Computer System Architecture Lecture Note 1: introduction

Computer System Architecture
CSC 203 1.5
Budditha Hettige
Department of Statistics and Computer Science
University of Sri Jayewardenepura
1
Budditha Hettige
http://www.dscs.sjp.ac.lk/~budditha/index.php

IntroductionIntroduction
Budditha Hettige http://www.dscs.sjp.ac.lk/~budditha/index.php 2

What is Computer?What is Computer?
• Is a machine that can solve problems for
people by carrying out instructions given to it
• The sequence of instructions is call Program
• The language machine can understand is call
machine language
3Budditha Hettige http://www.dscs.sjp.ac.lk/~budditha/index.php

What is Machine Language?What is Machine Language?
• Machine language(ML) is a system of instructions and
data executed directly by a computer's Central Processing
Unit
• The codes are strings of 0s and 1s, or binary digits (“bits”)
• Instructions typically use some bits to represent
– Operations (addition )
– Operands or
– Location of the next instruction.

Machine Language contd..Machine Language contd..
• Advantages
– Machine can directly access (Electronic circuit)
– High Speed
• Disadvantages
– Human cannot identify
– Machine depended
(Hardware depended)

More on MachinesMore on Machines
• Machine defines a language
– Set of instructions carried out by the machine
• Language defines by the machine
– Machine executing all the program, writing in the
language
Machine LanguageLanguageLanguageLanguage

Two Layer (Level) MachineTwo Layer (Level) Machine
• This machine
contains only New
Language (L1) and
the Machine
language (LO)
Virtual Machine (L1)
Machine Language (L0)
Translate/
Interpreter
MachineMachine
Virtual
Machine
(L1)
Machine
Language
(L0)

Translation (LTranslation (L11 →→ LL00))
1. Replace each instruction written in L1 in to LO
2. Program now execute new Program
3. Program is called compiler/ translator

InterpretationInterpretation
• Each instruction in L1 can execute through the
relevant L0 instructions directly
• Program is call interpreter

Multi Level MachineMulti Level Machine
High-level Language Program (C, C++)
Assembly Language Program
Machine Language

Multilevel MachineMultilevel Machine
Virtual Machine Ln
Virtual Machine Ln-1
.
.
.
Machine Language L0

Six-Level MachineSix-Level Machine
• Computer that is designed up to the 6th level of computer
architecture

Digital Logic LevelDigital Logic Level
• The interesting objects at this level are gates;
• Each gate has one or more digital inputs (0 or 1)
• Each gate is built of at most a handful of
transistors
• A small number of gates can be combined to
form a 1-bit memory, which can store a 0 or 1;
• The 1-bit memories can be combined in groups
of, for example, 16, 32 or 64 to form registers
• Each register can hold a single binary number
up to some maximum;
• Gates can also be combined to form the main
computing engine itself.

Microarchitecture levelMicroarchitecture level
• A collection of 8-32 registers that form a local
memory and a circuit called an ALU
(Arithmetic Logic Unit) that is capable of
performing simple arithmetic operations;
• The registers are connected to the ALU to form
a data path over which the data flow;
• The basic operation of the data path consists of
selecting one or two registers having the ALU
operate on them;
• On some machines the operation of the data
path is controlled by a program called a
microprogram, on other machine it is
controlled by hardware.

Data PathData Path

Instruction Set Architecture LevelInstruction Set Architecture Level
• The ISA level is defined by the
machine’s instruction set
• This is a set of instructions carried
out interpretively by the
microprogram or
hardware execution sets

Operating System LevelOperating System Level
• Uses different memory organization, a new set of
instructions, the ability to run one or more
programs concurrently
• Those level 3 instructions identical to level 2’s
are carried out directly by the microprogram (or
hardwired control), not by the OS;
• In other words, some of the level 3 instructions
are interpreted by the OS and some of the level 3
instructions are interpreted directly by the
microprogram;
• This level is hybrid

Assembly Language LevelAssembly Language Level
• This level is really a symbolic form
for the one of the underlying
languages;
• This level provides a method for
people to write programs for levels 1,
2 and 3 in a form that is not as
unpleasant as the virtual machine
languages themselves;
• Programs in assembly language are
first translated to level 1, 2 or 3
language and then interpreted by the
appropriate virtual or actual machine;
• The program that performs the
translation is called an assembler.

Between Levels 3 and 4Between Levels 3 and 4
• The lower 3 levels are not for the
average programmer – Instead they
are primarily for running the
interpreters and translators needed
to support the higher levels;
• These are written by system
programmers who specialise in
developing new virtual machines;
• Levels 4 and above are intended for
the applications programmer
• Levels 2 and 3 are always
interpreted, Levels 4 and above are
usually, but not always, supported
by translation;

Problem-oriented Language LevelProblem-oriented Language Level
• This level usually consists of
languages designed to be used by
applications programmers;
• These languages are generally called
higher level languages
• Some examples: Java, C, BASIC,
LISP, Prolog;
• Programs written in these languages
are generally translated to Level 3 or
4 by translators known as compilers,
although occasionally they are
interpreted instead;

Multilevel Machines: HardwareMultilevel Machines: Hardware
• Programs written in a computer’s true machine language (level 1)
can be directly executed by the computer’s electronic circuits (level
0), without any intervening interpreters or translators.
• These electronic circuits, along with the memory and input/output
devices, form the computer’s hardware.
• Hardware consists of tangible objects:
– integrated circuits
– printed circuit boards
– Cables
– power supplies
– Memories
– Printers
• Hardware is not abstract ideas, algorithms, or instructions.

Multi level machine SoftwareMulti level machine Software
• Software consists of algorithms (detailed instructions
telling how to do something) and their computer
representations-namely, programs
• Programs can be stored on hard disk, floppy disk, CD-
ROM, or other media but the essence of software is the set
of instructions that makes up the programs, not the physical
media on which they are recorded.
• In the very first computers, the boundary between hardware
and software was crystal clear.
• Over time, however, it has blurred considerably, primarily
due to the addition, removal, and merging of levels as
computers have evolved.
• Hardware and software are logically equivalent

The Hardware/Software BoundaryThe Hardware/Software Boundary
• Any operation performed by software can also be
built directly into the hardware;
• Also, any instruction executed by the hardware
can also be simulated in software;
• The decision to put certain functions in hardware
and others in software is based on such factors as:
– Cost
– Speed
– Reliability and
– Frequency of expected changes

ExercisesExercises
1. Explain each of the following terms in your
own words
– Machine Language
– Instruction
1. What are the differences between
Interpretation and translation?
2. What are Multilevel Machines?
3. What are the differences between two-level
machine and the six-level machine

Computer System Architecture Lecture Note 1: introduction

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