Path: utzoo!attcan!uunet!seismo!sundc!pitstop!sun!burgundy!jborza
From: jborza%burgundy@Sun.COM (Jim_Borza)
Newsgroups: comp.sys.ibm.pc
Subject: Re: RLL Hard Disks
Summary: Not so!
Message-ID: <75473@sun.uucp>
Date: 31 Oct 88 21:22:38 GMT
References: <1541@valhalla.ee.rochester.edu> <584@tank.uchicago.edu>
Sender: news@sun.uucp
Lines: 32

In article <584@tank.uchicago.edu>, ads4@tank.uchicago.edu (adam david sah) writes:
> RLL IS unreliable now. Now only because the new generation of machines has
> higher clock speeds, which exceed the capability of RLL controllers to 
>necessarily encode the data fast enough. One friend of mine had to slow 
>down his AT from 12mhz to 6mhz in order to ensure 100% writing! The results 
>previously were disastrous. If anyone can confirm this, please reply publicly!
> 

I don't think it is RLL which is unreliable.  The existence of an RLL-encoded
disk is not (necessarily) apparent to the CPU except in the increased number
of sectors-per-track.  The type of encoding (MFM or RLL) is only an issue
between the controller and the disk drive.

As with nearly all PC peripherals, some controller cards are more adaptable 
than others, particularly in their ability to run with different bus speeds.
If I were to hazard a guess, I think your friend's problems were caused by
the controller card and its interface with the bus. Some cards provide 
track buffering and other features to improve performance and reliability.
Many are low-cost clones designed for a limited performance range and get
caught up when the user is smarter than they are.

Another problem lies with many (not all) expansion card manufacturers' re-
luctance to distribute specifications and schematics with their hardware.
Bottom line:  RLL is a proven encoding scheme which provides higher den-
sities than MFM with a larger base of drives than many manufacturers are 
willing to admit.  There are many more variables to contend with external
to the encoding scheme in the typical PC/AT system.


Jim Borza
Communication Factors - Fremont, CA (415) 797-3039
Sun Microsystems - Milpitas, CA