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Introduction
Model 8525 (8086) Upgrades
Model 8525-286 Upgrades
Model 8525 SX Upgrades
Model 25SX Upgrades
A Word About Upgrade Planars
Based on content by William R. Walsh (original HERE). Edited by Major Tom.
Introduction
The three different models of the Model 25 all have very different upgrade
options.
The only upgrades common to all Model 25 models (except the 25SX, which has
no replacement planar upgrade) are the 7386 or the use of a Reply board. Reply
board information is here, and the 7386
information is here.
Model 25 (8086) Upgrades
This model in the Model 25 line is the least upgradeable of all three
models.
The only CPU upgrade you can get is to use an NEC V30 CPU in place of the
stock 8086. This gives a slight speed boost, but will not enable your system to
use software that requires the protected mode of the CPU as found in 286 and
higher systems. Boards that upgraded XT systems to become 286 or 386 computers
do exist, but I have only seen units made for use with the 8088 CPU, not the
8086 as used in the 25XT.
A Reply PowerBoard, PC Enterprises Genesis\PC or IBM EduQuest 7386 is
really the only upgrade for this system that will bring you to a fairly modern
CPU with more expansion options in terms of performance and software
selection.
Most systems come with the maximum of 640 kilobytes of RAM. Although
expansion of the RAM through use of an EMS RAM card is possible, most software
that uses EMS RAM requires a 286 or higher processor.
The hard disk may also be upgraded with an aftermarket controller and drive.
You will have to remove the hard disk already installed in the system if you
have one. Such aftermarket controllers have their own ROM BIOS to boot from, as
the system itself does not have support for standard drives. This is probably
the best and easiest method with which to install a hard disk. The new drive
will be faster, quieter, more efficient and certainly more reliable than the
original.
Both IDE and SCSI controllers with their own BIOSes exist and can usually be
found used at a very reasonable cost. You need a controller that works with an
8 bit ISA bus slot.
Model 25-286 Upgrades
The Model 25-286 can be upgraded to have a 486-class CPU at best.
The most common upgrade available is a Kingston SX Now! upgrade. These upgrades
make your 25-286 into a 386SX system, at either 20, 25, or 33 MHz. You will
need SX Now! upgrade model SX/xxLEM. Other models won't fit — this model
is designed for the Model 25-286. The "xx" in the model number will be the
upgrade's speed.
Other upgrades exist, including some that offer up to 486 processor levels.
Speed on any of these upgrades is not going to be as good as having a "real"
386 or 486 based computer. Basically, these upgrades are "super 286" chips that
run really fast, and they can run 386 or 486 instructions, thus allowing you to
use software that would require a 386 or 486 processor. A lot of these upgrades
also have a lot of cache on-board to speed operation even further. You will
need a program to turn the cache on for most upgrades — or the upgrade
will run at just about the same speed the original processor did. You can find
the program for your particular CPU upgrade from whomever the
manufacturer/vendor was.
You may also use a Reply board or the 7386 planar upgrade in this system.
The Reply and IBM 7386 upgrades give you the most performance, with vastly
improved RAM expansion options and a choice to use a larger/faster hard disk
without the use of a separate controller card taking up one of the two valuable
slots.
The memory in this computer can be upgraded to a maximum of 4MB on the
planar board. Using an adapter card, you can achieve 16MB of RAM, but the
adapter card must support changing its starting address so it won't conflict
with the first 4MB of RAM. Unfortunately, RAM for this system doesn't come
easily. IBM used chips with a different CAS/RAS refresh system and they also
set up the parity differently. And while common 30 pin SIMMs can be hacked for
use with an IBM SCSI adapter (which uses a similar system to the 25-286 for
memory) they have proven to be less than reliable or totally unusable on the
25-286. However, some folks have reported that this may be a problem solved by
using 9-chip 30-pin SIMMs instead of 3 chip ones.
Your options for a hard disk are the same as the 25-XT model above.
Model 25SX Upgrades
The Model 25SX can be upgraded to have a 486 class CPU at best. But not all
systems can be upgraded. The very first Intel 386SX 16MHz processors don't have
the ability to be disabled by grounding a certain pin the CPU itself.
Fortunately, it seems that the vast majority of 25SX systems use a 20MHz 386SX
processor — and all of those DO have the needed pin to be turned off when
an upgrade is installed.
The only advice I can offer on whether or not your Model 25 is one that can
upgraded is to look inside in the system or check the CPU's stepping number.
When looking inside the system at the CPU, you will see 1 of 3 possible things
printed on the chip. The first will be a simple "80386SX-16". Most CPUs bearing
this mark are not upgradeable. The second you could see is a chip marked as 16
or 20MHz with the additional printing "C Step". These processors support
installation of an upgrade CPU. The third and final variation you may see is a
processor that says "80386SX-20". All of these processors can handle
installation of an upgrade CPU.
If you don't want to open your 25, software exists that can tell you your
CPU's stepping number. This number is sort of like version numbers as used in
software programs. Do a web search to find such a program and run it from pure
DOS. It will put out one of two numbers. If you get a "2308h" stepping, your
CPU is new enough to handle being upgraded. If you get "2305h", the CPU cannot
be upgraded.
When you do get an upgrade, you will be looking for one that clips
over the soldered 386SX chip. You might also find an upgrade that goes in
the math-coprocessor socket. Evergreen Technologies marketed an upgrade that
clipped over the soldered 386SX chip.
Other upgrades may also exist, but if you find one — make sure it is
compatible with an IBM PS/2 computer. Also, when you install the upgrade,
double check that the upgrade's pin 1 is oriented toward the installed CPU's
pin 1. If you get the orientation wrong, not only will the system not work, but
you may actually see sparks and smoke come from the upgrade, which will likely
ruin it. This might also ruin your planar, so be careful.
Memory upgrades: The 25SX planar comes with anywhere from 1 to 4 MB RAM
soldered on the planar itself. You can add one SIMM, up to 8 MB for a total of
up to 12 MB RAM. You may use IBM Parity 70 ns or 80 ns SIMMs for PS/2s to
upgrade the amount of installed RAM. These are fairly common and cheap in 2, 4,
and 8 MB sizes. You may also be able to convert
existing memory.
Solder "pads" for another SIMM socket exist on the 25 SX planar, but based
on the experiences of a comp.sys.ibm.ps2.hardware newsgroup member, installing
a socket there resulted in strange behavior and failure of diagnostic tests. If
you are really talented with a soldering iron or have professional soldering
equipment and a 1MB-only planar, you could add in the missing chips to get 4MB.
But this would take an extreme amount of soldering skill and is beyond the
scope of this page.
The 25SX has standard IDE and a standard 4 pin power connector plug-in on
the planar. You can use up to a 528MB hard disk, and beyond that with a disk
manager such as Ontrack's Ez-Drive program.
An SCSI card with a bootable ROM BIOS is also an option, but with the
performance of this system and the fact that it has IDE support already, it
probably won't make much difference in performance.
A Word About Model 25 Upgrade Planars
Locating and installing a CPU upgrade may be your best choice, but...
Update: Three upgrade boards exist for
certain:
The Reply Board upgrade planar is the be-all, end-all of Model 25 upgrades.
It features a true 486 CPU that can be upgraded to a 486DX4-100MHz CPU at best
as of this writing. Standard 72-pin parity SIMMs are used and Cirrus Logic SVGA
video is provided.
Trouble is, the Reply planar is rare at best, so you may have to do quite a
little bit of looking to find one.
Even rarer than the Reply board is IBM's EduQuest
7386 upgrade. This upgrade features a 386SLC processor operating at 20MHz.
IBM's manual for the 7386 hints at versions with other more powerful processors
being available, but I've never seen anything except the 4 386SLC-20 powered
ones I have.
Rarer yet is the PC Enterprises Genesis\PC board for the Model 25. This is
another replacement planar. I have recently acquired one of these from a kind
soul on the IBM PS/2 newsgroup, but I have yet to dive in and really work at
documenting it. PC Enterprises may still be in business, but as of this writing
their website appears to be nonfunctional.
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