From mboxrd@z Thu Jan  1 00:00:00 1970
From: jnc@mercury.lcs.mit.edu (Noel Chiappa)
Date: Sun,  6 May 2018 09:07:38 -0400 (EDT)
Subject: [TUHS] /dev/drum
Message-ID: <20180506130738.E59A618C079@mercury.lcs.mit.edu>

    > 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