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Technology and Computer Evolution Introduction to Computer Systems Computer Hardware Computer Software
Computer System Users
Types of User: End-user Applications Programmer Low-level Programmer and Hardware Designer
The End User
The vast majority of computer users are end users
View computers as tools – black boxes Use a set of application programs to achieve
a specific goal or to solve a specific problem: Word processor Spreadsheet CAD (Computer Aided Design) DTP (Desktop Publishing)
The End User
Purchase is based upon complete set of hardware and software according to application environment,
No need to have knowledge of design, implementation and testing at hardware and software level.
Applications Programmers
People who provide what end users want Computer Scientists or Engineers. Little knowledge of hardware Appreciation for business logic Technically and generally mathematically
literate
Low-Level Programmers and Hardware Designers Electronic engineers Computer scientists Knowledge of machine architecture (Why?) Knowledge of electronics Real-time, bit manipulation and hardware
resources Program in assembler and C Hardware design in FPGA, VHDL and more
rarely ASIC
Low-Level Programmers and Hardware Designers Advantage of using Assembly Language:
Used in industrial time critical applications In-depth understanding;
Instructions (arithmetic, Logical and I/O) Instruction phases (fetch, decode and execute) Information representation (pointers, data)
understanding of processor architecture.
Difference between pointers and data?
Machine Code Very simple low level instructions. A single high level language instruction (e.g. VB)
may require many machine code instructions. An integral part of the processor. An instruction has an operation code (opcode),
followed by zero or more items of data (operands)
© De Montfort University, 2007 CSCI1412-HW-3 9
A Microcomputer System
Three components: Hardware Software Data
Hardware
The physical equipment: Base unit – printed circuit boards (processor,
memory and I/O), power supply and connections Interface – VDU/monitor, keyboard and mouse Peripherals – Disks, CD/DVD, printers and
scanners
Hardware CPU Components
CU: Control Unit interprets stored instructions in sequence issues commands to all elements of the computer system
ALU: Arithmetic & Logic Unit performs arithmetic and logic instructions
Traditionally the CPU also included RAM: Random Access Memory
holds data, instructions and results of processing temporary (volatile)
Hardware Often, CPU is used to mean just the CU and
ALU the ‘processor’ or ‘microprocessor’ other physical
equipment: Base unit – printed circuit boards (processor, memory
and I/O), power supply and connections Interface – VDU/monitor, keyboard and mouse Peripherals – Disks, CD/DVD, printers and scanners
Hardware
notice that all information enters and leaves the CPU via the RAM
CPU
InputDevices
CommunicationDevicesBacking Storage
OutputDevices
controlunit
arithmetic & logic unit
RAM
(micro-)processor
Why CU and ALU are two separate entities?
Software
A sequence of instructions that tell the computer what to do
Controls the hardware Processes inputs and gives outputs Examples: linux, windows, internet explorer,
gcc, etc
Data
Inputs files Settings – registry, .ini files, .conf files Some cross over - batch files and shell
scripts
Terminology Bit (binary digit, ‘0’ or ‘1’) easy to represent as magnetic fields, light/electrical
pulses, etc. Byte a group of 8 bits nibble = 4 bits (a small byte!) Word a group of bits that can be manipulated by the
processor as a single unit almost always it is a whole number of 8-bit bytes
Terminology memory capacities are currently in billions of bytes disk capacities are in billions or trillions of bytes
Representation?
Kb = Kilobyte = 1024 bytes = 1024 8 bits = 210
Mb = Megabyte = 1024 Kb = (1024)2 bytes = 220
Gb = Gigabyte = 1024 Mb = (1024)3 bytes = 230
Tb = Terabyte = 1024 Gb = (1024)4 bytes = 240
Pb = Petabyte = 1024 Tb =(1024)5 bytes = 250
Instruction and Data Storage
Number representation Fundamental to all computer system is the notion
of a binary digit - 0 or 1 – called a bit. Decimal System (base 10) Binary System (base 2) Hexadecimal System (base 16) Octal System (base 8)
Instruction and Data Storage
Integers (a number with no decimal points) An unsigned byte – range 0 to 255
bit 7 6 5 4 3 2 1 0
value 27 26 24 24 23 22 21 20
value 128 64 32 16 8 4 2 1
01001101 = 1 + 4 + 8 + 64 = 77 10111101 = 1 + 2 + 8 + 16 + 32 + 128 = 187
Instruction and Data Storage
Negative Integers An twos compliment signed byte – range -128 to +127 Most significant bit stores the sign (1 for -, 0 for +) When negative, result = -128 + result
bit 7 6 5 4 3 2 1 0
value -/+ 26 24 24 23 22 21 20
value -128/+ 64 32 16 8 4 2 1 01001101 = 1 + 4 + 8 + 64 = 77 11001101 = -128 + 1 + 4 + 8 + 64 = -51
Instruction and Data Storage Hexadecimal
uses powers of 16:160 = 1161 = 16162 = 256163 = 4,096164 = 65,536165 = 1,048,576
0 = 01 = 12 = 23 = 34 = 45 = 56 = 67 = 7
8 = 89 = 9A =10B =11C =12D =13E =14F =15
Instruction and Data Storage
Real numbers Floating point binary representations are used to
represent real numbers (a number that has a decimal point)
It is possible to use fixed point binary representation, generally not used because of inflexibility
Instruction and Data Storage
Real numbers
3.141592654, 2.9979 108, 6.626 10-34
A number is split into two parts one part describes the number itself (the mantissa) another describes where the decimal point appears (the exponent)
Characters (text)
Text is a collection (an array) of characters Generally characters are encoded in ASCII
(American Standard Code for Information Interchange)
Example: “Hi!”
Character H i !
ASCII value 72 105 33
Binary 01001000 01101001 00100001
Low Level Computer Languages Assembly language
Direct interaction with all parts of the hardware Specific to each microprocessor Great for real-time execution Nearly impossible to code large tasks
Low Level Computer Languages Assembly language
Example on MC680000 seriesCLR.W D3
Clear the lower 16 bit the data register D3
High Level Computer Languages Higher level of abstract from the hardware Less direct interaction with the hardware Example languages:
C (can be low level) C++ Java BASIC FORTRAN COBOL
High Level Computer Languages Example in Cint D0 = 7 + 2 * (267 – 23);
Equivalent in MC680000 assemblerMOVE.L #267,D0
SUB.W #23,D0
ADD.W D0,D0
ADD.W #7,D0
Technology and Computer Evolution
Computer Generations
Computer systems are large collections of electronic switches
The power of a computer depends on the number of these electronic ‘binary’ switches
Computer Generations
First Generation (1940’s) Switches were thermionic valves Heated cathode produces negatively charged
electrons Flow of electrons to positive anode controlled by
charged grid Very large Prone to breakdowns
Computer Generations
Thermionic valve / vacuum tube
Computer Generations
Second Generation (1950’s) Switches were transistors The flow of electrons between an ‘emitter’ and a
‘collector’ is controlled by the current supplied to a ‘base’ semi conducting material
5mm in height Don’t breakdown
Computer Generations
The Transistor
Collector Emitter
Base
Computer Generations
Third Generation (1960’s) Switches were fabricated into small scale
integrated circuits (IC’s) Still use semiconductors Many transistors built onto a single chip Much smaller More processing power
Computer Generations
Forth Generation (1970’s to date) Miniaturization is the key Small scale integration 2 - 64 transistors Medium scale integration 64 - 2000 transistors Large scale integration 2000 - 64000 transistors Very large scale integration 64K – 200K
transistors Ultra large scale integration 200K – 100M +
transistors
Computer Generations
Moore’s Law Gordon Moore – co-founder of Intel Transistor density on IC’s will double every
eighteen months
Computer Generations
Computer Generations
Moore’s Law – the limit Research suggests that the smallest possible
transistor will be 16-nanometres Expected to be reached around 2020 Then what?
Quantum computing Bio computing Unknown alternative to the transistor
Computer Hardware
Computer Hardware
Computer Hardware
Components: CPU (Central Processing Unit) Co-Processor (floating-point math, graphics) Primary memory (RAM and ROM) Disk controller Input/Output devices and peripherals
Computer Hardware
Buses: Address bus – carries address of memory being
accessed Data bus – carries the data Control bus – carries control signals between
CPU and other components
Buses Computer memory is made up of a set of
locations. Each has a unique address. The address bus specifies the location. The
data bus transfers the data. The control bus determines e.g. read or write
45
The System Clock What controls the fetch / execute cycle?
the system clock this is a quartz chip that provides pulses at a
regular, rapid, rate, like a metronome n.b. not the same as the real date / time clock
The first microprocessor originally ran at 100 KHz, the Pentium IV is now at 1.2 – 4.0 GHz
A clock tick starts the fetch / execute cycle it may take several (perhaps tens of) clock ticks to
complete one complex instruction
© De Montfort University, 2007 CSCI1412-HW-3 46
GigahertzThe ‘simplest’ measure of speed is just the rate
at which the system clock ticks usually quoted in Gigahertz (GHz)
1 Hertz = 1 cycle per second 1 Megahertz = 1 million cycles per second 1 Gigahertz = 1 billion cycles per second
This is meaningful in one type of processor e.g. 2.4 GHz Pentium is twice as quick as 1.2 GHz
But is not for comparing different processor types different processors may take different numbers of
cycles to fetch / execute the ‘same’ instruction e.g. a Pentium takes X cycles to load a number into the
accumulator, whereas a 68040 takes Y cycles
© De Montfort University, 2007 CSCI1412-HW-3 47
Computer Hardware
Memory: Registers – store temporary data within the
processor Cache – stores temporary data that is likely to be
used with the processor Primary memory – RAM, stores programs being
executed Secondary memory – Disks, persistent storage
Computer Hardware
Memory: Organised as a table: 0
1
2
3
4
5
6
7
8
9
Computer Hardware
Inside the CPU
Clock
RAMExternal cache memory
ALU
Data Instruction
Internal cache memory
Control unit
Pipeline
DataAddress
Control
Computer Hardware
Inside the CPU – The Control Unit In overall control of the computer system Controls the fetch/execute cycle Registers:
Program counter – hold the memory address of the next word in the current instruction
Instruction register – holds the next instruction to be executed
Computer Hardware
Inside the CPU – Fetch/Excute Fetch
Fetch the instruction from memory. Decode it and it the instruction has a indirect memory address find out the effective address in memory.
Execute Execute the instruction by send the series of signals
from the control unit to the ALU. Store the result or send it to an output device.
The Fetch / Execute Cycle
53
control unit
RAM
arithmetic / logic unit
decode execute
fetch (store)
Computer Hardware
Inside the CPU – the Arithmetic/Logic Unit Integer arithmetic – addition, subtraction,
multiplication and division Logical operations – not, and, or, exclusive or
and Bit shift operations Data, address and status registers
Computer Hardware
Co-Processors Mathematical – to perform high speed floating
point number calculations Graphical – to produce video output from
computer models. Modern graphics co-processors often implement an API (DirectX, OpenGL) in hardware
Computer Software
Computer Software
System start-up Uses firmware (software stored in ROM) generally
called the BIOS, Basic Input/Output System Initialises hardware Performs Power On Self Test Starts the operating system
Computer Software
Operating System – OS Controls hardware and software Windows, Linux, MAC OS X Provides the initial front end experience to the end
user Does all the backroom work to keep things
running smoothly
Computer Software
Assemblers, Compilers and Interpreters Assemblers convert assembly language into
machine code Compilers convert text written a programming
language into machine code. Cross assemblers/compilers convert code into
machine code for a different machine Interpreters execute programming code on line at
a time
Computer Software
Java – the Exception Originally called Oak, java was intended to be the
de facto language for embedded systems The Java compiler javac converts java text in
machine independent byte code Each machine or piece of hardware has a Java
Virtual Machine (JVM) which converts byte code into machine code and executes it
Write once, run anywhere (slowly!)
Recap
Three types of people in computing:
Recap
Three types of people in computing: End users – our customers Applications programmers – people who
understand a little about computers and write all the software the we use. Use C, C++, Java, VB
Hardware programmers/designers – people who know a lot about electronics, they built gadgets and the software the underpins the applications software. Use VHDL, assembler, C
Recap
What is a Computer?
Recap
What is a Computer? A big collection of electronic binary switches The switches are actually very small transistors
jammed onto silicon wafers - chips CPU (Central Processing Unit) Co-Processor (floating-point math, graphics) Primary memory (RAM and ROM) Disk controller Input/Output devices and peripherals
