From: jnsims01@ulkyvx.louisville.edu
Newsgroups: comp.sys.mac.system
Subject: Re: "Get Info" reports different size when file is moved
Date: 31 Jul 92 14:15:26 GMT
Followup-To: comp.sys.mac.system
Distribution: usa
Organization: University of Louisville

In article <1992Jul30.141956.13014@eplrx7.es.duPont.com>, milbouma@esvax.dnet.
  dupont.com writes:
> This subject has come up before, I think, but I need a refresher, prompted 
> by a question from a curious fellow Mac support person. How does the Finder 
> and Get Info calculate/report the amount of disk used by a document?
> 
> (description of 'The specific situation' deleted to save bandwidth)

Two different numbers are reported by 'Get Info': the number in parentheses
reports the actual number of bytes in the file. You'll notice that this number
doesn't change for a given file no matter where or under what System software
it was stored. The other number, reported in kilobytes, is the amount of disk
storage this file occupies. This will vary depending on the smallest chunk of
disk storage that can be allocated to a given file based on System software
version and media capacity - brief explanation follows.

Any operating system divides a formatted media into some fixed number of chunks
and then keeps track of which file owns which chunk. Each chunk (called
variously blocks, clusters, etc.) can be assigned to only one file at a time:
the operating system determines who wons what by _allocating_ those chunks. 
Assume for a moment that the the file allocation table under System X can keep
track of 100 chunks of data on whatever media you're using. If you have a 400K
floppy, those chunks will each be 4K big, right? If you have a 800K floppy, on
the other hand, each chunk will be 8K big. A 2k file on the smaller floppy will
be 2k big and will consume 4K of space because that's the smallest allocatable 
unit. The same file on the bigger floppy will still be 2k big, but it will 
consume 8K because, again, that's the smallest allocatable unit. (Note that
these figures are only examples; in practise, the actual smallest allocatable
block will vary depending on version of the operating system, type of media,
and a number of other things.)

The ramifications of this are very important: If you have a large capacity
drive, the minimum allocatable block size is likely to be pretty large. This
doesn't really matter if you're only going to store a relatively small number
of files. But if you intend to store lots of small files, you will waste quite
a bit of space because of the difference between the size of your documents and
the smallest allocatable block each one will consume. This is why it can be
very effective to partition your hard drive: this reduces the size of that
minimum allocatable block.

I hope that's clear; if not, send me an e-mail or call and I'll try again. 

 My wife AND my employer ignore my opinions - feel free to do the same!
.......................................................................
: John Norman Sims, Jr.    : Internet: jnsims01@ulkyvx.louisville.edu :
: University of Louisville :     (or)  jnsims01@ulkyvm.louisville.edu : 
: Computing and            :   BITNET: jnsims01@ulkyvm                :
:       Telecommunications : You can't win, you can't break even,     :
: Phone: (502) 588-5565    :       and you can't get out of the game! :
:.....................................................................: