23 Oct
1998
23 Oct
'98
5:29 a.m.
Just tell me why ? Because it has been the tame with
old
8 Bit uPs ? Come on thats just the stupid 'thats the way
it always has been' idea. Address bus shuld be a) as wide
as needed and b) if possible not exeeding the Size of the
basic data unit.
Again I say, You are not thinking about the future! "As wide as needed"...
Is a very NOW statement.
For a) just tell me where you need more
than 4 Gig, or better where you need _way_ more than 4 Gig,
because just 4 or 10 times this address space is easyer done
with paging methods (wait for b)).
Wait for Windows 2003! I'm sure that'll take at least 1Gb. And MS Office
2006 Hell, there's another 1 Gb. (Yes, I gotta poke at MS)
And for b) you need
special logic to perform address calculation, you can't
hold one address in one regular register, you need more
silicon to implement the adressing logic, adress calculation
and (hidden) adressing register - you also need an additional
ALU.
More Silicon!?!? Where has this discussion gone awry???? I wanted to
build a board the that was a Processor unit that talked Z-80. As for the
notion of making a chip.... The chip size would not change. Yes the used
real-estate would but you have that real-estate anyway.
If you keep
thinking like "you'll need $16,000,000,000.00
in memory for that address size" you'll do the same stupid thing as:
If you don't need it don't spent the silicon. Micro$oft
("640K is more than enough for anyone"),
Be carefull, now you're entering historical teretorry.
MS-DOs was designed to use the full 1 Meg address space
of the 8086/88. And could could well boot with something
like 900 and more K user mem available. The 'Barrier'
(640 or what ever) was given to DOS by the BIOS of the
respective machine. And the PC-Bios had just to obey the
CGA memory. old
programmers ("year 2000 is 20 years away.
This stuff will be obsolete by then"),
You are just talking to one of them - and FYI we continue
to use systems with two digit years and they are Y2K ready :) and let us not
forget Intel with their screwy memory addressing
schemes on their pre-X386s.
Again, please think a bit - the x86 segmentation is a real
great atempt to give
- give more than 64 K Mem to a 16 Bit uP Think ahead!
It wouldn't cost that much more or requrie much
more effort to add a few bits to the address bus.
Just remember b) you NEED more effort, especialy things
that don't fit into your standard model.
And if your thinking about MMUs to expand a 64 Bit adress
to 128, you just cut the adressrage down to 64 Bit, since
external address enhancements are no design detail of a CPU. As for the
suggestion of using a DEC alpha to emulate a Z-80... I thought
about it but, those darned Alphas are way too expensive for us hobbist.
Please ? An Alpha board with CPU is only a bit more expensive
than a PC board with an equal Pentium. At least thats the
street price over here in Munich - we have some PC part shops
that are also selling Alpha boards and CPUs right aut of the
blister. Anyone know if
Zilog is going to beef up the Zx80 line????
Faster 180s and of course the 380s. But Zilog has to
build things that will sell, so they are more into
integrating special I/O devices than more CPU power.