modern stuff

[Gordon Henderson]

On Fri, 26 Oct 2018, emanuel stiebler via cctalk wrote:

> On 2018-10-25 14:48, Chuck Guzis via cctalk wrote:
>
>> While this was a failure on a spectacular level, it was by no means the
>> only misstep by Intel.   The i860 RISC CPU at one time was even being
>> endorsed by BillG as a possible personal computer basis.
>
> the i860 found at least a little niche on graphics boards, so somehow
> not a complete failure ;-)

I worked for a company that made supercomputer boards out of the i860 at 
one point - at the time (very early 90's) they were blindingly fast, 
40Mhz, 3 instructions per clock cycle which, since one was a floating 
point multiply and add meant that it was pretty good - at the time.

However it was a royal PITA to code for although a 32-bit CPU, it would 
read memory 64 bits at a time (actually 128 IIRC to satisfy the cache), 
with half that 64-bit word being an instruction for the integer unit and 
half for the floating point unit, so you effectively had to build a 
floating point pipeline by hand coded instructions, so 8 (I think) 
instructions to load the pipeline, then each subsequent instruction would 
feed another value into the pipe, then another 8 at the end to empty it. 
Great for big matrix operations, rubbish for a single add of 2 FP numbers.

The issue came when you wanted to take an interrupt - the overhead of 
flushing the pipe, reloading it all for the next context, and so on really 
bogged it down.

Not to mention writing assembly code in 2 columns...

There were quite a few systems built with about 30 boards in them, each 
having 2 x i860's and a good few MB of RAM (64MB I think) built.

-Gordon