Path: utzoo!attcan!uunet!munnari!otc!uqcspe!bunyip!wombat!ccwilliams
From: ccwilliams@wombat.decnet.uq.oz
Newsgroups: comp.unix.wizards
Subject: IBM speed (was Re: Vax 11/780 performance vs Sun 4/280 performance
Message-ID: <118@wombat.decnet.uq.oz>
Date: 30 Jun 88 12:27:40 GMT
References: <22957@bu-cs.BU.EDU> <14968@brl-adm.ARPA> <601@modular.UUCP> <7331@swan.ulowell.edu> <2282@rpp386.UUCP> <6926@cit-vax.Caltech.Edu> <2736@tekcrl.TEK.COM>
Organization: Prentice Computer Centre, Uni. Queensland, Australia
Lines: 28

In article <2736@tekcrl.TEK.COM>, terryl@tekcrl.TEK.COM writes:
> 
> In article <6926@cit-vax.Caltech.Edu> mangler@cit-vax.Caltech.Edu (Don Speck) writes:
>
>>A 2-MIPS CPU would be inadequate to run a BSD filesystem at those speeds,
>>so obviously their software overhead is a lot lower, while at the same
>>time wasting no disk time.  What is VM doing efficiently that Unix does
>>inefficiently?
>  [...]
>      Well, it might be partially due to hardware. Remember the dedicated
> I/O channels the 360-370 systems have??? Do the 4341's have anything
> similar???? Similar to CDC Cyber's peripheral(sp?) processors.
> [...]
> mation before we can say anything. What's the layout of the file on the
> disk??? What type of file is it??? Is it extent-based, or something
> different. If it's extent-based, what are the sizes of the extents???
> Is there really a file system on the disk in question, or is it just that
> one file???? etc.....

	That final point is a telling one. VM file systems are allocated in a
rather primitive way. Each virtual machine/account is allocated disk in 
hard cylinders! yep. If you get an account on one of those machines, your
disk quota will be in a multiple of one cylinder, and your cylinder will be
yours forever. Unix might be a bit faster if each user had his/her own 
one-cylinder filesystem. It usually means there ain't nearly as much track-
track seeking.

Mark Williams