basic machine architecture
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Basic Machine Architecture
Lecture Code: CIT 210
Bowen University, Iwo Nigeria
Learning Objectives: Students’ will learn the basic architecture of a simple
computer, and component of CPU in code execution
Targeted Students: 200 Level
Course Title: Foundation of Sequential Programming
A computer is an electronic device that manipulates information, or data. It has the ability to store, retrieve, and process data.
A computer is a programmable device that stores, retrieves, and processes data
In programming or to understand how to program a computer, it is necessary to
understand a bit about how computers are structured internally
While a program is a set of instruction given to the computer to
perform specific task, in computer, the CPU executes each instruction
provided to it, in a series of steps, this series of steps is called Machine
Cycle, and is repeated for each instruction.
Basic Computer System
Structure of a Computer System
1.Input Unit
2.Output Unit
3.Storage Unit
4.Arithmetic Logic Unit
5.Control Unit
Computer system has five basic units that help the computer to perform operations, which are given below:
The main components in a typical computer system are the processor, memory, input/output devices, and the
communication channels that connect them.
Everything that a computer does, from typing a word
document, to web browsing, printing, involves moving and
processing numbers. The electronics of a computer is
nothing more than a system designed to hold, move, and
change numbers.
The computer manipulates the data by performing operations on the numbers. No doubt, the CPU executes the programs the computer runs
As computer continues to process, store, and retrieve data. Data may be numbers in a spreadsheet, characters of
text in a document among others.
All data is stored in the computer as numbers.
Overview of a Processor
The processor is the most important part of a computer, the component around which everything else
is centered. In essence, the processor is the computing part of the computer.
The instructions are also known as opcodes or machine code
A sequence of instructions is what constitutes a program.
Instructions in a computer are numbers, just like data.
A processor is an electronic device capable of manipulating data (information)
in a way specified by a sequence of instructions.
• A machine-code program is a sequence of machine-code instructions.
• To be executed, a machine-code program must be stored in main memory.
• Code execution takes place within the CPU.
• The Code Execution Process follows ‘Fetch-Decode-Execute’ cycle
Program Execution Sequence
A sequence of instructions is a machine-code program. Each type of processor has a different instruction set,
meaning that the functionality of the instructions (and the bit patterns that activate them) varies
The instruction set provides commands to the processor, to tell it what it needs to do. The instruction set consists of
addressing modes, instructions, native data types, registers, memory architecture, interrupt, and exception
handling, and external I/O.
.
Central Processing Unit
The central processing unit (CPU) of a computer is a piece of
hardware that carries out the instructions of a computer
program. It performs the basic arithmetical, logical, and
input/output operations of a computer system.
The CPU is like the brains of the computer - every instruction,
no matter how simple, has to go through the CPU.
•CPU performs all types of data processing operations.
•It stores data, intermediate results, and instructions (program).
•It controls the operation of all parts of the computer.
CPU – Control Unit
The control unit Performs the following Operations :
1. Fetch from memory the next instruction to be executed
2. Decode it, that is, determine what should be done
3. Execute it by issuing the appropriate command to the ALU,
memory, and I/O Controllers
These steps are repeated over and over again until we reach the last instruction of a
program (usually HALT, STOP, or QUIT).
Arithmetic Logic Unit
ALU takes the data from Memory registers; ALU contains the
logical circuit to perform mathematical operations like
subtraction, addition, multiplication, division, logical operations
and logical shifts on the values held in the processors registers
or its accumulator
All information in a computer is stored and manipulated in the
form of binary numbers, i.e. 0 and 1. Transistor switches are
used to manipulate binary numbers since there are only two
possible states of a switch: open or closed. An open transistor,
through which there is no current, represents a 0. A closed
transistor, through which there is a current, represents a 1
Other logic gates are NOR, XOR , NOT
CPU- Main Memory
Main memory is where programs and data are kept when the
processor is actively using them. When programs and data
become active, they are copied from secondary memory into
main memory where the processor can interact with them
Computer memory is the storage space in the computer, where
data is to be processed and instructions required for processing
are stored.
Also, Cache memory is a very high speed semiconductor
memory which can speed up the CPU. It acts as a buffer
between the CPU and the main memory
System BUS
A bus is a common pathway through which information
flows from one computer component to another. This
pathway is used for communication purpose and it is
established between two or more computer components.
System bus:- This is the bus that connects the CPU to the
main memory on the motherboard. The system bus is also
called the front-side bus, memory bus, local bus, or host
bus.
Data sharing, Addressing, Timing, and Power are basic functional components of a computer Bus
Program Execution in the CPU
1. A sequence of instructions is stored in memory.
2. The memory address where the first instruction is located is copied to the program counter.
3. The CPU sends the address in the program counter to memory via the address bus.
4. Memory responds by sending a copy of the state of the bits at that memory location on the data bus, which the CPU then copies into its instruction register.
5. The instruction pointer is automatically incremented to contain the address of the next instruction in memory.
6. The CPU executes the instruction in the instruction register.
7. Go to step 3
Steps 3,4 & 5 are called an instruction fetch. Steps 3 -7 make up a cycle, the instruction execution cycle
A program counter (PC) is a CPU register in the
computer processor which has the address of the next
instruction to be executed from memory. A program
counter is also known as an instruction counter,
instruction pointer, instruction address register or
sequence control register.
An instruction register holds a machine instruction that is currently being executed. Generally, a
register sits at the top of the memory hierarchy. A variety of registers serve different functions
in a central processing unit (CPU) – the function of the instruction register is to hold that
currently queued instruction for use.
Program counter VS Instruction Register
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4. Computer Organization and Architecture: Designing for Performance, 8/e (Old Edition) by Stallings William
References
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