khera@thneed.cs.duke.edu (Vick Khera) (11/29/90)
In article <59300@microsoft.UUCP> jimad@microsoft.UUCP (Jim ADCOCK) writes:
Having used both Unix-style huge linear addresses, and Intel 80x86
segments, I believe neither has much in common with OOP. In either
one has to copy objects around, or do manual clustering of objects
via heuristics, etc. Maybe one needs hardware based on an
obid+offset, with automatic support of clustering?
The "huge linear address" of Unix-style machines is a farce in the
first place, given that that "huge linear address" is built of 4K
typical pages, which are mapped in unique ways to disks, and
programmers have to reverse engineer all these aspects to get good
performance in serious applications.
you seem to be implying that a segmented architecture is better than a
system that implements virtual memory in a linear address space.
there is no need to "reverse engineer" all those aspects to get good
performance out of a Unix OS. The OS has the freedom to figure out
which parts of the application are needed and have those in memory,
with the rest loaded in on demand. This also reduces initial startup
time since the whole program doesn't need to be loaded into memory
before it starts to execute. if the program is sufficiently small and
the computer's memory is sufficiently large, the whole program can sit
in memory with no problems or hassles of segments.
i agree that it is beneficial to cluster objects and code that
reference each other in the same pages to reduce the page faulting in
a virtual memory machine. it is not that crucial, however, since we
don't have to worry about crossing segment boundaries and the OS will
figure out which pages it needs (the working set).
segmented architectures are a thing of the past. when DEC went to
create the successor to the PDP line, they started with a segmented
architecture and quickly decided it was a botch. then they came up
with the virtual architecture extension (known today as the VAX). the
only reason Intel sticks with the idea is the amount of investment
they have in it and all those little pee-cee's out there that need
backward software compatibility. though this is an admirable goal,
there comes a point when you just have to cut your losses and go with
a better idea.
v.
--
=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=
Vick Khera, Gradual Student/Systems Guy Department of Computer Science
ARPA: khera@cs.duke.edu Duke University
UUCP: ...!mcnc!duke!khera Durham, NC 27706 (919) 660-6528