Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!watmath!clyde!caip!rutgers!lll-crg!lll-lcc!well!ewhac
From: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Newsgroups: net.micro.amiga
Subject: Re: ICON scheme, yucccchh.  yishh.. Bletch.
Message-ID: <1924@well.UUCP>
Date: Mon, 13-Oct-86 04:28:33 EDT
Article-I.D.: well.1924
Posted: Mon Oct 13 04:28:33 1986
Date-Received: Tue, 14-Oct-86 05:02:01 EDT
References: <8610050713.AA13268@cory.Berkeley.EDU> <331@husc6.HARVARD.EDU>
Reply-To: ewhac@well.UUCP (Leo 'Bols Ewhac' Schwab)
Organization: Whole Earth Lectronic Link, Sausalito CA
Lines: 50
Summary: No matter how you slice it, it's still screwey.

In article <331@husc6.HARVARD.EDU> hadeishi@husc4.UUCP (mitsuharu hadeishi) writes:
>	However, some of out comments were taken back to C-A by the
>C-A hackers who had contributed to the discussion, and apparently the
>disk sector allocation scheme was changed in 1.2 to reflect the
>design of Workbench icons.  Apparently if you have a very small file
>the 1.2 allocator attempts to allocate it as close to the home
>directory track as possible.  Space is "reserved" for these small files
>near the home track, or something of this nature.  In any case the
>upshot is because of this icons are displayed MUCH faster under 1.2.
>The Workbench icons seem to come up at least 2 to 3 times faster,
>and if you use AddBuffers they typically come up even more rapidly.
>This new system is totally compatible with 1.1 (since it is just a
>change in the allocator) and yet gives a MUCH more professional
>appearance to icon display for disks written under 1.2.
>
>			-Mitsu

	I wrote a hack some time back called "fm" that gave you a visual
picture of sector allocation of files on the disk (yes, I did throw it at
the net).  Here are some of the observations I've made.

	Under 1.1, data blocks grow downward toward track 0, file info
blocks grow upward.  Data blocks for a given file are kept as close to each
other as practical; file info blocks for a given file are arranged
similarly.  File info and data blocks are rarely near each other.

	Under 1.2, the very first data block is *always* right next to the 
file header block.  This is what makes icons come up so fast under 1.2.
Data blocks subsequent to the first one are allocated as per the 1.1 scheme.
However, this is true for all files, no matter what their size.  So if you
have a lot of 2-block files running around under 1.2, your sector allocation
will look very strange indeed.

	Under both OS's, data blocks grow toward track 0.  Upon getting
there, the allocation algorithm wraps to *TRACK 79!*  So if you've got a
file that spans this boundary, you'll hear, "tic tic tic tic tic
BRRRRAAAAPPP!! tic tic tic..."  This is one of the bigger misfeatures in the
DOS allocation scheme as far as I'm concerned.  It would be "trivial" to
allocate from the center out growing upward once you'd filled the lower half
(wouldn't it?).

	It's also somewhat amusing to observe the effects of fragmentation
after a disk has been used a while, especially for big files.

_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_-_
Leo L. Schwab				ihnp4!ptsfa!well!ewhac
The Guy in The Cape				..or..
					well ---\
"Work FOR?  I don't work FOR		dual ----> !unicom!ewhac
anybody.  I'm just having fun."		hplabs -/       ("AE-wack")