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From: davidsen@steinmetz.steinmetz.UUCP (William E. Davidsen Jr)
Newsgroups: comp.sys.att
Subject: Re: 7300 hard drive controller
Message-ID: <6457@steinmetz.steinmetz.UUCP>
Date: Thu, 25-Jun-87 16:09:24 EDT
Article-I.D.: steinmet.6457
Posted: Thu Jun 25 16:09:24 1987
Date-Received: Sat, 27-Jun-87 03:27:47 EDT
References: <117@arnold.UUCP>
Reply-To: davidsen@kbsvax.steinmetz.UUCP (William E. Davidsen Jr)
Organization: General Electric CRD, Schenectady, NY
Lines: 23
Keywords: unixpc disk controller
Summary: buffered seeks


ST506 does unbuffered seeks. The communication between the controller
and the disk is in the form:
  step..done..step..done..step..done

for ST412, the buffered step looks like:
  step..step..step..step..done

The step commands from the controller are saved (buffered) in the disk
electronics, and the drive sends back a done when all step commands are
satisfied.

Some disks take better advantage of buffering than others; a drive may
be conforming and just use a counter, or it may do neat stuff like
accelerate the heads half way to the final destination and brake them
for the remaining half. This is called a "balistic seek" (sp?) and makes
long seeks almost as fast as short seeks.


-- 
	bill davidsen		(wedu@ge-crd.arpa)
  {chinet | philabs | sesimo}!steinmetz!crdos1!davidsen
"Stupidity, like virtue, is its own reward" -me