Intel 80287 Math Co-Processor


Some people are under the impression that adding an 80287 chip to their IBM 5162/5170 motherboard will speed up their computer.
That impression is false.
The 80287 does not speed up hardware.  It will speed up software that is written to take advantage of the presence of an 80287.

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

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


Package required

Both the IBM 5162 motherboard and IBM 5170 motherboard require the 80287 to be in a 40-pin DIP (dual inline package) package.


SETUP change required

IBM indicates that after fitting an 80287 to the IBM 5162/5170 motherboard, you will need to perform SETUP (CMOS SETUP) indicating that there is now a math co-processor fitted.
If you fail to do that, some software (e.g. diagnostics) may report that a math co-processor is not fitted.


Speed rating

In the IBM 5162, any 80287 fitted needs to be rated at 5 MHz, or faster (because the motherboard runs the 80287 at 4.77 MHz.)  [diagram]
In the 6 MHz version of the IBM 5170, any 80287 fitted needs to be rated at 4 MHz, or faster (because the motherboard runs the 80287 at 4 MHz.)
In the 8 MHz version of the IBM 5170, any 80287 fitted needs to be rated at 6 MHz, or faster (because the motherboard runs the 80287 at 5.33 MHz.)  [diagram]

Printed on chip	Speed rating	Comment
Intel C80287-3	5 MHz	Prefix is C, not D
Intel D80287-6	6 MHz
Intel D80287-8	8 MHz
Intel D80287-10	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.  For example, even if you put a 10 MHz rated 80287 into your IBM 5162, 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.