Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!decwrl!labrea!rutgers!bellcore!tness7!ninja!cpe!neese
From: neese@cpe.UUCP
Newsgroups: comp.unix.xenix
Subject: Re: *nix performance
Message-ID: <6800048@cpe>
Date: 4 Oct 88 13:50:00 GMT
References: <1428@draak.cs.vu.nl>
Lines: 20
Nf-ID: #R:draak.cs.vu.nl:1428:cpe:6800048:000:1063
Nf-From: cpe.UUCP!neese    Oct  4 08:50:00 1988


Another choice is to use an adapter card that assumes bus-mastership.
This allows the CPU the freedom of not having to deal with the DMA
on the AT, which is sloooowww.  This type of arrangement also minumizes
the number of interrupts the CPU has to deal with in terms of disk I/O.
If the DMA on the adapter is fast, then this is a win.
Pile on top of that,....if the adapter is a SCSI implementation, then
you can run multi-threaded I/O, whichs allows multiple commands to be 
issued to the SCSI bus for multiple devices.  This even increases
throughput more and reduces the CPU overhead further.  It does, however,
require an intelligent SCSI Host adapter to accomplish this goal.
In this scenario, commands can be issued to the SCSI bus without worrying
about the bus being busy.  One interrupt covers multiple commands, so the
CPU load is reduced again.
The big caveate; some AT class computers cannot run bus-mastership due
to an incorrect implmentation of the AT bus.

					Roy Neese
					Tandy Computer Product Engineering
					UUCP@ killer!ninja!cpe!neese