Path: utzoo!bnr-vpa!bnr-fos!bmers58!atreus!keithh
From: keithh@atreus.uucp (Keith Hanlan)
Newsgroups: comp.sys.amiga
Subject: Questions about Harddisks
Message-ID: <553@bmers58.UUCP>
Date: 27 Nov 89 19:27:08 GMT
Sender: news@bmers58.UUCP
Reply-To: keithh@atreus.UUCP (Keith Hanlan)
Organization: Bell-Northern Research, Ottawa, Canada
Lines: 66

I'm putting together an A2000 machine...

Arggh! I'm going to World of Commodore this weekend with the express 
purpose of getting a controller/memory/harddisk and would appreciate 
some informed opionions about:

o DMA vs non-DMA
	I'm almost ready to give up. I continue to read conflicting
	optinions about DMA vs non-DMA hard-disk controllers. My gut
	opinion is that DMA is a more elegant solution that off-loads the
	CPU and hence doesn't degrade the machine as much. Am I right?
	Then why does anybody build non-DMA? Why do they claim such
	remarkable through-put with some non-DMA drives? And finally,
	what the heck is the "quasi" DMA and "true" DMA I occassionally 
	hear about.

o ST-506 vs SCSI vs ESDI
	These are just low-level protocols right? My perception is that
	ST-506 is what you find in PC's, SCSI is more popular with others,
	and ESDI is for file-servers etc... Does this mean that each is
	"tuned" to a different speed and throughput requirements? Does that
	mean I pay more for SCSI and even more for ESDI? Does that mean each
	will be progressively "faster"?

o importance of access speed 
	That's all a drive manufacturer will give you. Near as I can figure
	it doesn't matter a tinker's cuss what the access speed is within a
	few dozen milli-seconds: it seems to be the controller that really
	matters.

o ways of measuring through-put
	I'm putting together a software development environment. I'm
	interested in a harddisk that will let my compiler really scoot.
	Are there somethings I should be more concerned with? What things
	don't matter as much? Are some controllers more appropriate for this
	kind of work than others?

Dave Haynie (whose opinions I respect) explains that the 
	"main trouble I've seen with the magazine reviews of HD 
	 controllers is that the reviews don't quite understand or 
	 bother to deal with a real, sound, scientifically 
	 accurate comparison. For such a test, you've got to 
	 benchmark each controler with exactly the same hard
	 disk, ..., under a variety of system load conditions."

I'll buy that! As far as my inexperience helps, every review uses a
set of metrics more or less completely orthogonal for every other
review. Yes, sure they may give some of the same measurements but if the
conditions vary, then I don't know how to compensate.

I am leaning to GVP for a couple of reasons:
	o My dealer supports them and speaks very highly of their support
	  *but* I should be able to get support at least as good for 
	  CBM stuff I buy.
	o They have a good upgrade path to an '030/882 and 32bit RAM
	  *but* maybe everybody else '030 boards are compatible with everybody
	  else's drives, controllers, and RAM add-ons.
	o Their market share seems re-assuring
	  *but* advertising is hardly a fair evaluation.

Your opinions and information will be GREATLY appreciated.

Thank you,
Keith Hanlan
Bell-Northern Research
utgpu!bnr-vpa!bnr-fos!bmers58!keithh%atreus or keithh@bnr.ca