Core memory Re: Old farts and new Linux

[Lamar Owen]

> What you probably saw was a 16*K* byte memory, the boards from the late
> 60s were typically around 16K bits, 8 boards to a byte, and about as big
> on a side as a tower case with the small scale integration driver chips
> around the sides of the core fabric.  A 16MB machine would have been
> gargantuan, indeed;  I would guess 100 or more 19inch racks, 8 feet tall,
> and probably costing on the order of $50M in current dollars.

I have an 8Kx12 core plane here from a PDP-8. Fairchild 7446 drivers and a 
discrete sense amplifier driving a 74128.  The core plane itself is about 5x5 
inches, and the card is 15 1/2 x 7 3/4 inches.  I don't have the omnibus card 
(H212) the plane card attached to; I threw it away long ago, just keeping the 
core board itself.  The plane is DEC H219-2779, dated 6/2/1975.  For those 
PDP-8 buffs out there, no, I don't have the CPU any more; I sold it back in 
1990 for a good price...

As a trivia data point, elderly seamtresses were employed in the manufacture 
of some core stacks, since these stacks were hand-sewn.  Elderly seamtresses 
were preferred since they could 'stitch' a stack with fewer errors than a 
machine could.  'Has anyone seen my knitting?'  The accuracy of experienced 
seamstresses in doing crochet or knitting (or quilting, etc) is legendary.

Another interesting thing about core: it is nonvolatile (but dynamic).  While 
every read of the core required the data to be written back (the read was 
destructive), core doesn't lose its mind at power-off.  This core plane still 
has a program loaded: you can see the pattern due to magnetic attraction and 
replusion of adjacent bits.  And writing was just a special case of reading.

Hmmm, 16 MB of H219 stacks would occupy 16x8x2x2048x2 cubic inches, just for 
the cards.  That would be 1,048,576 cubic inches.  The standard 19 inch EIA 
rack at 8 feet tall that is 26 inches deep (a fairly deep rack) can contain 
roughly 47,424 cubic inches, yielding 22.1 racks.  23 racks would be enough 
for the core and the CPU, but then you'd need another 2 racks for the power 
supplies.  So about one quarter of your estimate.

For more information on PDP8 stuff, see both pdp8.org and pdp8.net, where you 
can even download the manuals...  See 
http://highgate.comm.sfu.ca/~djg/htdocs/cgi-bin/tifftopdf.cgi/mm8aa.pdf?pages=1-5&loc=newstuff 
for a pdf of the schematics for this module.
-- 
Lamar Owen
Director of Information Technology
Pisgah Astronomical Research Institute
1 PARI Drive
Rosman, NC  28772
(828)862-5554
www.pari.edu