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From: pshuang@ATHENA.MIT.EDU
Newsgroups: comp.sys.ibm.pc.misc
Subject: Hard disk question
Message-ID: <9106042133.AA25173@heath-bar-crunch.MIT.EDU>
Date: 4 Jun 91 21:33:20 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Lines: 40

IBM-PC compatibles can easily handle hard disk with more than 32
megabytes of space.  However, DOS versions before 4.x could not access
more than 32Mb as a single drive letter.  Since DOS is capable of
partitioning a physical hard disk drive unit into multiple drive
letters, this was the most common solution to the 32Mb limit.  Other
solutions include tweaking around with custom versions of DOS (i.e.
Compaq's DOS 3.31) and loading device drivers.  The latter two solutions
are often incompatible with old software.

If you're running DOS 4.x (which you probably are if you bought the
system recently), you need not worry about any of this.  To verify that
you are using all the disk space that you bought, perform a "CHKDSK"
command on your drive and see if the reported total space is about forty
million.  If the reported space is about thirty-two million, try doing a
"DIR D:" and see if you have eight megabytes there.

Microsoft Windows 3.0, when running on a machine with an i386-class CPU
(including the 80386SX) is capable of creating virtual memory out of
your hard disk space.  This means that when it uses up all your real
memory in the machine to load programs and store data, and it needs
more, it can "page" parts of memory which isn't currently being used
out.  Paging is made possible by the i386's hardware support, and
essentially Windows looks at all the stuff it's storing, says to itself
"Gee, I haven't used this piece for a long time" and saves the stuff to
a disk file and frees up the memory previously occupied for other
purposes.  If later the piece that was saved is needed again, Windows
knows to reload it from the disk file.  This process makes it possible
to run programs which require more RAM than you can afford, but since
hard disks are orders of magnitude slower than RAM chips (typically a
million times slower, since access times are milliseconds rather than
nanoseconds), paging takes a heavy toll on performance.

See your Windows manual for more details about swapping (which is what
Microsoft has decided to call this process, instead of paging) and
swapfiles when in Enhanced 386 mode.  If you don't have a manual, (1)
shame on you! (2) try one of the many Windows tutorial books.

Singing off,
UNIX:/etc/ping instantiated (Ping Huang).