RE: Where is IBM?

["Joe Pluta" <joepluta@xxxxxxxxxxxxxxxxx>]

> From: Walden H. Leverich III
>
> Of course, under the covers IBM can do some stuff with larger allocations,
> but under the covers they must also respect the difference between "real"
> memory and disk. And the iSeries only supports half the memory of
> a Windows box.

Not gonna fight, Walden, because it's too long and tiring.  Your use of the
word "supports" has to do with the fact that Windows uses physical memory,
whereas OS/400 uses a virtual address space.  I really don't want to take
the time to explain the difference between physical memory and addressable
memory space, but I'll give it one shot.

Windows is constrained by its physical memory, the limit of which has JUST
been upped to 39 bits and again, we have no idea how that has been
implemented in the APIs - what I read implies that only a few APIs support
this sort of addressing.  But even so, this simply means that, if you were
willing to spend the money (roughly $75K for the full 512GB of cheap memory,
or closer to $200K for RDRAM), you could theoretically index a file of
around half a terabyte.

OS/400 uses a completely virtual address space, though Leif asserts that the
usable AS/400 memory space is about 50 bits.  This is still roughly 1000
terabytes, and is far above anything Windows can even dream about.  Because
of the virtual memory scheme, the AS/400 can have a file with terabytes of
data that the operating system will page in and out, index, and so on,
completely transparently to the programmer.

I hope this explains my point, because if it doesn't, I'm not up to the job
of explaining it.  These are the discussions that make it crystal clear to
me that OS/400 is light years ahead of PC operating systems, and if you
disagree, then it's unlikely that anything I say will change your mind.

Joe