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Inside Macintosh: Devices /

Chapter 3 - SCSI Manager / SCSI Manager Reference

Data Structures

Partition Map Entry Record

The partition map entry record contains information about how data is stored on a block device, usually a SCSI disk drive. The partition map entry record is defined by the Partition data type.

TYPE Partition = 
RECORD
   pmSig:         Integer;       {partition signature}
   pmSigPad:      Integer;       {reserved}
   pmMapBlkCnt:   LongInt;       {number of blocks in partition map}
   pmPyPartStart: LongInt;       {first physical block of partition}
   pmPartBlkCnt:  LongInt;       {number of blocks in partition}
   pmPartName:    PACKED ARRAY [0..31] OF Char; {partition name}
   pmParType:     PACKED ARRAY [0..31] OF Char; {partition type}
   pmLgDataStart: LongInt;       {first logical block of data area}
   pmDataCnt:     LongInt;       {number of blocks in data area}
   pmPartStatus:  LongInt;       {partition status information}
   pmLgBootStart: LongInt;       {first logical block of boot code}
   pmBootSize:    LongInt;       {size of boot code, in bytes}
   pmBootAddr:    LongInt;       {boot code load address}
   pmBootAddr2:   LongInt;       {reserved}
   pmBootEntry:   LongInt;       {boot code entry point}
   pmBootEntry2:  LongInt;       {reserved}
   pmBootCksum:   LongInt;       {boot code checksum}
   pmProcessor:   PACKED ARRAY [0..15] OF Char; {processor type}
   pmPad:         ARRAY [0..187] OF Integer;    {reserved}
END;

Field Description

pmSig

The partition signature. This field should contain the value of the pMapSIG constant ($504D). An earlier but still supported version uses the value $5453.

pmSigPad

Reserved.

pmMapBlkCnt

The size of the partition map, in blocks.

pmPyPartStart

The physical block number of the first block of the partition.

pmPartBlkCnt

The size of the partition, in blocks.

pmPartName

An optional partition name, up to 32 bytes in length. If the string is less than 32 bytes, it must be terminated with the ASCII NUL character (a byte with a value of 0). If the partition name begins with Maci (for Macintosh), the Start Manager will perform checksum verification of the device driver's boot code. Otherwise, this field is ignored.

pmParType

A string that identifies the partition type. Names that begin with Apple_ are reserved for use by Apple Computer, Inc. Names shorter than 32 characters must be terminated with the NUL character. The following standard partition types are defined for the pmParType field:

	String	Meaning
	Apple_partition_map	Partition contains a partition map
	Apple_Driver	Partition contains a device driver
	Apple_Driver43	Partition contains a SCSI Manager 4.3 device driver
	Apple_MFS	Partition uses the original Macintosh File System (64K ROM version)
	Apple_HFS	Partition uses the Hierarchical File System implemented in 128K and later ROM versions
	Apple_Unix_SVR2	Partition uses the Unix file system
	Apple_PRODOS	Partition uses the ProDOS file system
	Apple_Free	Partition is unused
	Apple_Scratch	Partition is empty

pmLgDataStart

The logical block number of the first block containing file system data. This is for use by operating systems, such as A/UX, in which the file system does not begin at logical block 0 of the partition.

pmDataCnt

The size of the file system data area, in blocks. This is used in conjunction with the pmLgDataStart field, for those operating systems in which the file system does not begin at logical block 0 of the partition.

pmPartStatus

Two words of status information about the partition. The low-order byte of the low-order word contains status information used only by the A/UX operating system:

	Bit	Meaning
	0	Set if a valid partition map entry
	1	Set if partition is already allocated; clear if available
	2	Set if partition is in use; may be cleared after a system reset
	3	Set if partition contains valid boot information
	4	Set if partition allows reading
	X	Set if partition allows writing
	6	Set if boot code is position-independent
	7	Unused

The remaining bytes of the pmPartStatus field are reserved.

pmLgBootStart

The logical block number of the first block containing boot code.

pmBootSize

The size of the boot code, in bytes.

pmBootAddr

The memory address where the boot code is to be loaded.

pmBootAddr2

Reserved.

pmBootEntry

The memory address to which the Start Manager will transfer control after loading the boot code into memory.

pmBootEntry2

Reserved.

pmBootCksum

The boot code checksum. The Start Manager can compare this value against the calculated checksum after loading the code.

pmProcessor

An optional string that identifies the type of processor that will execute the boot code. Strings shorter than 16 bytes must be terminated with the ASCII NUL character. The following processor types are defined: 68000, 68020, 68030, and 68040.

pmPad

Reserved.

See "The Structure of Block Devices," beginning on page 3-12, for more information about this data structure.