HP Laserjet ..again....

From: Patrick Finnegan <pat_at_computer-refuge.org>
Date: Sun Sep 19 16:03:48 2004

Tony Duell declared on Sunday 19 September 2004 01:39 pm:
> > Sure the buss width matters if you are measuring memory as it is
> > NORMALY measured, in Bytes, not Bits.
> No it doesn't.
> Suppose I take 16 of the 64K * 1 DRAM chips (4164s). I wire them up to
> an 8 bit databus with the apporporate control electronics so I get
> 128K 8 bit locations. That stores 128K bytes.
> I now wire them up differently to a 16 bit data bus system. I haev 64K
> 16 bit locations. That's _still_ 128K bytes of storage.

Yes, but it does matter if the memory is ECC or something. 9 x 1Mbit
chips doesn't (typically) give you 1152KB of ram, it give you 1024KB.
The same goes for ECC, and the memory used in old (on-topic) IBM
RS/6000s which is 40 bits wide (ECC + a spare bit). a 2M x 40bit module
has 8MB of ram, not 9MB.

Also, I guess, it's not proper (at least in my opinion) to say a PDP-8
with 32kW of 12bit wide memory has 48KB of ram.

However for multiple of 8 (or 9 with byte-parity or ...) bus widths, the
bus width doesn't really matter with how many bytes the memory contains.

Purdue University ITAP/RCS        --- http://www.itap.purdue.edu/rcs/
The Computer Refuge               --- http://computer-refuge.org
Received on Sun Sep 19 2004 - 16:03:48 BST

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