This document provides an introduction to computer systems and concepts related to program execution, interrupts, traps, instruction sets, I/O functions, compilers, interpreters, linkers, data representations, and bits and bytes. It discusses how programs are executed by loading code into memory and interacting with users or devices. Interrupts and traps are defined as mechanisms for notifying the operating system of external or internal events. The different types of instructions, interrupts, and compiler functions are also outlined.

1. INTRODUCTION TOCOMPUTER SYSTEM
CSC 2313
LECTURE 2B
Department of Maths and Computer-
Science
Faculty of Natural and Applied Science
BY
UMAR DANJUMA MAIWADA

2. PROGRAM EXECUTION
 Executing a program involves the creation of a process
by the operating system.
 The kernel creates a process by assigning memory and
other resources, establishing a priority for the process
(in multi-tasking systems), loading program code into
memory, and executing the program.
 The program then interacts with the user and/or other
devices and performs its intended function.
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3. INTERRUPTS
 An interrupt is the mechanism by which
notification of an external event that occurs
is communicated to the operating system.
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4. FUNCTIONS OF INTERRUPT
 An interruption of the normal sequence of execution
 Improves processing efficiency
 Allows the processor to execute other instructions
while an I/O operation is in progress
 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
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5. CLASSES OF INTERRUPTS
 Program interrupt: Generated by some condition that
occurs as a result of an instruction execution, such as
arithmetic overflow, division by zero, attempt to
execute an illegal machine instruction, and reference
outside a user's allowed memory space.
 Timer interrupts: Generated by a timer within the
processor. This allows the operating system to perform
certain functions on a regular basis.
 I/O interrupts: Generated by an I/O controller, to
assign normal completion of an operation or to signal a
variety of error conditions.
 Hardware failure interrupts: Generated by a failure,
such as power failure or memory parity error.
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6. TRAP
 A Trap is the notification of an internal event that
occurs while a program is executing, therefore it is
synchronous with the current activity of the
processor.
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7. INTERRUPT VS. TRAP
 An interrupt is a CPU event that is triggered by some external
device. A trap is a CPU event that is triggered by a
program. Traps are sometimes called software
interrupts. They can be deliberately triggered by a special
instruction, or they may be triggered by an illegal instruction or
an attempt to access a restricted resource.
 The operating system gets the control of the CPU when
either an external event (an interrupt) or an internal event (a
trap or exception) occurs.
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8. INSTRUCTION SETS
Instruction set architecture is the
structure of a computer that a machine
language programmer (or a compiler)
must understand to write a correct
(timing independent) program for that
machine
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9. COMPUTER-SYSTEM OPERATION
 Instruction Execution
A program to be executed by a processor consists of
a set of instructions stored in memory. In its simplest
form, instruction processing consists of two steps:
The processor fetches the instruction from
memory
 Program counter (PC) holds the address of the
instruction to be fetched next
 Program counter is incremented after each fetch
Instruction Register: Fetched instruction is placed in the
instruction register 9

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11. TYPES OF INSTRUCTIONS
 Processor-memory: transfers 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
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12. I/O FUNCTIONS
 An I/O module transfers data from external devices
to processor and memory, and vice versa. It
contains internal buffers for temporarily holding
data until they can be sent on.
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13. LANGUAGE COMPILERS AND
INTERPRETERS
 Compiler
 A compiler is a program that translates source code or
language e.g. C, COBOL, FORTRAN, C# into target
language (machine, assembly) which will be executed
directly on the machine.
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15. PUNCTUATION, CONSTANT ETC).
SYNTAX ANALYSIS: CHANGES THE LEXICAL UNIT INTO
HIERARCHICAL TREE LIKE STRUCTURE KNOWN AS
PARSE TREE IN WHICH EACH CHILD NODE
REPRESENTS THE ARGUMENT OF THE OPERATION
AND THE NODE REPRESENT THE OPERATION.
SEMANTIC ANALYSIS: THE SEMANTIC CHECKS
PROGRAMS GENERATED DURING THE SYNTAX PHASE
FOR ERRORS. AN IMPORTANT COMPONENT HERE IS
THE ERROR OF TYPE. FOR EXAMPLE, THE ABOVE
SHOWS HOW CONVERSION IS DONE FROM INTEGER
TO REAL TO AVOID TYPE ERROR.
SYMBOLIC TABLE: A DATA STRUCTURE WHICH
STORES INFORMATION ABOUT IDENTIFIERS AND
OTHER ATTRIBUTES. IT SPEEDS UP INFORMATION
RETRIEVAL ON AN IDENTIFIER.

16. INTERPRETER
 This is a simulated virtual machine which interprets
a program without necessarily interpreting it. It
allows easy implementation of source code. For
example, if an index of array is wrong, it can easily
show the line and index of error.
 An interpreter is slow because of complexity in
decoding from high level language instead of
machine language.
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17. LINKERS
 Is a computing program that takes one or more
objects generated by a compiler and combines
them into a single executable program.

18. DATA AND INFORMATION
REPRESENTATIONS
 What is data?
 Data can be defined as a representation of facts,
concepts or instructions in a formalized manner which
should be suitable for communication, interpretation, or
processing by human or electronic machine.
 Data is represented with the help of characters like
alphabets (A-Z,a-z), digits (0-9) or special characters(+,-
,/,*,<,>,= etc.).
 What is Information?
Information is organized or classified data
which has some meaningful values for the
receiver.
Information is the processed data on which
decisions and actions are based.
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19. BITS AND BYTES
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 The fundamental building block of computer storage is
the BIT. A bit may be OFF, so that its value is 0, or it
may be ON, so that its value is 1. A single bit does not
provide much information but it’s surprising what a
bunch of them could do.
 BYTES
 A group of nine related bits is called a byte, which represent
storage location both internally in memory and externally on
disk. Each byte consists of EIGHT BITS for data and ONE
bit for parity.

20. REFERENCES
1. Operating system by william stallings
2. OPERATING SYSTEM CONCEPTS by ABRAHAM
SILBERSCHATZ, Yale University, PETER BAER
GALVIN, Corporate Technologies, GREG GAGNE,
Westminster College
3. Operating system concepts by Silberschatz Galvin
Gagne.
4. Wikipedia.com
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21. QUESTIONS???
THANK YOU FOR YOUR ATTENTION
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