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From: krowitz%richter@UMIX.CC.UMICH.EDU (David Krowitz)
Newsgroups: comp.sys.apollo
Subject: Re:  sr9 to sr10
Message-ID: <9003051659.AA24525@richter.mit.edu>
Date: 5 Mar 90 16:59:58 GMT
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SR10 is "Just Like Real Unix" (JLRU) ... all memory space which
is declared by the program is allocated as soon as the program is
started, even if the memory is never actually used during the
execution. Under SR9, memory was allocated in the Aegis style --
ie. memory space was allocated the first time the program actually
uses it during the execution of the program. Since your program never
uses the 1,000,000 4-byte integer array, the SR9 machine never
allocates the disk space needed for the virtual memory of the array.
The SR10 machine allocates the disk space just as soon as the program
is started. This prevents the program from getting part way into its
execution before finding out that the disk is too full for it to 
allocate the memory its needs. The drawback is that the program
always must allocate the full amount of memory even if it is not
going to use it all. It's one of the drawbacks of Unix compatibility.

There is an undocumented and unsupported switch for /com/bind which
causes and SR10 program to use SR9 Aegis style memory allocation. I
believe that it is "-vm_sparse" or "-sparse_vm" or something like
that.


 -- David Krowitz

krowitz@richter.mit.edu   (18.83.0.109)
krowitz%richter.mit.edu@eddie.mit.edu
krowitz%richter.mit.edu@mitvma.bitnet
(in order of decreasing preference)