HP Vectra Technical Reference Manual page 249

8.1.2 Flexible Disc Drive Support
The disc driver provides support for both standard and high capacity flexible disc drives. The disc
driver supports dual format operation (i.e. reading and writing both types of flexible discs) in the
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high capacity disc drive(s). The flexible disc drives are supported with six functions that perform
read, write, verify, reset, format, and return status tasks.
8.1.3 Hard Disc Drive Support
The system can be configured with an optional hard disc drive. When an internal hard disc drive
is added to the system, the disc driver is "expanded" to include the functions contained in the
BIOS code on the hard disc adapter card.
The hard disc BIOS is integrated into the system during the system generation process (SYSGEN).
Early in the SYSGEN process the software interrupt vector INT 13H is initialized to point to the
flexible disc driver code module. Later in the SYSGEN process the address space between
OC8000H and ODFFFFH is searched for option ROM modules. This search is explained in greater
detail in Section 10. SYSGEN detects the hard disc option ROM and calls it to initialize. During
this initialization process the hard disc driver links into the INT 13H disc driver chain. This process
is explained in greater detail later in this section.
When an INT 13H is executed the hard disc code is called first. The hard disc code checks the
physical drive number specified. If it is a hard disc drive number (greater than or equal to 80H)
the function is executed by the hard disc driver code module. If the physical drive number
indicates a flexible disc drive (less than 80H), the hard disc code module passes control to the
flexible disc driver code module by executing an INT 40H.
8.1.4 External Disc Drives
External disc drives can easily be added to the system. There are two methods for doing this. The
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external disc can supply BIOS code in an option ROM and enter the system in a manner similar to
the internal hard disc. As an alternative, the system could use a DOS installable device driver.
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