• Subject: Re: RPG400 SDA query?
  • From: Jon Paris <paris@xxxxxxxxxx>
  • Date: Sun, 26 Oct 1997 21:07:31 -0500

>>> This is a question based upon what I was told once:  I was told that one
reason the AS/400 is so stable and the file structure is so stable is that it
is not a pointer-based system.   Now I suspect that may have been an
old wive's tale.  So...  how come we don't use a PC-based file system?<<<

It would be next to impossible (if not impossible) to create a system that
didn't use pointers at all.  It's not whether you can use them that matters,
it's what you can do with them once you've got them!

The reason the AS/400 is stable has to do with the fact that pointers include
permission/access right type information that ensures that they cannot touch
things that they have no rights to go near.  That's why an AS/400 pointer is 16
bytes long (not 4,6, or 8 like other systems) and that a pointer is invalidated
if "touched" by anything other than a pointer operation (which in turn will
check the users "right" to play in that part of the memory.

If you realy want to understand why you're safe with a 400, check out Frank
Soltis' book.
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