Re: Memory Upgrade

From: <thomas@inorbit.com>
On Tue, 25 September 2001, "Draper, Dale" wrote:
> Why exactly is it that IBM does not use PC standard memory chipsets?

Maybe someone else can say it better but AS/400s need special memory. Every
64 bits of AS/400 memory are accompanied by a special-purpose 65th bit, the
'tag' bit. In short, this extra circuitry provides critical function such as
'tagging' pointers in memory so that they cannot be modified except through
approved interfaces. This is a major part of hardware security enforcement
and the kind of thing that sets AS/400s apart. Such memory can be used on
various other PowerPC systems that can run in 'tags inactive' mode, buth
other memory cannot be used in AS/400s.

===> Tom, you are overstating the case a bit:
1) the tag bit could be stored in a byte, meaning that no special memory
bandwidth
is needed.
2) the tagged pointer protection is not hardware, but is done in software, so
need
not contribute to make memory more expensive.

As we all know, the reason AS/400 memory is so expensive is simply that IBM
charges for it what the market will bear (as per its monopoly position);
this is called "milking the cow".