64bit data 128Bit address...Re: Building a Z-80 (64bit! - test-drb@ccmp.vtda.org

26 Oct 1998

...
 > "Max Eskin" &lt;maxeskin(a)hotmail.com&gt;
wrote:
>> No application _requires_ any number of bits > 1. It's a question of
>> performance. After all, a Z80 could have 512M RAM, just not
>> contiguously (and would probably require a lot of hardware to access
>> it).
>
> OK, then the Z80 system will require 19 bits of address.  Sure,
> some of those bits aren't coming directly out of the CPU, but
> they're coming from somewhere. 
...
  Actually the figure is 29 bits (it was 512M not 512K)
but I agree with you
 100% in principle. 
...
  The way I look at it is this:  [...] 
...
  I therefore see address buses growing at 16 bits every
30 years.  That's
 just over a bit every 2 years - slower than I expected but not much.
 Someone (I forget who) said that memory chips double in capacity every 18
 months.  This would give 16 bits in 24 years. 
Interesting szenario, especialy when connected to the Mores Law
(didn't he tell this regarding integration ?).

...
  I claim that the assertion that we'll see even
64-bit address spaces being
 used anything like up by 2003 is unfounded.  According to that growth rate
 above, we will start hitting the limit of 48-bit addressing - 256 TWord -
 in the '20s, and the limit of 64-bit addressing, 16 exawords (or exabytes,
 possibly), in the '50s (or '40s at 1 bit per 18 months).  Many of us will
 probably still be alive then (I shall be celebrating my 83rd birthday in
 March of 2050 ) 
Hmm I will have my 88th by then - jets join :)

...
  - and I for one would like to see what sort of
technology
 will be used to store 16 exabytes in a space smaller than a mountain! 
The size isn't the real problem - you already get 16 Gig in less
than 320 cm^3 (using hard disk technology) which is more than
100 Meg per cm^3, which gives us 100x100x100x100 Meg or 100 Tera
per m^3 (Only heat will be a problem, but if we assume that this
will shrink by the factor 2 within the next few years, we get
enough space for cooling without developing a new technology).
100 Tera are 100x2^40 Bytes so, for 16 exabytes you need
10x2^18 m^3 or 64x64x64x10 m^3 - just the size of a ordinary
160 store skyscraper. Nothing real big - isn't it? - and especialy
not a mountain. and if we assume a increasing density by 10 within
the next years, it is less than a warehouse.

This is all just (near) todays technology - the real problem
is the access time .... A wire could come up to 100m between
a starage device at the perhipherieal area and a 64 Bit computer
in the middle - 100m thats just 1/3.000.000s or 333ns traveling
time ... seams we have created some kind of piplineing prior
to the CPU :) So, calulating a 1 us round trip time, we just
could runn a 4 MHz Z80 ... hmm didn't he ask for 64 Bit Z80 ?

(I just left the disc acces time out of calculation, but acording
to any information availabel from disk manufacturers the internal
caches will eliminate this almost to zero :)

Gruss
Hans

P.S.: for 128 Bit address range we just have to enhance the building
by a bit more than 1.000.000 in each direction. Giving a size of
5x128.000.000x128.000.000x128.000.000 m^3 or
5x128.000x128.000x128.000 km^3 compared to volume of earth
   20.000x 20.000x 20.000 km^3 (just my memory)
And dont forget the traveling time of signals of something like
.6 seconds across the cube.

--
Ich denke, also bin ich, also gut
HRK