segmented memory models

bfranchuk at bfranchuk at
Sat Aug 2 12:09:45 CDT 2008

Chuck Guzis wrote:
> Back around 1977, there was a lot of chatter about "16 bitters".  One 
> of the big issues for systems designers was the company behind the 
> chip.  National was horrible in terms of support (PACE).  TI 
> (TMS9900) wasn't much better.  GI seemed to be disintrerested in its 
> CPU (CP1600). DG didn't want to talk to people who might compete with 
> it (MicroNOVA) and Fairchild was loathe to admit that it even sold 
> the 9440.  All of the above suffered from one problem--64K address 
> space size.  
Lets not forget Dec did not have the 'home' computer idea at all
unlike the *PC*. I am now building a PC clone is seems again
as I want a 12/24 bit cpu using bit slice components from about
that same era ... 1978 ish. I am asumming 512x8 proms were
out by then. 16Kb x 1 drams was normal memory size of memory
chips. 512Kb of memory addressing is planned in hindsight
as compared to 256Kb (18 bits) as what could have been planed
had this computer been designed in the 70's. The only thing I
have done is made the  memory cycle  speed  .666 us  ( .333us)
access time  with  wait  states  for  the last  two  (4K)  pages of
memory. This gives me the best of both worlds ... slow I/O and
150ns memory chips for a clock speed faster than a PC .8 us.
 In this era of  megabyte memory chips is is easy to forget
the memory sizes that could  be  put on a printed circuit
> Cheers,
> Chuck
PS. I download a intel memory data book from bitsavers
from 1973 ( note more memory databooks could be usefull)
and marveled of  the small rack of 1mega-bit memory
made from 1kx1 drams compared to core of the same size.

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