DX 16/20 MHz to TI 40 MHz, DX 25 MHz to TI 50 MHz, DX 25 MHz to IBM 50 MHz, SX/DX 33 MHz to IBM 66 MHz, SX 16 MHz to IBM 48 MHz, SX 20 MHz to IBM 60 MHz, DX 16/20 MHz to IBM 60 MHz, DX 25 MHz to IBM 75 MHz, DX 33 to IBM 99 MHz; 486 to 486: 25 MHz to 75 MHz, 33 MHz to 100 MHz, 40 MHz to 100 MHz.][NDP: ?] 

A small company called MicroModules System also offers CPU upgrades.  They are at 10500-A Ridgeview Court, Cupertino, CA  95014-0736.  408-864-7437. Then there are AOX Inc.'s MicroMASTER busmaster boards. From 386-20 to  486/33 with up to 8MB of RAM on board. This is what the Kingston is now. Kingston bought the rights to manufacture the MicroMaster.  The early 286 to 386 versions can utilize 132PGA chips and usually 486DLC and DRx2 chips 
will work, but these are no longer made and must be found used or in surplus warehouses.  [Formats:  286 to 386:  to 20 MHz, 25 MHz, 33 MHz][NDP:  387.] 

In summary the MCMaster fully configured, i.e. 486/50 with 8 to 16MB of RAM offered the best performance, followed closely by Evergreen's DX4, Cyrix and finally Kingston.  H.Co, IBM, Intel, and AOX were not tested. 

Also note that adding 8MB of RAM will usually add as much performance as the CPU upgrades do and add a lot more performance if combined with the CPU upgrade.  The addition of RAM, a Video card, faster hard drive, and a new CPU will make the most improvement and if done over a period of time makes sense, however if these are going to be bought 'lump sum' it is probably better to buy a 486 clone if you are looking for speed.  If reliability is a big factor and speed not as important as being able to run the new 386+ software then with PS/2's usually there are no problems as there are with most clones. 

Update as of 10/28/98, there are no processor cards (AOX MicroMaster or MCMaster) available for the PS/2's anymore.  Evergreen and Kingston are still selling their processor upgrades and prices have fallen dramatically.  For the 486/33 systems you can get the AMD 586/133 (equivalent to a Pentium 75) for about $70 from CompUSA, Fry's, or Circuit City (list is about $129 for Evergreen's and $99 for Kingston). 

Q) 4.2  What are the Benchmarks for these Processor Upgrades?

Benchmarks are meaningless to give as it would not be the same machine nor the same variables but below are some 'averages'.  Benchmarks are only good to compare the same settings to the same settings so if you have a machine listed and have different marks don't post to USENET asking why, as it is simply because you have a different configuration.  The basic outline discussed above gives you the breakdown in percent a CPU upgrade is worth 36-134%, a daugtherboard is worth 137-681%(681% percent seems high and was not supported by PC Magazine's data. The 137% seems more real world as these are very close to direct CPU replacements for the most part), and an MCA processor card 263% which offered the largest increase, but at a very high 

Also note that a 486 is just an enhanced 386 with L1 cache.  This L1 cache is responsible for up to a 500% performance increase.  L2 caches can offer at most a 50% performance increase.  Try disabling all caching on a 33 MHz 486 and compare the marks to a 33 MHz 386 you will be surprised how close they are. 

Winstones are the most quoted benchmark today, so a table of average Winstones was computed.  Keep in mind that this benchmark is a benchmark which rates the execution of certain popular sequences, scripts, in about ten or so of the most popular window programs.  With this in mind this should give a *very* real world figure.  Also keep in mind that when the processor upgrades were done, the systems below remained stock which is very crippling especially with 
a 486 trying to pull files from a 20 ms access hard drive. 

The processor quoted benchmarks came from a database of at least 50 different platforms each for the 25, 33, 2/50, 2/66 with the 33 and 66 MHz numbers being taken as an average of no less than 50 machines for each.  This should give a good average number as there was no price range or brand criteria only what was available to the home user (i.e. no FCC class A or non-FCC tested dynamos). 

The 50 MHz numbers were for 5 tested machines.  The AM40, CxS40, and SLC2 numbers are for two or less machines each and may be bad examples of the capability of the chips being either superior or inferior to average numbers. The Pentium numbers came from an average by PC Magazine and should be a good average figure. 

Processor                       Winstone Value
386/25 MHz Winstone base w/4MB   10.20
386/25 MHz Winstone base w/8MB   13.60
486/25 MHz                       26.32
CxS40                           29.95*
486/33 MHz                       34.32
SLC2/50                         36.70*
SLC2/66                         37.80*
AMD40                           40.30*
486DX2/50 MHz                   43.50
486/50 MHz                       47.94
486DX2/66 MHz                    50.68
Pentium                         73.30
CX486DRx2/50                    14.20 --
Rev to 486 2/50                 15.40   \
Rev to 486 3/75                 18.00 
486/Now!                        11.20   / 
MCMaster 50PD/8                 15.00 -- 

Keep in mind these could vary a lotdepending what system the upgrade is going into (i.e. MCMaster was only tested on a 386SX16 machine and the rest a Compaq 386DX/25e with only 4MB and with 8MB the Rev to 486 2/50 did 23 Winstones and the 486/33 did 36.  So with more memory and better peripherals the upgrades should give truer 486 performance despite PC Magazines slams against them in general. 

Q) 4.3  Which Math Co-Processor should I use?

For 286 systems a 287, 386 systems a 387 and for processor upgrades usually the same unless they perform NDP functions on chip.  It may be wise to purchase an enhanced NDP, such as the 83D87 from Cyrix which is much faster (5-15% in applications, up to 20% on certain benchmarks) than the Intel part. 

Q) 4.4  Replacing a slow stock Hard Drive with a faster and larger capacity version

PS/2's are notorious for slow, low capacity hard drives.  The Model 50's 20MB drive has 80 ms access!  The easiest way to go is to add a SCSI or ESDI card.  SCSI in general offers better performance, the ability to add up to 7 peripherals and easy to find drives.  ESDI offers more UNIX compatibility (though with new drivers this will change) and was stock on some PS/2's, most now use SCSI.  If you have SCSI or ESDI already you can add at least one more drive no problem.  It is a bad idea in general to try and replace the MFM type ST-506 drives on early PS/2s as buying a SCSI card and new hard drive is a cheaper, faster and more reliable solution. 

Keep in mind that if you add a SCSI drive and controller make sure the controller has boot ability in the BIOS or else you will have to boot off of the original PS/2 drive. 

Q) 4.5  How can I add a second floppy drive and what type will work with my   PS/2?

Kits for mounting these drives can be obtained from PS Solutions 214-783-6997.  They sell high quality, complete kits for almost every possible internal drive mounting option. 

3.5" internal for: 
     25/30, 50Z/70, 50(front bay 50Z/70) 
     60/65/80         (via a 5.25" internal mount and allow for two half-high  3.5"/5.25" mounts) 

3.5" 'H'-skid type for: 
     35/40/56/57/76/77(via the 5.25" int. option) 

5.25" internal for: 
     35/40/56/57/76/77(all with 3.5" mount options available) 
     60/65/80         (vertical mount, also with dual half-high 3.5"/5.25"options) 
     90               (for removable media in the 5.25" bay w/ 3.5"HD opt.) 
     85/95            (for removable media and rails for fixed media) 

For systems with 'slide-it-right-in' options the necessary bezels can be obtained from DakTech 800-325-3238 very cheaply for a high quality product. (Also for bezels with missing clear plastic 'windows' which make it hard to see the drive lights.) 

First, we will discuss the 3.5" addition as it is a more common event. 

The first thing you need to do is to determine the MB capacity of what you want to add.  There is 720K/1.44MB/2.88MB and they can all read/write at their level or lower (i.e. a 2.88MB can read/write 1.44MB and 720K).  Not all systems can use all 3.5" drives.  [I would like to include a list of which systems CAN'T use the 1.44MB drives and which systems CAN use the 2.88MB 
drive].  After determining what you need/want to add you can start the installation. 




There are two types of 1.44MB drives and though they do the same thing they are not interchangeable on the internal level.  One has the disk light above the media slot and the other has it below the media slot (there are other ways  to tell but this is the easiest method).  Once you determine this it is simply a matter of either popping off the faceplate bezel blank sliding in the disk 
drive until it 'clicks' and popping on the new bezel.  Sometimes the external case needs to be opened like a model 50 for example, but then the procedure is the same. 




Now we will discuss the addition of a 1.2MB 5.25" drive. 

These can be both adding internally or externally.  External is the common way as most PS/2s do not provide a 5.25" floppy bay and those that do usually require a vertical mounting arrangement. 

*The models supporting a direct 5.25" mount internally are: 

All other's need to either buy the kits listed above or need to use an external mounting option. 

*The internal 5.25" drive is installed by sliding it into the bay  [someone please contact me with the directions for the direct installs they click into place like the 3.5" drives or do they require 
screws/or combination.] 

The kit-type installations are completed by following the manufacturers guidelines for the kit then going to the drive hookup section below. 

*Hooking up the drive to the drive card: 


Find a place on you desk or area where the likelihood of the drive being knocked down is low.  Then set the drive down and detach the cable if possible from the drive to prevent it being dragged around in the installation procedures. 

Now you are ready to set it up: 

Open the case of the computer, find an empty MCA slot. Plug in the floppy controller card and run the cable to it.  Now close up the computer and plug in the 5.25" external drive and you should be all set. 

Cristie drive (available only in the UK?): 
The drive connects to the B-3.5" floppy connector. The cable then goes inside the computer, through the slot in the back and finally to the drive. It doesn't actually use a slot, but looks neater than having a cable run out the front B: drive bay to the 5.25" drive. 

Radio Shack/Tandy's 5.25": 
This drive will give you 360 and 1.2mb formats via the parallel port, and allows you to plug your printer in too -- so you lose neither a drive bay, an expansion slot, or much money. The drive can be temperamental, usually requiring a print job before the drive is acknowledged (maybe initialization of the parallel port is what is required). The print job can be empty also. This drive is an ideal solution which lets you keep your tape backup and expansion cards in place, even if requiring an extra step to use the drive. 

Sysgen unit: 
Its not a very awkward installation.  Just pop off the cover. Unplug the floppy connector.   Snap a small board in on supplied post, and re-install the floppy connector and route the other out the box to the external unit. It works as drive B in 1.2 meg mode.  The IBM's I saw mapped above the last hard drive, so that floppy came in as D or E. Works fine with SCO Xenix too. 

[I have been informed that the IBM drives also require the usage of one of the 3.5" floppy bays for a second drive card, is this the case for all 5 1/4" drives?] 

Q) 4.5a  What is the Third floppy connector for?

That is for a floppy controller based Tape Drive (The ITBU comes to mind). If you want to be retro, go for it, but any decent SCSI based tape will clean the floor with a floppy controller tape. 

I did run three floppy drives in a 90 once. W95 did not like it (MS-DOS mode) but I was able to access all three floppy drives. 

Q) 4.5b  Will the * floppy drives damage my floppy controller?

They are Mitsubishi MF356F-899MF 2.88MB floppy drives. They have the "*" on the top of the blue eject button. Do NOT use * floppy drives in a 9585 (all models), Lacuna based 76 / 77 systems, and in 95A (dual serial / parallel ports) planars.   At this time, Peter Wendt opines that the extra wires used by the security features on the listed systems are not properly handled. 

At present, I am confused. I pulled * floppy drives out of Bermudas with a 44 pin floppy controller header. There does not seem to be a specific floppy controller related to the problem, as the Bermudas had 82077AA, 82077SL, or NS PC8477AV with * floppy drives attached. 

Q) 4.6  Is there a SVGA option for my PS/2?

There's XGA and XGA/2 from IBM and the Reply Video Adapter from Reply Technologies. Both of these have 1MB of unexpandable VRAM and can display 256 colors at 1024x768 non-interlaced and go to 1280x1024x16.  The IBM card uses a IBM chip and the Reply the Cirrus Logic CD-GL 5426 chipset which is VESA compatible. 

IBM also has a SVGA card for servers.  As such, it maxes out at 256 colors. 

A note about XGA/2, it is not VESA compatible at the hardware level...there are drivers that allow it to be VESA compliant but these drivers freak out many pieces of commercial advised. 

Also on the high end, I know of Matrox making some in the $1k + range that have 1MB+ of VRAM but I have yet to hear of the performance or to run into someone who has purchased one.  Also RasterOps Colorboard 1024MC can display 1024x768x16.7M (no modes above 1024x768) with the 3MB of VRAM it has, but it is slow compared to other video cards and expensive. Also I am curious as to the specs of the IBM Image I Adapter which is about $2.7k with 3MB VRAM for 1280x1024x256 color support. 

ATI has the Ultra Pro 2MB a 2MB VRAM card with a 32 bit accelerator.  This card had be found for as low as $250 (retails for ~$500)[prices as of 1996].   I am curious to its performance as the 64 bit versions are top in their class, but for just the ability to get greater color depth the 2MB card is worth it.  Be advised that ATI has the habit of constantly changing its drivers so compatibility issues may arise and a downtime for new drivers may be upon you.  It uses the Mach32 chipset so is widely supported, NT 4.0 supports this also. 

Q) 4.7  How can I add a CD-ROM drive to my PS/2?

Most of the time an external CD-ROM can be added if you have a SCSI card with no problem.  Internal CD-ROMs can be added to any PS/2 with a 5 1/4" bay, some that have internal 5 1/4" bays (60/65SX/80) can use special bezels to vertically mount a CD-ROM.  In these cases caddy-type drive are mandatory. The drivers needed are usually dependant on which SCSI card you use so contact the manufacturer if CD drivers were not supplied. 

Use the cheap AT Drive rails for 85 or 95 installations. You have to shorten the rails a bit on both ends. You don't need a CD-ROM bezel for these, as it's a close fit. The drive will be retained up front by the drive retainer. If you want a professional look, then get the bezel. 

For 56, 57, 76, or 77 installations, the CD-ROM bezel keeps the CD from sliding out of the case (tis true!) 

Q) 4.7a  Jumper Settings for a CD-ROM

   Usually, the CD-ROM is jumpered as ID 0, that is NO jumpers on any "IDx" pin. It's a relatively slow device on the SCSI chain. IF you have a multimedia system, you may want to set the CD to ID3. You MUST have "Parity" jumpered. IBM SCSI devices require parity (some Apple CD-ROMs do not have parity, and cannot be used). 
  Leave PRV/ALW alone. If you cannot eject a CD, check this jumper. Leave "Test" unjumpered. If the CD is the last device on the SCSI cable, jumper "Term". This assumes that you have the terminating resistors (SIPs) or the termination is built-in. If it's an older model that uses discrete terminators, and they're lost, either get an in-line terminator or put the CD in the middle of the SCSI cable where it doesn't need termination.

Q) 4.7b Installing DOS/W9x on a CD-ROM w/IBM SCSI Controller

   You need the IBM CD-ROM driver and ASPI4B.sys to do this. Two places to get info are HERE which has Dos and W95 autoexec.bat and config.sys examples, and HERE which has the more involved method. 

  Do you need IBMCDROM.SYS and ASPI4B.SYS? This way you can get the device drivers and edit the autoexec and config yourself without finding or creating a 720KB floppy... 

Q) 4.8  How can I build a Multimedia PS/2?

You can build a multimedia PS/2 the same way as a normal PC.  The exceptions are sound cards.  As it stands now you must use the SB-pro or clone for DOS and the Audiovation/A or equivalent for windows.  Any SCSI CD-ROM should work with a SCSI card and any big monitor will work.  Reply Technologies, Matrox, and ATI all make video cards for SVGA, some have up to 3MB of RAM. Also any speaker setup will work with the soundcards providing they have they same connectors (usu. RCA or mini RCA).  Other than that you will want a fast hard drive and probably a 33 MHz or faster machine. 

Here is an example: 

PS/2 Model 80-A21 
Cyrix Cx486DRx2-50 Processor upgrade with 33D87 NDP. 
Mag DX15F Monitor 
Reply Technology Video Adapter 
Plextor 4x CD-ROM (internal mounted) 
Piper or ChipChat SB-Pro sound card 
Audiovation/A sound card 
Seagate ST-3600N SCSI hard drive 
Future Domain MCS-600 SCSI controller. 
Sony Speakers 
CH Game Card III 
Generic PC joystick 

Q) 4.9  How can I get sound effects in DOOM?

[From: (Cousin AD)] 

Option #1: 
Choose all the WRONG settings for the DMA, IRQ and I/O address.  Save settings and play...  You may still need to re-boot one time before this works. 

Option #2: 
Choose the wrong setting for the I/O Address (use the correct settings for the IRQ & DMA). 

The above worked for me, but I found problems setting-up for modem play...  I figured, hey, you can't have it all...  Then I got another suggestion that really solved the problem... 

Option #3: 
Choose all the CORRECT settings for the DMA, IRQ and I/O Address.  Exit set-up and choose yes to "Save settings before exit."  Then, before starting DOOM, open the file DEFAULT.CFG in an ASCII text editor (MS-DOS "EDIT" for instance).  Change the "SND_SBPORT" line from 544 to 220 or 240, depending on your SoundBlaster MCV configuration.  Save the DEFAULT.CFG file and start DOOM... 

Q) 4.10  How can I make my PS/2 Model 90/95 a Pentium 180/200MMX machine?

Warning! I have seen reports of complex failure and death resulting from this mod or similar ones. The cause is the upgrade CPU is trying to suck enough power from the Voltage Regulator. Problem is, the traces or VR don't have the extra oomph needed. I had a Terminauter interposer complex start to go flakey after six or so months.
   A possible solution is a Madex interposer. It has the external power tap so it can drive the cpu from the power supply.

First it is going to always be a P180MMX as the clock tripling runs at 3x60 and there is no easy way to modify this, although if a budding Electrical Engineering student wants to do so I am sure the list would love a P233MMX version. 

Secondly, you must use the Overdrive version of the P180MMX or P200MMX as the non-Overdrive version do not work properly in this capacity. 

Also note the P90 version of the Type 4 complex is needed.  Contrary to popular belief all of the Type 4 complexes are as different from each other as they are to the Type 1, 2, and 3 complexes (as well as each different kind of those). You need the "Y" upgrade of the Type 4 complex, announced Oct 1994, and known as IBM Part Number/FRU#  06H3739 or 19H1027 (and a few other crossreferenced numbers). 

The "P" and "Q" complexes use a 497 cache controller, which is unfortunately incompatible with Overdrive CPUs. Some experiments have been made with varying success. 

These go for about as much as a small third world country (or half the continental United States if purchased directly from IBM).  So make sure you can afford to lose this board should any of the below modifications screw up your processor board or PC.  If performed as outlined and no mistakes are made it is a totally reliable modification and brings your machine to the front of the pack.  Remember most applications peak out at 200-233 MHz Pentium speeds and the PII's are really only useful for games, high-end graphics, and high-end multiuser server applications. 

The complete breakdown with pics is available HERE.


Modifying your processor complex with these instructions will void any remaining warranty and may cause irreparable damage resulting in a non-functioning processor complex if performed incorrectly. There are no warranties expressed or implied. Modify at your own risk. (Manufacturers warranty on newly purchased PC Server 500's was usually three years depending on country of purchase. Check your warranty information if concerned or unsure. Optional service contracts may have altered or extended your period.) 


The following instructions can assist you in modifying the 90 MHz Pentium processor complex that was originally manufactured in the IBM PC Server 500 System390 so that you can use the Pentium® Overdrive 180 MHz with MMX chip. If you unplug the Pentium® 90 MHz chip from the complex and plug in the 180 MHz Pentium® Overdrive without this modification, you will experience two problems: 

I. The electric fan that cools the Pentium® Overdrive chip will not have power to turn the blades. You will 'cook" (burn out) the Pentium® Overdrive due to inadequate cooling. (The 90 MHz Pentium® chip uses a heat sink instead of an electric fan.) 
2. Without providing 5 volts to the overdrive chip, the chip will run at about 25 MHz which is slower than the installed 90 MHz chip. 


* Locate and have a working reference diskette for the PC Server 500 available. 
  You will need it if you use a different processor complex board than the one currently installed. You should not need it if you remove, modify, and replace the same processor complex board that is currently installed. Better to locate and have it ready than to not have it. 
* The processor complex does not use a ZIF (zero insertion force) socket for the Pentium® processor. The old 90 MHz processor must be carefully removed. (A good quality jewler's screwdriver was useful to the author in starting to pry the chip from the socket and then working around the perimeter of the chip increasing in small increments. Insert the tip of the screwdriver between the socket and the chip. Use only the socket surface and not other chips or edges on the board as fulcrums for prying.) 
* Solder an insulated wire from the +5 volt regulator to the two unused pins on the Pentium® 'internally no-connect'. 
* The two pins are technically labeled AN01 and AN03. There are no labels visible that say AN01 or AN03. 
* After the wire has been soldered to all three points and allowed to cool,   carefully align all pins of the new processor to their respective holes taking note of the key (missing pin on one corner). Carefully push the new processor into the holes. The new processor pins may be longer than those of the old processor and therefore there may be a gap between the bottom of the new processor and the socket surface. 
* Reinsert the processor complex into the PC Server and reconnect the signal wire. 
  Power on the server and assure that the fan on the Pentium Overdrive processor is turning (a flashlight aimed at the fan when power is applied will probably be necessary). 
* You will note that the LED display on the front of the PC Server 500 will say "60 MHz" instead of "90 MHz." This is normal. 

Modify at your own risk! Modification will void warranty.

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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