23 Nov
2000
23 Nov
'00
4:29 a.m.
> Try asking programmers what width processors are
instead of hardware
> engineers. They'll tell you that the 8080 and Z-80 are 8-bitters, and
> that the 68000 and IBM 360 (most models) are 32-bitters.
Nope, any programmer who cares how fast their code
runs will let you
know that the 68000 is a 16 bitter. It's not like I've never coded
for 68K. I certainly prefer it to intel. That doesn't make it
32 bit.
Earlyer you defined the 68008 as 16 Bit - just, the timing
influence of the 8 Bit bus is several times the one of the
ALU, so where to go ?
A CPU is always the implementation of an ISA, and thus the
may use a vide variety of details which all together doesn't
matter for the programmers view. If you have to count cycles
to perform your task, you're not doing (for instance) 68K
code, but rather code for a 68xxx Version Y stepping Z.
> > No, every x86 chip since the original 386 is
a 32 bit CPU since
> > the width of the integer ALU is 32 bits.
> Actually there is a 64-bit integer ALU in most
recent x86 processors.
> Describing where it is and what it does is left as an exercise to
> the reader.
Are you talking about the use of the floating point
unit for integer
multiplies and the addition of MMX/SSE stuff?
Jep - there's a seperate ALU for 64 Bit integer, including a
seperate register set for its operation. the MMX Unit is _not_
part ot the FPU - the MMX data registers are only _mapped_ to
the FPU registers - this trick has be invented to make the
MMX-Unit compatible to task switching in existing multi tasking
OSes - making the new register set visible as seperate entity
would have made MMX unusable on these systems until a new
task switcher was ready to switch also MMX content - which
may have taken years (Windows) or would never happen on some
systems - remember how long it took for PC Unixes to recognize
and support 287s and up.
I don't think that
qualifies. The bulk of integer operations are still done 32 bits at
a time.
Now what ? So 'the' bulk ALU is the one to take ?
Gruss
H.
Ps:.: I love it :)
--
VCF Europa 2.0 am 28./29. April 2001 in Muenchen
http://www.vintage.org/vcfe
http://www.homecomputer.de/vcfe