ZiLOG Z80-RIO Operating System User's Manual page 189

7.3 SOFTWARE ORGANIZATION
The Disk File System driver is divided into two parts to
correspond to the division of the hardware interface.
One part is resident on the host system and contains the
message interface link to communicate with the controller.
It is used to pass I/O requests to the controller and
to send and receive data.
The second, and larger part, is th~ software which
resides in the memory of the intelligent controller.
Most of this is loaded from the disk whenever the
controller is reset. The software in ROM includes the
initial start-up and serial message interface logic,
the bare disk controller, which gives access to the
disk by sector number for reads and writes, and the
self-bootstrapping logic to read the rest of the file
system from the disk. The disk file system, which
is an adaptation of the ZOOS-II file system, and an
interface for handling the request vector across the
remote serial interface, are loaded from the disk.
There are two entry points to the resident software,
each of which takes a standard I/O vector. One, DFS,
causes the vector to be taken as a request to the Disk
File System on the controller, and the other, DISK
(located at address of DFS + 2), causes it to be
taken as a request to the bare disk controller.
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