The document defines the kernel as the core of an operating system that provides basic services for I/O. It discusses I/O services provided by the kernel like scheduling, buffering, caching, spooling, device reservation, error handling, and I/O protection. The document also describes data structures like open file tables that the kernel uses to track the state of I/O components and activities.

1. By
Aatiqa Bint e Ghazali(2298-BSSEF13-A)
Jaweria Khalid
(2272-Bssesf13A)

2. Define kernel.
I/O Services provided by kernel.
Data structures in I/O subsystems.
Illustration via diagrams.

3. The essential center of a computer operating
system, the core that provides basic services
for all other parts of the operating system.

4.  Scheduling
 Buffering
 Caching
 Spooling
 Device reservation
 Error handling
 I/O protection

5. It means to determine a good order in which
to execute input/output.
Often called disk scheduling.
Scheduling I/O requests can greatly
improve overall efficiency. Priorities can also
play a part in request scheduling.

7.  store data in memory while transferring
between devices.
 Buffering is done for three reasons :
• To cope with device speed mismatch.
• To cope with device transfer size mismatch.
• To maintain “copy semantics”.

8. Caching involves keeping a copy of data in
faster access location than where the data is
normally stored.
Buffering and caching are very similar,
except that a buffer may hold the only copy
of a given data item, whereas a cache is just
a duplicate copy of some other data stored
elsewhere.
.

9. hold output for a device such as a printer
that cannot accept interleaved data streams.
In a device that can serve one request at
time.

10. provides exclusive access to a device
• System calls for allocation and de-
allocation
• Watch out for deadlock

11. OS can recover from disk read , device
unavailable, transient write(when a buffer
becomes overloaded) failures.
Most return an error number or code when
I/O request fails
System error logs hold problem reports

12.  User process may accidentally or purposefully
attempt to disrupt normal operation via illegal I/O
instructions .
 To prevent user from doing so
• All I/O instructions defined to be privileged
• I/O must be performed via system calls.

14. The kernel needs to keep
state information about the
use of I/O components .
It does so through a variety of
in-kernel data structures such
as open file table .
The kernel uses similar
structures to track network
connections, character-device
communications and other
I/O activities ,