A LOW COST PERFORMANCE BOOST FOR YOUR 386 PC

If you own a 386 based PC, you may be a little envious of the owners of all
these speedy new 486 based PCs. I know that I was. I say WAS because I
now get 486 class performance out of my old 386 system and I did not
spend a fortune. If you have a 386 system you may also be interested in
this upgrade.

THE Cx486DLC

Introduced in the summer of 1992, Cyrix produces a processor called the
Cx486DLC.  The Cx486DLC is a cross between Intel's 386DX and 486SX.  The
Cx486DLC is pin compatible with the 386DX and instruction set compatible
with the 486SX.  Like the 486SX the Cx486DLC contains an internal cache
and an optimized execution unit.  The cache and optimized execution unit
are the main reasons that a 486 is faster then a 386 at the same clock
rate. By replacing your 386 CPU with the Cx486DLC you get 486 class
performance without replacing your PC.

To be sure that your PC is upgradable to the Cx486DLC, check through the
following:

1 - The PC must be based on a 386DX (sometimes called a 386 or 80386)
from Intel or AMD.  PCs based on the 386SX can not use this upgrade. 

2 - Remove the cover of your PC and locate the CPU.  It is a 1.5 inch
square IC.  It should be labeled Intel or AMD 386DX.  There must be
about 2 inches of open space above the CPU.  The Cx486DLC runs hotter
than the 386DX and typically requires a heat sink mounted on top of the
chip. The additional space is required by the heat sink.

3 - You should have a socket on the motherboard for a 387 math
co-processor. You may have a 387 already installed.

If your PC meets all of the above requirements you can perform the
upgrade.  I checked around for the best prices on the Cyrix chips and
found that CompuAdd express offers the best deal.  They sell upgrade
kits for their line of scalable PCs.  Each upgrade kit includes the
Cx486DLC, a Cyrix math co-processor, the heat sink and a chip puller for
removing the old 386 CPU.  While they are intended for use with
CompuAdd's line of PCs, they are ideal for our upgrade and are quite a
bargain.  At the time I'm writing this, the price of a 33 Mhz upgrade
kit has just dropped to $159 and a 40 Mhz kit has dropped to $249.  A
math co-processor alone costs about $100.  The upgrade kit to order if
your PC runs at 33 Mhz or slower is the 433DLC.  The 40 Mhz kit is the
440DLC. 

PERFORMING THE UPGRADE

Remove the cover from your PC, locate the 386 CPU.  Note the location of
pin 1 on the CPU.  Pin 1 is marked by a dot or cut off corner on the
chip.  Use the chip puller to carefully pry the CPU out of it's socket. 
Work slowly around the chip as to not bend any of the pins.  Place the
486DLC into the socket with pin 1 in the same orientation as before. 
Carefully press the chip into the socket.  Once the chip is in place,
power on the PC, it should beep and power up normally.  Power down the
PC, install the heat sink on top of the Cx486DLC and install the math
co-processor as instructed in the manual for the PC (you may need to
move a jumper in addition to installing the chip).  Replace the cover
and you are ready to go.  The PC should now run normally.  To get the
full speed increase you will also need a program that activates the
Cx486DLC's cache.  I've written such a program, called CYINIT.  You
download a copy of CYINIT (in the archive 386486.ZIP) from both
Compuserve or Genie.  It is in the IBMAPP section on Compuserve and in
Don Lancaster's PSRT on Genie.  If would like a copy on disk, I will
provide one if you send me a check for $10.00.  Once the system is up
and running add CYINIT to your autoexec.bat file.  That way the cache
will automatically be activated when you start your PC. 

THE PERFORMANCE IMPROVEMENT

I've upgraded several systems and found that the CPU performance
typically improves about 50%. Figure 1 shows the typical improvement
shown in the ZD Labs benchmark tests. The system upgraded was a 33 Mhz
386DX with a 64 K external cache and an Intel 387 math coprocessor (also
called an FPU - Floating Point Unit). The performance improvement varied
with the different tests, but averaged out to about a 50 % improvement.
The FPU test also showed that the Cyrix math coprocessor offered a large
speed gain over the Intel math coprocessor. Figure 2 compares the
performance of a 33 Mhz 386, a 33 Mhz Cx486DLC, a 33 Mhz 486DX, a 40 Mhz
Cx486DLC and a 66 Mhz 486DX2 running the 386 instruction mix from the ZD
Labs benchmark. As it shows the 486DLC gives 486 class performance to
your old 386 PC at a bargain price.

RESOURCE LIST

Cyrix
2703 North Central Expressway
Richardson, Texas 75080

In my article on upgrading your 386 PC to a 486. I recommended CompuAdd
Express as the best place to purchase the upgrade. Just recently
CompuAdd has shutdown the Express division and the upgrade kit is no
longer available from them. In scanning through the Computer Shopper I
have found the following list of vendors that sell the Cyrix CPUs ( I
have have not dealt with any of these outfits so these are not
endorsements on my part):

Buffalo Products	1-800-345-2356

L.A. Trade		1-800-433-3726

Nevada Computer		1-800-892-2928

Treasure Chest		1-800-677-9781

PC Importers		1-800-886-5155

In addition the Cyrix distributors are:

Bell Micro Pro		1-800-955-1999

Bell Industries		1-800-BUY-BELL

I hope that these numbers could be published in the next edition to aid
those looking to upgrade.

Robert G. Brown
30 Wicks Road
E. Northport NY 11731

