Re: Memory design

Ed Casas (edc@ece.ubc.ca) Sat, 15 Apr 2000 11:41:43 -0700 

Date: Sat, 15 Apr 2000 11:41:43 -0700
From: Ed Casas <edc@ece.ubc.ca>
Subject: Re: Memory design



On Thu, Apr 13, 2000 at 03:04:46PM -0700, harry lee wrote:

> Why are bytewide memory components frequently preferred by the
> designers of small memory system and bitwide memory components
> preferree by the designers of large memory systems?

We select the width of the memory chips so as to minimize the
total cost.  The total cost includes chip, board and testing
costs.  All of these increase with the number of pins required to
implement the memory system.

The memory required for small memory systems can often be
provided by one or two chips and thus byte-wide components are
used.

Memories for larger systems will require more chips. By using
narrow (e.g. bit-wide) devices we can minimize the overall number
of pins required and thus reduce the overall cost.

For example, let's say we have to implement a 64kx8 (512 kbit)
memory using 128 kbit devices.  Each chip might be available as
either 16kx8 or 64kx2 devices.  In both cases we need 4 chips.
But the byte-wide devices will need 14 address plus 8 data = 22
pins each while the 'x2' devices will only need 16 address plus 2
data = 18 pins each.

-- 
Ed Casas   edc@ece.ubc.ca   http://casas.ece.ubc.ca   +1 604 822-2592