From mboxrd@z Thu Jan 1 00:00:00 1970 From: Fred.van.Kempen@microwalt.nl (Fred N. van Kempen) Date: Wed, 7 Mar 2001 19:36:02 +0100 Subject: [pups] Spares, et. al for 11/44 system Message-ID: <6F63E31101C6D41196490008C7B2BFC32D39@mwnt4.microwalt.nl> 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 ********************************************************************** This email and any files transmitted with it are confidential and intended solely for the use of the individual or entity to whom they are addressed. If you have received this email in error please notify the system manager. This footnote also confirms that this email message has been swept by MIMEsweeper for the presence of computer viruses. www.mimesweeper.com ********************************************************************** Received: (from major at localhost) by minnie.cs.adfa.edu.au (8.9.3/8.9.3) id IAA27971 for pups-liszt; Thu, 8 Mar 2001 08:20:35 +1100 (EST) (envelope-from owner-pups at minnie.cs.adfa.edu.au) Received: from chiton.ucsd.edu (chiton.ucsd.edu [192.135.238.128]) by minnie.cs.adfa.edu.au (8.9.3/8.9.3) with ESMTP id IAA27966 for ; Thu, 8 Mar 2001 08:20:30 +1100 (EST) (envelope-from cdl at mpl.ucsd.edu) Received: (from cdl at localhost) by chiton.ucsd.edu (8.9.3/8.9.3) id NAA15151; Wed, 7 Mar 2001 13:15:48 -0800 (PST) Date: Wed, 7 Mar 2001 13:15:48 -0800 (PST) From: Carl Lowenstein Message-Id: <200103072115.NAA15151 at chiton.ucsd.edu> To: greg at ciswired.com, pups at minnie.cs.adfa.edu.au Subject: Re: [pups] Spares, et. al for 11/44 system Sender: owner-pups at minnie.cs.adfa.edu.au Precedence: bulk > Date: Tue, 6 Mar 2001 20:07:00 -0500 (EST) > From: "Gregory R. Travis" > 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 {decvax|ucbvax} !ucsd!mpl!cdl cdl at mpl.ucsd.edu clowenstein at ucsd.edu Received: (from major at localhost) by minnie.cs.adfa.edu.au (8.9.3/8.9.3) id SAA32608 for pups-liszt; Thu, 8 Mar 2001 18:55:06 +1100 (EST) (envelope-from owner-pups at minnie.cs.adfa.edu.au) Received: from mserv1c.vianw.co.uk (mserv1c.vianw.co.uk [195.102.240.33]) by minnie.cs.adfa.edu.au (8.9.3/8.9.3) with ESMTP id SAA32604 for ; Thu, 8 Mar 2001 18:55:03 +1100 (EST) (envelope-from pete at dunnington.u-net.com) Received: from p113.nas4.is5.u-net.net ([195.102.201.241] helo=indy.dunnington.u-net.com) by mserv1c.vianw.co.uk with smtp (Exim 3.22 #5) id 14avBh-0000Ji-00 for pups at minnie.cs.adfa.edu.au; Thu, 08 Mar 2001 07:50:17 +0000 Received: by indy.dunnington.u-net.com (951211.SGI.8.6.12.PATCH1502/980207.PNT) for pups at minnie.cs.adfa.edu.au id WAA24282; Wed, 7 Mar 2001 22:10:25 GMT Date: Wed, 7 Mar 2001 22:10:25 GMT From: pete@dunnington.u-net.com (Pete Turnbull) Message-Id: <10103072210.ZM24280 at indy.dunnington.u-net.com> In-Reply-To: "Gregory R. Travis" "RE: [pups] Spares, et. al for 11/44 system" (Mar 7, 7:59) References: X-Mailer: Z-Mail (3.2.3 08feb96 MediaMail) To: pups at minnie.cs.adfa.edu.au Subject: Re: [pups] Spares, et. al for 11/44 system Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 8bit Sender: owner-pups at minnie.cs.adfa.edu.au Precedence: bulk On Mar 7, 7:59, Gregory R. Travis wrote: > 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 It divides by 13, though (64K x 13 x 8, so the prime factors are 2 and 13). Unlikely as it sounds, could this be for a 12-bit word machine? 13 is not only 12+1, it's 8+5. 5 is a common number of bits for ECC (though not, I admit, for 8-bit words! Usually it's 8+3, 16+5, or 16+6). It also strikes me as odd that a NatSemi board should have TI chips on it. NatSemi made their own RAM, and Texas made their own PDP-11 and Vax memory boards. -- Pete Peter Turnbull Network Manager Dept. of Computer Science University of York