6 May
2018
6 May
'18
3:07 p.m.
From: Johnny Billquist
> "A logical segment is a piece of contiguous
memory, 32 to 32K 16-bit
> words long [which can grow in increments of 32 words]"
But then it is not actually giving programs direct
access and
manipulation of the hardware. It is a software construct and service
offered by the OS, and the OS might fiddly around with various hardware
to give this service.
I don't understand how this is significant: most time-sharing OS's don't
give
the users access to the memory management control hardware?
So the hardware is totally invisible after all.
Not quite - the semantics available for - and _visible_ to - the user are
constrained by the mechanisms of the underlying hardware.
Consider a machine with a KT11-B - it could not provide support for very small
segments, or be able to adjust the segment size with such small quanta. On the
other side, the KT11-B could support starting a 'software segment' at any
512-byte boundary in the virtual address space, unlike the KT11-C which only
supports 8KB boundaries.
Noel