Table of Contents
I/O System
PROCESS
Stack
Memory
Management
Disc
I/O
SYSTEM
A
3
FILE
SYSTEM
BUFFER 0
BUFFER 1
File
Request
SOFTWARE
HARDWARE
Figure 7-2.
File System Basic Operation
be allocated for that file.
However, you cannot access the buf-
fers directly;
only by naming records
within files.)
The file
system
can now complete the request by reading the requested re-
cord to the stack.
Note that in none of the preceding operations
did the user process specify a device.
An actual
I/O operation
mayor
may not have occurred and the user is
completely unaware
of such
an occurrence.
The operating system,
however,
allows
devices to
be specified
either by
class name or by
a specific
logical device number.
This permits,
for example,
inputting or
outputting files
via a specific terminal,
card reader,
or line
printer.
7-3. DEFINITION OF TERMS
As shown in figure 7-3,
a Device Controller in the I/O system is
the hardware
I/O
linkage between
the CPU and
I/O device.
It
typically
consists of
one or
more
logic cards.
Depending on
particular controllers,
the Device Controller may drive only one
peripheral (such as a card reader)
or may be capable of
driving
several peripherals (such as disc units).
Figure 7-3 illustrates
7-3
Chapters
Table of Contents
Troubleshooting
