On Sun, Feb 8, 2009 at 17:57, Nathan Andelin <nandelin@xxxxxxxxx> wrote:
and noticed that the AS/400 had only 96 meg, total. And it was hosting about 30 terminals. That blew me away, too.
As far as i have understood the OS/400 architecture (and i'm wrong:
please correct me here - there are people on this list that know far
more about this than me), memory is never used explicitly - this is
because of the single level storage system. Instead, the bits adressed
are always on-disk somewhere (or not yet, if not explicitly
synchronised). Memory just acts a giant disk cache, if compared to
other architectures like Windows, Linux or AIX, where memory is
explicitly adressed and allocated (and the "hack" of swapping was
invented to use more memory than is physically installed).
This will allow the IBM i to work with even extremely low amounts of
memory compared to other architectures, but obviously with a brutal
degradation of speed. However, as long as 5250 is used this can be
negligible as the system does not have to directly interprete data
entered on the 5250 terminal, instead the data is sent to the IBM i
screen-by-screen instead of key-by-key like vt100 terminals did.
However, this also explains why extremely low performance machines
like a 500 CPW POWER5 520 with 2x 36GB arms and 1024MB of RAM could
actually be used to work on, can become absolute money eaters when you
have to actually do maintenance on them. Just last month i upgraded
such a system from V5R3 to V6R1 - took me the better part of a
weekend, most of which i spent in front of the console waiting for the
system to actually do something.
midrange.com
