[pups] Spares, et. al for 11/44 system
Carl Lowenstein
cdl at mpl.ucsd.edu
Thu Mar 8 07:15:48 AEST 2001
> Date: Tue, 6 Mar 2001 20:07:00 -0500 (EST)
> From: "Gregory R. Travis" <greg at ciswired.com>
> To: pups at 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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