IBM speed (was Re: Vax 11/780 performance vs Sun 4/280 performance

[ccwilliams at wombat.decnet.uq.oz]

In article <2736 at tekcrl.TEK.COM>, terryl at tekcrl.TEK.COM writes:
> 
> In article <6926 at cit-vax.Caltech.Edu> mangler at 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