Re: Arbitrary Sandbox

[tmoran@acm.org]

> An array of a million Booleans contains a million objects, in
> the Ada sense.
    In a segment based architecture that would be one segment. The
array is the object at that level, not the bit.  If you pass that
array as a procedure argument, you mention one name, not a million.

> >...But segments shrink *code* size by
> > occasionally loading segment registers, but usually using a small number
> > of bits to indicate which segment register to use in an operation.
>
> If I understand what you mean, it seems to me you can use a small
> number of bits to indicate which register points to the beginning
> of an array in a flat address space, just as well.
    Yes, you can partially simulate segmented addresses that way.  But
using general registers, rather than specific registers, means the
hardware can't help.  If they are hardware segment registers they can
have security/usage/paging bits and the OS can tell which segments are
in use when it wants to swap something, for instance.
  If you want to code at the bit level in asm or C, then certainly having
every bit equal, with the individual programmer deciding what every bit
means, is appropriate.  If you want to code at a higher level, with things
like "this is an array segment, it's currently located in RAM starting
here, its size is xxx, it's read-only, non-executable", then I prefer
segments.