Path: utzoo!mnetor!uunet!husc6!hao!oddjob!gargoyle!ihnp4!cbosgd!osu-cis!tut!erd
From: erd@tut.cis.ohio-state.edu (Ethan R. Dicks)
Newsgroups: comp.sys.amiga
Subject: Re: Amiga 2000 HD Situation
Message-ID: <3119@tut.cis.ohio-state.edu>
Date: 11 Dec 87 16:58:04 GMT
References: <2855@sdsu.UUCP>
Organization: The Ohio State University Dept of Computer and Information Science
Lines: 85
Keywords: hard disks spam

In article <2855@sdsu.UUCP> uzun@sdsu.UUCP (william uzun) writes:
>
>         
[stuff deleted about CA2090 and drive ]
>a 30M drive with controller which Abels will sell for $675.00.  It has
>a 65 msec access time (pretty slow) but the controller is what got to me!
>formats the disk with a 1:1 sector interleave (versus about 3:1 with current
>software and 2090) which means the files are stored as phyically contiguous
>sectors for increased speed, It buffers full tracks (a great trick since it
>is often just as fast to read a track as it is a single sector) and stores
>data in RLL format (for about 3Xs the data per sector almost tripling the
>effective Xfer rate).  The tech I talked too said they intend to support
>auto boot as well! 

Well, well, well... where should I begin...


Sector interleave can be a good thing.  Sector interleave is also largely
transparent.  With a 3:1 interleave, _logical_ sectors are spaced every three
_physical_ sectors.  According to the information sheets posted in the net for
the WEDGE, the Amiga sends requests about every 65ms.  If you do not support
interleaved sectors, the disk will have moved the next sector away from your
heads and you will have to wait for a full revolution to get that sector again.
If you buffer entire tracks (altogether too good of an idea ;-), interleave
is _not_ useful, because, with a standard algorithm, the disk must spin three
times to get a track (assuming you want the entire track).  Track cacheing
is a good thing, IF you have gobs of memory to use up.  As for RLL format, it
does change the rate at which the data are clocked throught the HEAD of the
disk (more bits on the track, same disk speed...).  There is still the
bandwidth of the bus sequence to deal with.  It my understanding that Supra
drives are nonDMA.  This would explain their techniques: if you have a nonDMA
drive which accesses sectors, by the time you pump a sector into the machine,
the disk has spun 1/4 the way around (or more :-) and you must support a
large interleave.  If you buffer entire tracks at a time (in the drive
controller, I hope), then the latency time goes away.  If you have buffering
for multiple tracks, say 10, then you should not experience head slamming
when two tasks are both requesting disk access.  A good controller should
be DMA _and_ buffer several tracks at once, with a good cacheing algorithm (
hmm... how 'bout that dusty PeeCee over there in the corner?).

The other issue is autoboot.  Just _how_ are they going to support autoboot?
Are they going to make you inert their ROMs for CAs ROMs?  Are they going to
patch KickStart?  If you are going to use a KickStart patch, why not just
use a KickBench disk, with about 4 commands in the startup-sequence?  Once
we get KS1.2, after the initial boot when KS1.2 is read in, one never need put
a bootable floppy in the machine..._after the initial boot_.  If we need one
floppy boot anyway (something I personally do NOT mind), why contort the
system.  If you have a KS-in-ROM machine, you need to do a floppy boot anyway
to take advantage of KS1.2.1, and you are in the same boat.  With an actual
ROM patch, you would need to make the harddisk a KickBench, or be in the same
boat as the rest of us: inserting a floppy for some part of the boot process.
How many of you have ever booted a large machine where the bootstrap was on
some other medium (floppy, cassette, PAPERTAPE)?  The idea of booting a
machine from some form of removable medium is not a strange idea (although
it is not always the best idea when you have turnips operating the computer;
the IBM PeeCee would never have gotten anywhere with a boot floppy...too many
turnips use PeeCees at the office every day).


I realize that for many users, hard drives are a black box which sits on the
side (or in the side) of the machine and is supposed to solve all the
problems of the user, but do it _RIGHT NOW, FASTER, FASTER, FASTER_.  When
us humble user types finally get WB1.3, I think we will all notice a much
faster response (like 2X-3X) from our hard drives and a similar response from
our floppies (no, not inside information, just assumptions based on public
knowledge).  It will be at this point that the users will be able to tell
the difference in speed between a DMA drive and a nonDMA drive. Right now,
nonDMA drives are MUCH MUCH cheaper ($300+).  My bets are with the WEDGE, but
I cannot really say, since I have not tested it yet.  IMHO, the WEDGE is faster
than some, and cheaper than ALL harddrives (if you assemble it yourself ;-).  I
will indeed post a review once mine is up and running.

Sorry to be so long winded, but I think that there are too many misconceived
notions about hard disks.

-ethan




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