Re: S/3xx (was Market pressures for more reliable software)

[robin <robin_v@bigpond.nospam.com>]

"Shmuel (Seymour J.) Metz" <nospam@acm.org> writes: > 
> 
> robin wrote:
> 
> > No. It used relative addressing, and base-relative addressing.
> > (strictly speaking, it used base-displacement-indexed addressing.)
> > The assembler allowed "absolute" addresses to be specified,
> > which had to be filled in by the loader.
> 
> You're confusing two different things.

I'm not confusing anything.

> The S/360 used absolute addresses,

There was only one case when the S/3xx used absolute addressing.
That was when the base register field of an instruction was zero.
The displacement was then effectively the absolute address (in the
range 0-4095).

Remaining addressing mode was base-displacement-indexed addressing,
except for SS instructions, which used base-displacement addressing.

> but they were not present in
> instructions. At least, it did until prefixing came along.
> As to assembler language, it was relocatable addresses
> that had to be adjusted by the loader;

Relocatable addresses are not "adjusted by the loader".
This is done automatically via the base register(s).

> if the program specified
> an absolute address, then the loader did not have
> to adjust it.

When an address constant [A(xxx)] is specified, the loader has to
supply the relevant actual address.  The assembler can only provide
a relative address.

> > Any program can be loaded anywhere in memory.
> > Programs can be made dynamically relocatable, but only with some effort.

> --
> Shmuel (Seymour J.) Metz