🚀 go-pugleaf

Colin Plumb writes:
  >
  > ... i860 ... could lay claim to being ... 64-bit microprocessor.
  > It has a 64-bit external bus, and a fair number of 64-bit operations.
  > It still has 32-bit addresses and 32-bit integer registers, but the
  > floating point unit and the (to my mind, very wierd) graphics units
  > are 64 bits internally.



I suspect that many folks believe you gotta have N bit integers and
>=N bit addresses to legitimately be called an N bit processor.


Fodder for thought-experiments:

   Intel 8086/7 had 16 bit external bus, 16-bit integers, and an 80-bit
   floating point unit.  Yet it is considered to be a 16-bit machine.
   Addresses are 16 bits plus extra sophistication :-) due to segments.

   B-5000 SPARC chip (ECL from B.I.T.) has 64 bit external bus, a 64 bit
   floating point unit, 32 bit integers, and 32 bit addresses.  Just
   like the i860.  Yet SPARCs of today, B-5000 included, are typically
   called 32 bit machines.

   Intel 432 had an 80 bit floating point unit, 32 bit integers, and a
   16 bit external bus.  Addresses were >=40 bits.  Four different
   numbers, quite fun :-).  Typically it is called a 32 bit machine.

   Top of the line VAXes have >64 bit external busses, >64 bit floating
   point units, and 32 bit integers.  Usually the VAX is called a
   32 bit machine.


Opinion: I speculate that the 8088 caused all of this confusion.  It is
         a 16-bit machine which marketeers wrongly labelled "an 8 bit
         processor" and the misinformation stuck.

Question: If a student did a MOSIS chip that implemented the PDP-8 with
          a doubleword (24-bit) interface at its pins, would that
          reclassify the PDP-8 as a 24 bit computer?  Remember that the
          PDP-8 floating point included formats > 12 bits.
-- 
 -- Mark Johnson	
 	MIPS Computer Systems, 930 E. Arques, Sunnyvale, CA 94086
	(408) 991-0208    mark@mips.com  {or ...!decwrl!mips!mark}