Re: RPG400 SDA query?

RE:     Re: RPG400 SDA query?

From: Jon Paris <paris@ca.ibm.com>

>>pointers include permission/access right type information

AKA,   Capability Based Addressing.

John Carr



>>> 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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