Path: utzoo!mnetor!uunet!husc6!hao!ames!ptsfa!hoptoad!unisoft!gethen!bdt!david
From: david@bdt.UUCP (David Beckemeyer)
Newsgroups: comp.sys.atari.st
Subject: Re: A decent disk cache...
Message-ID: <145@bdt.UUCP>
Date: 22 Feb 88 18:10:44 GMT
References: <8802151756.AA02796@ucbvax.Berkeley.EDU> <3293@cup.portal.com> <9232@prls.UUCP>
Reply-To: david@bdt.UUCP (David Beckemeyer)
Organization: Beckemeyer Development Tools, Oakland, CA
Lines: 46
Keywords: Beckemeyers Hard Disk Accelerator

In article <9232@prls.UUCP> gert@prls.UUCP (Gert Slavenburg) writes:
>>  ... but Beckemeyers hard disk accelerator seems to do a good job too ...
>
>Can anybody that uses the hard disk accelerator (or the author) give us some
>more information on what it does, especially :
>
>  1) Does it speed up reading solely (i.e. is it a 'write through' cache) ?
Yes, it is 'write-through' cache.  It doesn't always write-thru actually, but
it *never* buffers the writes for later (i.e. it always physically writes
to the disk).  It attempts to make an intelligent decision about when to
write-thru the cache (which costs the extra memory move), and when to simply
dump the buffer.

HD accel. is a "priority" LRU cache.  The criteria that establishes
"priority" are:
	a) is it FAT info?
	b) is it directory info?
	c) is it "a long way from the last head pos."
Hd accel's main goal is to reduce those long seeks which are slow.  Caching
data on the ST is not as important becuase in fact the DMA rate for large
data xfers is *faster* than a CPU block move.   What costs is moving the
disk heads.  That's why FAT and directory info has priority over data.
>
>  2) Does it solve the TEDIOUSLY SLOW writing problem on not too empty
>     partitions ?
Becuase HD accel. is write-thru, one might think that it is no help to
writing files.  But this is not true becuase TOS has to do a lot of reads
of FATs and dir. info to write to a file.  HD accel doesn't help a lot
with the slow FAT searches, becuase this is more CPU bound with TOS, but
it does help with writing.
>
>  3) Does it solve the 40 folder bug ?  AND/OR
No.  It makes no attempt at this.
>
>  4) Does it work correctly with FOLDRxxx.PRG ?
As far as we know, it works fine.  If there are any problems, they have not
been reported to us.  There have been very few compatibility problems with
HD accel. since Fall '86.  The only known problem is with the new ICD disks
(a bug in the ICD drivers).


-- 
David Beckemeyer			| "To understand ranch lingo all yuh
Beckemeyer Development Tools		| have to do is to know in advance what
478 Santa Clara Ave, Oakland, CA 94610	| the other feller means an' then pay
UUCP: ...!ihnp4!hoptoad!bdt!david 	| no attention to what he says"