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From: keith@apple.UUCP (Keith Rollin)
Newsgroups: comp.sys.mac
Subject: Re: A Rather dumb question...
Message-ID: <6721@apple.UUCP>
Date: Thu, 12-Nov-87 12:37:58 EST
Article-I.D.: apple.6721
Posted: Thu Nov 12 12:37:58 1987
Date-Received: Sat, 14-Nov-87 19:30:46 EST
References: <1939@crash.CTS.COM> <1720@cognos.UUCP>
Reply-To: keith@apple.UUCP (Keith Rollin)
Organization: Apple Computer Inc., Cupertino, USA
Lines: 39

In article <1720@cognos.UUCP> roberts@cognos.UUCP (Robert Stanley) writes:
>In article <1939@crash.CTS.COM> maddie@pnet01.UUCP writes:
>
>>  Anyone out there know what the maximum Hard-Disk size is on the Mac before
>>you have to partition? For some reason 4 gigabytes seems to pop into my head,
>>can anyone tell me for certain?
>
>I don't know the real answer, because I can't afford individual disks in the
>gigabyte range :-).  However, 4 gig is 2^^32, or the largest binary integer
>value (unsigned), that can be stored in a 32-bit field.  For a variety of
>reasons it is moderately unlikely that a larger field will be used, nor is it
>likely to matter in the reasonable future.  The question is, might it be a
>smaller field?  At present, the Mac could reasonably be described as having a
>24-bit architecture, at least with respect to operating system stuff.  So
>saying, the lower limit would be 2^^24, or 16 meg, but we can readily see that
>the actual limit is greater than this.  Who among us remembers when the
>industry standard high-end disk was 29.5 Meg?
>
>So saying, chances are good that a 32-bit field controls the number in
>question, which gives 4G (unsigned) or 2G (signed).  I know, who would ever
>want a signed value for maximum disk capacity, but stranger things can be
>observed in any operating system...
>

Actually, I think that the maximum FILE size is set at 2G, cause it treats
the long word that holds its size as signed. Don't ask me why, that just
what I heard. However, I haven't had a chance to try it out :-)

When I first saw this question, I responded that I thought the the upper
limit of a hard disk was something like a longword number of 32Meg segments.
Well, that may be technically correct, but is realistically unfeasible.

As I glean it from IM, there is a maximum of 65535 "Allocation Blocks" on
a Macintosh volume. With 512 byte blocks, this leaves you at 32M. However,
each allocation block can be a variable length, as long as it's a
multiple of 512 bytes. This size is refered to as the allocation block
size, and is stored as a long word. So, while you may be able to have a
drive with a 2^17 Terrabyte capacity (I think that's what it comes to),
the minimum size of any files would be 4 gigabytes!