Re: base and bounds, Why I've Dropped In

On 6/16/2025 7:37 AM, quadibloc wrote:

On Mon, 16 Jun 2025 4:02:26 +0000, Stephen Fuld wrote:

On 6/15/2025 1:09 PM, MitchAlsup1 wrote:

 

Who was it that said:: The worst error a computer architect
can make is to specify insufficient number of address bits ??
>
Gordon Bell ?
>
Base and bunds simply doubles down on avoiding this rule.

>
I am not sure what you are saying here.  There are different "limits"
involved.  One is the maximum addressable by a single program, another
is the maximum memory the architecture can support, another is the
maximum size of a section.  This last is related to the design of the
ISA, i.e., register size, number of bits used for displacement, etc.
These limits don't have to be the same.

 The first two are the ones that were being considered. If an ISA doesn't
allow you to run big programs on it - the first - and even more so if it
only works on a computer with a small memory, then, when you go out and
get a shiny new computer, it's going to have a different ISA.

Yes.  The first two are not issues related to the choice of base and bounds versus pages.  As I pointed out, and your agree, they are ISA design issues.  Which is why I questioned what Mitch meant.

The second, though, has often been gotten around while retaining
compatibility. If you have base and bounds, the base isn't visible to
the user, so making the base bigger on a newer version of the computer
doesn't break compatibility, except for needing to update the operating
system.

Absolutely.
--
  - Stephen Fuld
(e-mail address disguised to prevent spam)