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From: lbl@druhi.UUCP (LocklearLB)
Newsgroups: net.micro.atari16
Subject: Re: Floppy Disk Speed
Message-ID: <742@druhi.UUCP>
Date: Thu, 24-Jul-86 11:32:43 EDT
Article-I.D.: druhi.742
Posted: Thu Jul 24 11:32:43 1986
Date-Received: Fri, 25-Jul-86 20:56:09 EDT
References: <332@sdcarl.UUCP>
Organization: AT&T Information System Labs, Denver, Co
Lines: 38
Summary: a tip

In article <332@sdcarl.UUCP>, tre@sdcarl.UUCP (Tom Erbe) writes:
> 
> .
> 	The floppy disk on my ST seems to run very slow.  I have seen this on
> other STs, so I think it is a design flaw.  If I am not imagining this, where
> does the fault lie?  Is it the disk, the controller, or the software?  Will 
> there be a fix for this from Atari?  
> -- 
> 	Tom Erbe
> 	Computer Audio Research Lab, UCSD
> 	Q-037
> 	La Jolla, CA  92093
> 	619-452-4384
> 	{ucbvax,ihnp4,akgua,hplabs,sdcsvax}!sdcarl!tre

I have read benchmarks that indicate that the ST floppies are rather slow.
The most likely culprits are GEMDOS and the floppy driver code.  I haven't seen
GEMDOS code ( I certainly would like to!), but I have looked at the driver code.
It really isn't as optimized as it could be.  

In fact it is far too understandable to have been optimized! :) :)

But seriously, while looking at the code I discovered something I would like
to pass on:

If the buffer that is specified in a read or write operation is not on a word
boundary, the resulting operation is going to be VVEERRYY SSLLOOWW!!  The main 
reason for this is that the DMA buffer must be on a word boundary.  If the user
buffer is not on a word boundary, the driver must read a sector at a time into 
its own word aligned buffer and copy it to the user buffer.  If the buffer 
IS word aligned, then it merely DMA's the requested sectors into the user buffer 
straight from the floppy.

Needless to say, the second option is much faster.

Moral:  In your programs, always try to use a word aligned buffer for disk requests.

Barry Locklear