RE: [pups] Spares, et. al for 11/44 system - TUHS

8 Mar 2001

Greg,

...
  Thought about that too but the math doesn't work.
 40+64 chips = 104
 chips * 65536 bits per chip = 6815744 total bits.

 6815744 doesn't divide cleanly by any of 9, 18, 19, 36, or 38 Right... 12 bits
of ECC seems a bit much.  Dunno what that stuff is
about... weird! ;)

Fred

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To: greg(a)ciswired.com, pups(a)minnie.cs.adfa.edu.au
Subject: Re: [pups] Spares, et. al for 11/44 system
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  Date: Tue, 6 Mar 2001 20:07:00 -0500 (EST)
 From: "Gregory R. Travis" &lt;greg(a)ciswired.com&gt;
 To: pups(a)minnie.cs.adfa.edu.au
 Subject: [pups] Spares, et. al for 11/44 system

 p.s.  The Nat. Semi board is a bit strange.  It has an area of
 16x4 TI 64K-bit chips (i.e  64x64k/8 = .5MB) and another
 area of 10x4 TI 64K-bit chips (i.e. .3MB).  No matter
 what I do, I can't do the math to get this board to
 fit into a 256/512/1MB size.  I ASSUME it's a .5MB
 board, but what about the extra chips? 
Nat.Semi. used to make ECC memory boards for the PDP11.

I had one once, it looks like you have one now.  My arithmetic says 5
extra bits per 8-bit byte makes for single-error correcting, dual-error
detecting ECC on the byte level.  Vaxes do it with 39 bits per 32-bit
word, Alphas do it with 72 bits per 64-bit word.  Economy of scale.

As I remember, you could just ignore the ECC and it would work like
a standard parity memory board, except that it very rarely had any
parity errors.

    carl

        carl lowenstein         marine physical lab     u.c. san diego
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