22 Aug 94, Louis Rizzuto writes to Kelly Schrock:

 > Hi, Kelly.  I don't know OS/2 but it seems to me that denial to write to
 > a exe file might be denied based on not having it set up with proper
 > acess.  Why should OS/2 or any operating system presume what files are
 > writeable or not.  Doesn't seem to make sense to me - unless OS/2 is
 > marking all .exe's as "Read Only" for some inexplicable
reason.  Hmmmm.

OS/2 denies write access to its executables so that it can save memory two
different ways.  First, by guaranteeing that the executable will not change
during the time it is running, it can mark all the pages the executable
resides in as "discardable."  When a page is "swapped
out," it is simply removed from memory and re-loaded from the
executable file when it's needed rather than being moved to the swapfile,
like the program's data is.

Also, by only having one copy of the executable in memory at any given
time. It can only do this if it can guarantee that the applications that
the system intends to run are all identical and it can only guarantee that
if it opens the program in "Deny Read Write" mode.  It doesn't
change the executable to "read only" it merely opens it such that
it can't be shared with any task that might write to it.

It's really not all that tough to understand, is it?

- Jon

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