Legacy Document

Inside Macintosh: Operating System Utilities /

Chapter 9 - Start Manager / Start Manager Reference

Routines / Identifying and Setting the Default Operating System

SetOSDefault

You can use the SetOSDefault procedure to set a byte in parameter RAM that indicates the operating system that gets booted on the Macintosh computer.

PROCEDURE SetOSDefault (paramBlock: DefOSPtr);

paramBlock

A pointer to a default operating system parameter block.

-->	sdReserved	SignedByte	Reserved.
-->	sdOSType	SignedByte	Operating-system type.

DESCRIPTION

The SetOSDefault procedure sets a byte in parameter RAM that indicates the operating system that gets booted on the Macintosh computer. Setting a value of 1 in the sdOSType field indicates the Macintosh Operating System, which is currently the only default operating system allowed. The numbers 0 through 15 are reserved by Apple Computer.

Unless the value in the sdOSType field matches the value in one of the ddType fields of the driver descriptor record, the computer cannot continue booting. Every drive connected to the computer has a driver descriptor record at the beginning of physical block 0.

ASSEMBLY LANGUAGE INFORMATION

The registers on entry and exit for this routine are

Registers on entry
A0	Address of the parameter block for the default operating system record

Registers on exit
A0	Address of the parameter block for the default operating system record

SEE ALSO

For information about the driver descriptor record, see the chapter "SCSI Manager" in Inside Macintosh: Devices.