[ih] vm vs. memory

[Brian E Carpenter]

On 25/10/2017 01:12, Paul Vixie wrote:
> 
> 
> Joe Touch wrote:
> ...
>> IMO, they’re no more a stop-gap to networking than VM is to memory.
>>
>> But we’re digressing from the original thread...
> 
> that's hard to say, but i've forked the thread anyway.
> 
> vm is an example of something that started as a workaround but 

I disagree with that evaluation. It started in practice with the
famous "one-level storage system" paper from Manchester**, with the
specific goal of making a small high-speed memory look like a much
larger one. I don't think it was viewed as a work-around, but rather
as a brilliant engineering solution to the high cost of high-speed
memory, vastly easier to use than explicit overlays.

**One-Level Storage System, T. Kilburn, D. B. G. Edwards, M. J. Lanigan, F. H. Sumner, IRE Trans. Electronic Computers EC11(2), April 1962, 223-235.

Full disclosure: I am biased. Frank Sumner was my M.Sc. supervisor.

   Brian

> introduced us to a whole different way of thinking about memory. we now 
> have systems in production that always have physical RAM enough for 
> their work load, and who have no backing store for RAM (paging or 
> swapping) but which still depend on virtual memory for other reasons:
> 
> 1. linear address space; all processes think they have addresses 
> starting from 0.
> 
> 2. page-level protection; various parts of memory are only readable, or 
> writable, or executable, when needed, and at certain privilege levels.
> 
> 3. occasional sharing and/or persistence (memory mapped files).
> 
> 4. occasional distributed persistence (networked virtual memory).
> 
> i think a lot of things that begin as stop-gaps turn out to have many 
> purposes beyond that initial stopped gap, and would have been invented 
> anyway, if somewhat later, for those other reasons.
> 
> LISP may be an example. NAT certainly is.
> 
> i mention this because not all ideas which were terrible $originally 
> remain terrible in $internet_history.
>