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From: urlichs@smurf.ira.uka.de
Newsgroups: comp.sys.mac,comp.sys.mac.hardware
Subject: Re: A question about hard disks (300 megabytes or so)...
Message-ID: <1385@smurf.ira.uka.de>
Date: 13 Jan 90 21:37:42 GMT
References: <37739@apple.Apple.COM>
Reply-To: urlichs@smurf.ira.uka.de (Matthias Urlichs)
Followup-To: comp.sys.mac
Organization: University of Karlsruhe, FRG
Lines: 40

In comp.sys.mac.hardware baum@apple.UUCP (Allen Baum) writes:
< []
< >jtn@zodiac.ADS.COM (John Nelson) writes:
< > 
< >>Are there any probl;ems with connecting 300 megabyte disks (.vis. 345
< >>Maxtor or Imprimis/Wren) to the Macintosh?  Can the Finder actually
< >>handle that much space?
< 
< Well, the finder seems to have a limit of 32k? blocks. So, if you have a
< drive over 60M, your blocksize increases, and you get fragmentation. I think.

That's not the finder, that's HFS.
The number of allocation blocks is an unsigned integer, and thus it's limited
to 65535 blocks. If it gets bigger, the block size is increased (in units of
512 Bytes). So any HFS volume up to 32 MB will have 512-byte blocks, up to 64
MB, 1024-byte blocks, then 1536, then ... you get the idea.

There are two problems with this:
o  you'll lose unused space at the end of files (in a sense, that's the
   opposite of fragmentation). So if a file is one byte long, you still need
   2048 bytes to store it, or however big your allocation block size is.
o  you can't have more than 65500 files (although file and directory IDs (file
   IDs don't officially exist yet, but HFS has them anyway) are long integers)
   and
o  the finder calculates needed space for the _source_ volume while copying.
   So if you have 800 small files which you want to copy to a floppy disk, and
   your hard disk is 200 MBytes big (my CDC was 650 MBytes ;-) -- now it's
   only 150, the rest is A/UX stuff), Finder will tell you there's not enough
   space on the floppy, while if you copy them in four installments, well,
   there suddenly is.  This is a Finder glitch which Apple should remove
   someday.
The HFS limitation on 65535 allocation blocks should also be removed someday,
but I doubt that this will happen with Sys 7.0.

Disclaimer: There is a certain operating system which effectively forces you to
reformat your hard disk whenever you want to upgrade to the next version.
It's called "MS-DOS".
Fortunately, whoever designed HFS showed some signs of intelligence.
-- 
Matthias Urlichs