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'Multitasking without interrupt (ot re: spooling ex'
1999\05\19@161405 by Graeme Smith

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Your right of course....

Actually I was using the Print Spooler as an example, and it predates DOS
by a wide margin. IBM mainframes used a similar task as did digitals minis
and so on. In fact linux actually creates a "spooler" directory for each
users account.

To point out that in ONE implimentation it uses an interrupt, is to ignore
the fact that in SOME of these implimentations it might not have, and as a
"BACKGROUND" task, it certainly didn't need to, if the system is based on
a cooperative sequencing algorythm.

Interrupts were not all that prevalent in early computers, and I beleieve
that spoolers were found necessary, long before interrupts became derigor.
After all, if you are running a task that takes a long time, you have to
have SOME way of switching back and forth between it and your main tasks.

It is my guess that SPOOLERS PREDATE either dos or interrupts by a WIDE
margin. They are sort of the flip side of POLLING, another technique that
has fallen by the wayside since the implimentation of interrupts.

I hope this clarifies to some extent the nature of the difference between
an algorythm that is "Generally Interrupt driven" and an algorythm that is
"Interrupt dependent".

                               GREY

GRAEME SMITH                         email: spam_OUTgrysmithTakeThisOuTspamfreenet.edmonton.ab.ca
YMCA Edmonton

Address has changed with little warning!
(I moved across the hall! :) )

Email will remain constant... at least for now.


On Mon, 17 May 1999, Dr. Imre Bartfai wrote:

{Quote hidden}

1999\05\19@180821 by William Chops Westfield

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   Actually I was using the Print Spooler as an example, and it predates DOS
   by a wide margin. IBM mainframes used a similar task as did digitals minis
   and so on. In fact linux actually creates a "spooler" directory for each
   users account.

I think you'll find that the original use of "spooling" was to send
printer or cardpunch output to a magtape rather than a physical printer.
Magtape speeds were more matched with CPU speeds, and this avoided having
the ($$$$$$$$) CPU have to sit around and wait for the (slow) printer.
An appropriately equipped printer could print directly from the magtape.
IIRC, "SPOOL" is an acronym, and one of the "O"s is for "offline."

Whether there is a print spooling application on your computer is
completely separate from whether the printer hardware uses interrupts or
not.  Printer interrupts are neither necessary nor sufficient to
implement spooling (in the modern sense of "spooling."

I suspect the original intent was for PC printers to use the interrupt
line, but that there was such variation in the printer-side
implementation of the signal that this proved to be impractical.  You
really do NOT want "interrupt per character" behavior on a high speed
printer (interestingly, some serial UARTS have similar problems -
dispite FIFOs, they end up doing per-character interupts.)  OTHO, some
of the "printer buffers" that go in between your computer and the
printer COULD more easily make good use of interrupts - I don't know
whether any of them do.

BillW

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