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From: heins@isucs1.UUCP
Newsgroups: net.micro.apple
Subject: Re: Just 1 bit
Message-ID: <14200016@isucs1.UUCP>
Date: Wed, 23-Jul-86 03:34:00 EDT
Article-I.D.: isucs1.14200016
Posted: Wed Jul 23 03:34:00 1986
Date-Received: Fri, 25-Jul-86 00:11:41 EDT
References: <237@ndsuvax.UUCP>
Lines: 20
Nf-ID: #R:ndsuvax.UUCP:-23700:isucs1.UUCP:14200016:000:912
Nf-From: isucs1.UUCP!heins    Jul 23 02:34:00 1986



To read just one bit, you'll have to read a whole sector (using DOS 3.3)
or a whole block (using ProDOS), and then extract the byte which contains
the bit you're looking for, and then use AND with the right mask to
mask out the other 7 bits in the byte, and a CMP to tell if its on or
off... or you could look in either "Beneath Apple DOS", or "Beneath
Apple ProDOS" both are by Peter Lechner and Don Worth and published by
Quality software.  They detail the inner workings of their respective
DOSes, including GCR, and how bits are written and read from the disk.

				Lee Heins
				{umn-cs, okstate, csu-cs}!isucs1!heins
				heins@iowa-state.CSNET

Note: I have no affiliation with Quality software except that I am a
satisfied owner of both of the books mentioned.

Disclaimer: My opinions are in no way the official opinions of Iowa State
University, and any resemblance thereof is purely coincidental...