This document provides an overview of an Operating Systems I course, including course details, textbooks, prerequisites, grading, and an overview of computer system concepts. The computer system concepts section covers processors, memory, I/O devices, registers, instruction execution, interrupts, and the interrupt cycle. It describes the basic components and functions of an operating system at a high level.

1. Faculty of Computers and
Information
Second Year (Second Semester)
Operating Systems I
Dr. Ashraf Elsisi

2. Textbooks
- Operating Systems – Internals And Design
7thPrinciples – Edition
8th- Operating system concepts
-Windows® 7 Resource Kit
-Galvin
-Windows-powershell-cookbook-the-complete-
guide-to-scripting-microsofts-command-shell
Additional Reading:
Tanenbaum - Modern Operating Systems
………

3. Course Description
The purpose of the course is to understand the
general concepts of operating systems.
The course introduces :
•Computer
•Operating
System,
System (Process, Threads,
Concurrency, scheduling,
Memory Management)
If we have time, Deadlock

4. Prerequisites
Introductory course in Theory of systems, Programming
skills, Logic Systems, Computer Architecture, …
Homework + Lab
Homework will be assigned weekly.
Note late homework will not be accepted.
Examination
At least one-hour midterm exam is tentatively scheduled for
week seven of the quarter. The actual data for the exam will be
determined by the progress in the course.

5. Grading
• The composition of the final grade is:
• Homework + Lab + Midterm Exam 40%
• Final Exam 60%

6. Computer System Overview
CHAPTER 1

7. 1. What is operating system?
• Exploits the hardware resources of one
or more processors
• Provides a set of services to system users
• Manages secondary memory and I/O
devices

8. 2. Computer hardware overview
•
•
Processor
Main Memory
– referred to as real memory or
– volatile
I/O modules
primary memory
•
–
–
–
secondary memory devices
communications equipment
terminals
• System bus
– communication among processors, memory, and
I/O modules

9. Computer System

10. Computer Components

11. Computer Components

12. Registers
The component that performs computation is CPU, or
more concretely it is the ALU (arithmetic logical unit)
in CPU that do the computation.
•
• To compute, we need first prepare input; however ALU
cannot access memory directly, Instead, a set of
registersare provided as a cache that is
smaller than main memory.
faster but
• (They are smaller between they are much more
expensive than regular memory.)

13. Processor Registers
The textbook reference categorizes registers
two types:
User-visible registers
– Enable programmer to minimize main-memory
references by optimizing register use
Control and status registers
– Used by processor to control operating of the
processor
– Used by operating-system routines to control the
execution of programs
• into
•
•

14. User-Visible Registers
May be referenced by machine language
Available to all programs - application
programs and system programs
Types of registers
– Data
– Address
•
•
•
•
•
•
Index
Stack Segment
Stack pointer
SS
SP

15. • Address Registers
– Index
• involves adding an index to a base value to
an address
Segment pointer
• when memory is divided into segments,
memory is referenced by a segment and an
offset
Stack pointer
• points to top of stack
get
–
–

16. Control and Status Registers
Program Counter (PC)
– Contains the address of an instruction to be fetched
Instruction Register (IR)
– Contains the instruction most recently fetched
Program Status Word (PSW)
•
•
•
–
–
–
condition codes
Interrupt enable/disable
Supervisor/user mode

17. Instruction Register
Fetched instruction is placed in the instruction• register.
Types of instructions:
– Processor-memory
• transfer data between processor and memory
Processor-I/O
• data transferred to or from a peripheral device
Data processing
• arithmetic or logic operation on data
Control
• alter sequence of execution
–
–
–

18. • Condition Codes or Flags
– Bits set by the processor hardware as a
result of operations
– Can be accessed
altered
Examples
by a program but not
–
•
•
•
•
positive result
negative
result
zero
Overflow

19. 2.3 Instruction execution

20. Instruction Fetch and Execute
• The processor fetches the instruction from
memory
• Program counter (PC) holds address of the
instruction to be fetched next
• Program counter is incremented after each fetch

21. Example of Program Execution
How a partial program is
two numbers.
executed step by step to add
Instruction
operand).
consists of from two parts (opcode,
Opcode: 1 Load, 2 Store, 5 Add
Operand: Data, Address,

22. Example of Program Execution

23. Example of Program Execution

24. Example of Program Execution

25. Example of Program Execution

26. Example of Program Execution

27. Example of Program Execution

28. Interrupts
• An interruption of the normal sequence of
execution
Improves processing efficiency•
• Allows the processorto
I/O
execute
operation
other
instructions
progress
while an is in
• A suspension of a process caused by an event
external to that process and performed in such
a way that the process can be resumed

29. Classes of Interrupts
Program•
–
–
–
–
arithmetic overflow
division by zero
execute illegal instruction
reference outside user’s memory space
•
•
•
Timer
I/O
Hardware failure

30. I/O processing with interrupts
(Interrupt Handler)
A program that determines nature of the interrupt
and performs whatever actions are needed.
•
• Control is transferred to this program
• Generally part of the operating system

31. Interrupt Cycle

32. Interrupt Cycle
Processor checks for interrupts•
• If no interrupts fetch the next instruction for
the current program
• If an interrupt is pending, suspend execution
of the current program, and execute the
interrupt handler