Re: Market pressures for more reliable software

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

Roedy Green <roedy@mindprod.com> writes: > On Wed, 27 Jun 2001 09:41:58 GMT, "Gary Labowitz" <garyl@enter.net>
> wrote or quoted :
> 
> >I'm curious what you mean by "relocation" that you were shocked that S/360
> >didn't have it.
> 
> The univac 1100, the IBM 360s predecessor, had a relocation register
> so you could load a ram image and start executing without having to
> make any adjustments.  
> 
> The 360 used absolute addresses.

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.

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

In the days when the 360 first came out, dynamin program relocation
would have been an advantage (programs were relatively small, say, 200K bytes).
These days the disadvantage of dynamic relocation is that the
time taken to relocate a large program 10Mb, 100Mb becomes significant.

> To load you had to adjust all the
> address references to account for where in RAM the program was loaded.

No, only those words that had been specified as containing an absolute
address.

> This greatly slowed down the process of getting a program started.
> 
> Exploiting relocation hardware to speed loading is still not fully
> exploited even in Windows NT.
> --
> Roedy Green, Canadian Mind Products