Intel 8087 Math Co-Processor

Some people are under the impression that adding an 8087 to their 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

After fitting an 8087 to the IBM 5150/5155/5160 motherboard, switch 2 on switch block SW1 needs 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.

Printed on chip Speed rating  
C8087 4MHZ 4 MHz  Unsuitable.  Photo at here.
C8087 5 MHz  
C8087-2 8 MHz  
C8087-1 10 MHz  

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.  Even if you put a 10 MHz rated 8087 into your 5150/5155/5160, the motherboard will still only run the chip at 4.77 MHz.


Intel refers to the chip as, 'Math CoProcessor'.
However, chips like these were often referred to generally as a Numeric Processor Unit, which is often abrieviated as NPU.   (Pattern: CPU, NPU, GPU)

Some PC diagnostic software, such as CheckIt, uses 'NPU' instead of 'Math Co-Processor'.