Inside -, Volume V

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IPR2017-01467 UNIFIED 1023 • APPLE COMPUTER, INC. Copyright © 1988 by Apple Computer, Inc. .Allrights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, ?':lOtocopying, recording, or otherwise, without prior written permission of Apple Computer, Inc. Printed in the United States of America. Apple, the Apple logo, AppleTalk, ImageWriter, LaserWriter, MacDraw, and MacPaint are registered trademarks of Apple Computer, Inc. .-\ppleColor, Apple Desktop Bus, Apple IIGS, A/UX, , Macintosh, MultiFinder, and Switcher are trademarks of Apple Computer, Inc. ColorSet and ImageSet are Trademarks of lmageSet Corpororation. Helvetica and Times are registered trademarks of Linotype Co. is a registered trademark ofMicrosoft Corporation. Modern Artist is a trademark of Computer Friends, Inc. ~uBus is a trademark ofTexas Instruments. POSTSCRIPT is a trademark of Adobe Systems Incorporated. is a registered trademark of AT&T Information Systems. Simultaneously published in the United States and Canada. ISBN 0-201-17719-6 CDEFGIDJ-MU-898 ThirdPrinting, May1988 The SCSI Manager

sbSig (word) always $4552

sbBlockSize (word) block size of dev ice

sbBlkCount (l ong word) number of blocks on device

sbDevType (word) used internally

sbDevID (word) used internal ly

sbData (long word) used internall y

sbDrvrCount (word) number of dr iver descr iptors

ddBlock (long word) f irst block of driver f irst dr iver ddSize (word) dr iver size in bl ocks descr iptor ddType (word) system type (1 for Maci ntosh)

Figure 1. Driver Descriptor Map

SBSig contains the signature; it 's used to verify that the block is valid (that is, the disk has been formatted) and should always be $4552.

SBDrvrCount specifies the number of drivers that may be used for this disk; more than one driver may be needed when multiple operating systems or processors are supported.

There must be a driver descriptor for each driver on the device (as well as a partition map entry , as explained below). DDBlock is the address of the first physical block of the driver code. DDSize contains the size of the driver in blocks. DDType identifies the or processor supported by the driver. The Macintosh Operating System has the value 1; values 0 through 15 are reserved for use by Apple.

To specify a particular operating system for use at system startup, you'll need to call the Start Manager routine SetOSDefault using the same value in ddType (see the Start Manager chapter in this volume).

Partition Map

For the purposes of this discu ssion , a partition is simply a series of blocks that have been alloca ted to a particular operating system, file system, or device driver. (Another way to look at it is that a single physical disk is divided into a number of logical disks.) The partition map organizes, or maps, this allocation of the physical blocks of a disk. It is strongly recommended that all operating systems that run on the Macintosh II use and support the partition map presented here. This will ensure the peaceful coexistence and

Disk Partitioning V-577 Inside Macintosh operation of different operating systems on a single disk, and will enable the transfer of files between partitions.

To support the variety of disk types and sizes that can be attached to the Macintosh II, you should either allow for a variable number of partitions (to be determined at disk initialization), or allocate a large number (greater than 1(0) offixed partition slots.

With the exception of physical block zero, every block on a disk must be accounted for as belonging to a partition.

The partition map contains a number of physical blocks (as mentioned above, the old device partition map, located at physical block 1, has become logical block 0 of the partition map). For each partition on a disk, the partition map has one block that describes the partition. The partition map is itself a partition and contains a partition map entry describing itself. Figure 2 gives an example of a partitioned disk.

dri ver descriptor map partition map entry (driver) partition map entry (A/UX) partition map entry (partition map) part it ion map part it ion < > part it ion map entry (Mac OS)

A/UX part it ion

Mac OS partition

< other part itions >

driver partit ion <

Figure 2. An Example of Disk Partitioning

V-578 Disk Partitioning