Intel 8087 Math Co-Processor


Some people are under the impression that adding an 8087 chip to their IBM 5150/5155/5160 motherboard will speed up their computer.
That impression is false.
The 8087 does not speed up hardware.  It will speed up software that is written to take advantage of the presence of an 8087.

The following threads at the Vintage Computer Forums discuss such software:

Thread #1     ("Software which can use 8087/80287 coprocessor?")
Thread #2     ("Programs that use the 8087")
Thread #3     ("Programs that use the 80287")


Motherboard switch change required

IBM indicates that after an 8087 is fitted to the IBM 5150/5155/5160 motherboard, switch 2 on switch block SW1 is to be set to the OFF position.  See here


Speed rating

In the IBM 5150/5155/5160, any 8087 fitted needs to be rated at 5 MHz, or faster (because the motherboard runs the 8087 at 4.77 MHz.)

Printed on chip	Speed rating
C8087 4MHZ	4 MHz	Unsuitable.  Photo at here.
C8087	5 MHz
D8087	5 MHz	Prefix of 'D'
C8087-3	5 MHz
C8087-2	8 MHz
D8087-2	8 MHz	Prefix of 'D'
C8087-1	10 MHz
D8087-1	10 MHz	Prefix of 'D'

The speed rating is not how fast the chip runs.  It is a 'maximum that chip is to be run at', akin to the speed rating of car tyres.  For example, even if you put a 10 MHz rated 8087 into your IBM 5150/5155/5160, the motherboard will still only run the chip at 4.77 MHz.


Aliases

Intel refers to the chip as, 'Math CoProcessor'.

Some other names are:

•	Numeric Processor Unit, abrieviated as NPU.   (Pattern: CPU, NPU, GPU) Some PC diagnostic software, such as CheckIt, uses 'NPU' instead of 'Math Co-Processor'. Total Hardware 1999 uses 'NPU'.
•	Numeric Data Processor, abrieviated as NDP, as seen in some Toshiba laptop manuals.
•	Numeric coprocessor, as used by the Landmark/Supersoft diagnostics.