Zenith Z-100 Series, Technical Manual

Page: 440 / 493

Page 10.14
Z-DOS INITIALIZATION SEQUENCE
This section describes all phases of Z-DOS initialization from
the time that control is passed from the system ROM until
Z-DOS gives control to COMMAND.COM for standard system
operation. Following the initialization description are some
sample initialization programs.
Z-DOS start-up is basically a two-step process. First, the
loader is loaded from sector zero of the diskette. Then, the
loader loads IO.SYS from the diskette and passes control to
IO.SYS. The IO.SYS:
• Load s the operating system.
• Load s COMMAND.COM.
• Pass e s control to COMMAND.COM.
The following sections thoroughly discuss each of these func-
tions.
The Loader
The purpose of the loader is to load in lO.SYS and pass con-
trol to it. The first 512 bytes of every diskette (or full sector
if sector sizes are greater than 512 bytes) is reserved for the
loader. The loader resides in a known location on the diskette
(the first 512 bytes) so that the system ROM can correctly
locate it when the user issues the BOOT command to the
ROM.
The loader is placed on the diskette by the FORMAT program.
The same loader is used on each type of diskette, whether
it is 8 inch or 5-1/4 inch. A small table located at offset 3
in the loader contains specific information about the type of
diskette that it resides on. This disk information is placed in
the loader by FORMAT just before FORMAT writes the loader
onto a newly formatted diskette.