80287 vs 80287XL

[iguana]

There is an discussion at local (Russia) forum about 287XL

All the way I thought XL is just 12,5 MHz CMOS version of 80287.

but wiki says:
...an 80287XL, which was actually an 80387SX with a 287 pinout.

http://en.wikipedia.org/wiki/X87

Is this true ???
Will be 287XL faster than 80287 at the same mobo with say 286-10 ?

[gshv]

It should be. I quickly scanned through 80287 and 80287XL datasheets, and here performance/instruction set differences I found:

- XL processor is almost twice as fast when executing basic arithmetic instructions (add, sub, mul, div).
- other instructions, such as load, store, special, etc, could be slower or faster depending on the instruction, operand type, etc, but on average they have comparable execution time to 80287.
- The 80287XL divides external frequency by 2, while the 80287 divides it by 3. Because of this, when the XL processor is plugged into 80287 socket, it will run at 50% higher frequency than the 80287.
- The XL has a few additional 80387 instructions - sin, cos, etc.

Gennadiy

[susl45]

[zape]

[debs3759]

[debs3759]

Took 30 seconds to find that in Google

[zape]

There is no information on the divider

[debs3759]

There is no info on the divider on that site, but it does show documented performance data compared to the 287XL, and it clearly indicates that the Cyrix chip executes code faster than the XL

[frag_]

coproc.txt:

[i440bx]

*dig out an old thread*

I can confirm everything gshv wrote. I am bulding a 286 System - and have two 287ers tested.

Pic 1 "D80287-6" - a D80287-6

Pic 2 and 3 the C80287XL

Its a 387 in an old shell