The Boot Manager architecture distinguishes between system-independent and system-dependent components as part of the startup process of an operating system. The system-independent components are used to connect the POST code sequence executed on a PS/2 or compatible machine to a system selection sequence supplied as part of Boot Manager, which then chains to the operating system-dependent initialization sequence. The system-independent components are:
When Boot Manager is enabled as a startable primary partition, the MBR boots it first, like traditional MBR environments. The MBB manages the remainder of the boot process.
The layers of system independent and system dependent code on the physical disk drive are shown in Figure "Hard Disk Layout".
The MBB is installed in a 1MB primary partition which must be created at the request of the user, by installing Boot Manager. This space is allocated on request by OS/2 Version 2.0's FDISK/FDISKPM utilities and can be created at any location on the disk after track zero. It uses one of the four available primary partitions on the first physical disk.
The MBB contains code that:
The operating system dependent code resides within the logical drives assigned to each operating system. Upon selection of a specific system to be started, this system specific code is executed, loading the chosen operating system.
The logical drives are allocated using the FDISK/FDISKPM utilities provided with OS/2 Version 2.0. These tools update the MBR to indicate which areas on the physical disk have been defined as logical drives containing the operating systems. Boot Manager logical drives can be defined on any ST-506, ESDI or SCSI interface fixed disk drive which is accessed through INT 13h. This precludes logical drives from being created on SCSI devices which are accessed through INT 4Bh; for example, logical drives may not be created on removable media devices.
Once one or more physical drives are set up and logical drives created, the specific operating system's formatting utility is used to supply the operating system boot record within the logical drive. It is important to note that the OS/2 Dual Boot function operates with the system-dependent boot code. Boot Manager neither enhances nor disables the Dual Boot function, since Boot Manager does not affect the contents of any logical drive. Therefore, Dual Boot will work in conjunction with and independent of Boot Manager.
No operating system may store its own information in the MBB or MBR. Any such information must be held within the logical disks owned by that operating system. Operating systems which do not obey this rule will not function correctly in the Boot Manager environment nor in any other "multi-boot" environment, and may compromise disk integrity. Operating systems which are known to obey this rule, and operate correctly in the Boot Manager environment, include: