HP Vectra Technical Reference Manual page 332

10.6 Boot Process (lNT 19H)
The boot process loads the operating system. The ROM BIOS INT 19H loads the boot sector from
drive /lA:/I or /lC:". This sector must contain the bootstrap loader for the operating system.
Control is then passed to the code loaded from the boot sector. This code is responsible for
loading the operating system. Refer to the appropriate operating system reference
documentation for additional information on its boot process.
10.6.1 Booting From a Flexible Disc
The INT 19H driver attempts to read the boot sector from Drive /lA:" (disc 0). It will retry the read
four times before failing. The boot sector on flexible discs is located on Side 0, Track 0, Sector 1.
Table
1
0.3 contains a description of the contents of a valid boot sector. If drive itA:" contains a
disc that does not have a valid boot sector, then the system will report the error message:
Non-System disc or disc error
Replace and strike any key when ready.
If a valid boot sector is found, it is read into memory starting at location 07COH:0000H (07COOH)
and control is transferred through a FAR JUMP to location 07COH:0000H. It is the responsibility
of this code to load the rest of the operating system into memory.
10.6.2 Booting From a Hard Disc
If the flexible disc drive does not contain a disc, the system will attempt to boot from the hard
disc. Booting from a hard disc is a two step process. First, the active partition must be
determined, then the boot record is read from the active partition.
The hard disc can be divided into as many as four partitions. Each partition contains an operating
system, programs, and data. Only one of the partitions can be active at any time. Partitions are
added, deleted, activated, and deactivated using utilities provided with the respective operating
systems. Partitions occupy a specified number of cylinders on the disc. For example, the optional
20 MB hard disc drive has 606 cylinders. One partition might occupy cylinders 0 through 303,
while the second partition occupied cylinders 304 through 605.
System Processes 323