Computer System and its organization with different generations

about computers

1. 2 - Computer System
A computer system is made up of both
–Hardware
–Software
Software is another term for computer program.
Software controls the computer and makes it do useful
work.
Without software a computer is useless, just as a car
without someone to drive it.
To get a computer to perform a specific task it must be
given a sequence of unambiguous instructions called a
program written in some programming language.
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2. Hardware components of a computer system are the
electronic and mechanical parts.
It is the physical medium.
The major hardware components are:
–Processor
–Main memory & Secondary memory
–Input devices (keyboard)
–Output devices (printer)
The processor, main memory, and secondary memory
devices are inside the system unit seen as metal box.
The keyboard and monitor (the TV-like screen) are
input/output devices.
Hardware components also include
–mouse, disk drive, soundcard and speakers
–CD ROM drive (Read Only Memory), network card
–floppy disc drive (for backing up data) 2

3. Types of Computers
By 1980, computers were classified into three main types.
Main Frame:
–Traditionally large computers, often containing thousands of IC’s
and costing millions of dollars
–High speed, large storage & highly accurate
–can be shared by group of users
Mini Computers:
–Smaller in size, slow in speed, low cost and can be shared by
group of users
Micro Computers (Personal computer - PC):
–New class of general purpose machines intended for single user.
–Small in size and inexpensive
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4. Fig: Schematic diagram gives the layout of a
Digital Computer.
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5. CPU (Central Processor Unit) does the `work‘ of
fetching, storing and manipulating data that are
stored in the computers memory.
Main memory is used to store program and data
during execution of a program.
Disc drive (hard or floppy) used to store files
(program + data) `permanently‘.
Keyboard allows user to input information.
VDU (Visual Display Unit) visually outputs the
data.
Printer allows a hard copy to be made.
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6. The current architecture of PC (personal Computer) is as
follows (major hardware components ).
The arrows show the direction of data flow. 6

7. The bus is a group of wires on the main circuit board of
the computer through which electrical signal passes.
It is a pathway for data flowing between components.
Buses are of three types:
–Address bus:
•used to transmit address of memory location
–Data bus:
•Used to transmit data from/to memory
–Control bus:
•Supervises reading/writing of data
Most devices are connected to the bus through a
controller.
Controller coordinates the activities of the device and the
bus.
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8. Central Processing Unit (CPU)
The processor as its name suggests is the unit that does the
work of the computer system i.e. it executes computer programs.
Instructions in the program tell the processor
–when and what to read from a keyboard;
–what to display on a screen;
–what to store and retrieve from a disk drive and so on.
It can do arithmetic, compare numbers and perform
input/output. (read information and display or store it).
It has no magical powers. It is instructive to bear in mind that
all computer programs are constructed from sequences of
instructions based on such primitive operations.
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9. The processor itself is made up of a number of
components such as the
–Arithmetic logic unit (ALU) and
–Control unit (CU).
The ALU carries out arithmetic operations (e.g. addition
and subtraction) and logical operations (e.g. and, or, not)
The CU controls the execution of instructions.
Traditionally, the processor is referred to as the central
processing unit or CPU.
With the advent of microprocessors, the term MPU or
microprocessor unit is also used.
A microprocessor is simply a processor contained on a
single silicon chip.
Processors come in all different `shapes and sizes'
–There are many different types of architectures which are suited
to a variety of different tasks
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10. Main Memory
Main memory is where programs and data are kept
during execution that the processor is actively working
with.
when the processor is actively using them.
Main memory is also called Random Access Memory
(RAM) or primary memory.
"Random" means that the memory cells can be accessed
in any order randomly.
Main memory is:
–very closely connected to the processor.
–the contents are quickly and easily changed.
–interacts with the processor millions of times per second.
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11. Micro Computer Memory
It has two types of memory.
Random Access Memory (RAM)
–Volatile
–Random access to any memory location
–Read & write access
–Program + data reside in this memory
Read only Memory (ROM)
–Non volatile
–Only read access
–Permanent programs reside 11

12. Cache Memory
A special and very high speed memory used to
increase the speed of processing.
It lies between CPU and main memory.
It is expensive and usually small in size.
Stores only segments of programs currently being
executed by CPU.
It is also sometimes called buffer.
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13. Secondary memory
Connected to main memory through the bus and a
controller.
The contents are easily changed, but this is very slow
compared to main memory.
It is used for long-term storage of programs and data.
Common secondary storage devices are the hard disk
and floppy disks and CDs.
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14. •The hard disk
Has enormous storage capacity compared to main
memory (300 times the amount of storage in main
memory).
Storage capacity of 40/80 Gigabytes and Terabytes.
Usually contained in the systems unit of a computer.
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15. Quick comparison of two types of storages:
Primary memory
1.Fast
2.Expensive
3.Low capacity
4.Connects directly to
the processor
Secondary memory
1.Slow
2.Cheap
3.Large capacity
4.Not connected
directly to the
processor
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16. Some Basic Terminology
•Bit is short for Binary Digit.
–Bit has only two values represented as: 1 or 0, (on or
off ; true or false),
•Byte consists of 8 Bits.
•1 KB (1 KiloByte) contains 1024 Bytes.
•1 MB (1 MagaByte) consists of 1024 KB.
•1 GB (1 GigaByte) has 1024 MB.
•1 Terabyte consists of 1024 GB.
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17. Table of units of measurement
Name EquivalentNumber of Bytes power of 2
Byte 8 bits 1 2
0

Kilobyte (KB)1024 bytes1024 2
10
Megabyte (MB)1024 KB 1,048,576 2
20
Gigabyte (GB)1024 MB 1,073,741,824 2
30
Terabyte 1024 GB 1,099,511,627,776 2
40
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18. Organization of Main Memory
Main memory consists of a very long list of bytes.
In most modern computers, each byte has an address.
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19. Each row is called memory location (single byte and has
an address).
The addresses are the integers to the left of the boxes: 0,
1, 2, 3, 4, ... and so on.
The addresses for most computer memory start at 0 and
go up in sequence until each byte has an address.
The address of a byte is not part of its contents.
The bits at a memory location are called the contents of
that location.
Each location contains a pattern of eight bits, each bit is
either 0 or 1.
By the term that a computer has "128 MB of RAM" they
are talking about the size of memory.
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20. Groups of memory locations can be treated as a
whole to allow more information to be stored.
All machines have a wordsize: a fundamental unit
of storage,
Ex: 8-bits, 16-bits, etc.
The size of a word (in Bytes) differs between
machines.
A Pentium based machine generally has word size
of 32-bits. 20

21. The CPU can read to and write from a specified
memory location.
Most processors can write (and read) more than a
single byte at a time.
While writing a byte into a given location, the
previous bit pattern is destroyed and the new
contents (bit pattern) are saved for future use.
While reading a byte from a given location
–The processor gets the bit pattern stored at that
location.
–The contents of that location are NOT changed.
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22. CPU also has a small number (usually less than 100) of
storage locations to store information that are currently
being processed.
These locations are called registers and depending on the
processor, a register may typically store 8, 16, 32 or 64
bits.
Processors with a register size of
–n-bits are called n-bit processors,
–processors with 8-bit registers are called 8-bit processors,
–similarly there are 16-bit, 32-bit and 64-bit processors.
CPU has several important registers
–Memory address register (MAR)
–Memory data register (MDR)
–Program counter (PC)
–Current instruction register (CIR)
–Accumulator
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23. The greater the number of bits the more powerful the
processor is, since it will be able to process a larger unit
of information in a single operation.
Ex: a 32-bit processor will be able to add two 32-bit
numbers in a single operation whereas an 8-bit processor
will only be able to add two 8-bit numbers in a single
operation.
An n-bit processor will usually be capable of transferring
n-bits to or from memory in a single operation.
This number of bits is also referred to as the memory
word size. So, while a byte refers to an 8-bit quantity, a
word can mean 8, 16, 32, 64 or some other number of
bits.
On some machines a word is taken to mean a 16-bit
quantity and the term long word is used to refer to a 32-
bit quantity.
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24. Software
Software is a program and data that a computer uses.
Software is kept on some hardware device such as a hard disk
or floppy disk for further use.
Programs are lists of instructions for the processor.
Data can be any information that a program needs. It could be:
Character data, numerical data, image data, audio data, and
countless other types.
The distinction between programs and data within the
computer memory is not as clear-cut as you might think,
however.
However both programs and data are saved in computer
memory in the same way.
The electronics of computer memory (both main memory and
secondary memory) make no distinction between programs
and data.
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25. The programs and data can be saved using the same
electronic methods.
This is one of the most important ideas in computer science.
Computer systems can use their memory for whatever needs
arise.
A computer that is dedicated to running a program that
controls another device is an embedded system.
An embedded system is usually embedded inside the device
it controls.
Usually they run just one program that is permanently kept
in a special kind of main memory called ROM (for Read
Only Memory).
More processor chips are sold per year for embedded
systems than for all other purposes
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26. Types of Programs
There are two categories of programs.
–Application programs (usually called just
"applications") are programs that people use to get
their work done.
–Systems programs keep all the hardware and software
running together smoothly. It helps in developing
application programs.
The difference between "application program"
and "system program" is fuzzy.
Often it is more a matter of marketing than of
logic. 26

27. Application Programs
•Word processors
•Game programs
•Spreadsheets
•Data base packages
•Graphics programs
•Web browsers
Systems Programs
•Operating system.
•Networking system.
•Database system.
•Compilers
•Web site server.
•Data backup.
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28. Operating Systems (OS)
The operating system is a complex collection of many
programs that governs the control of various resources
such as:
–Processor
–Main Memory
–Secondary storage
–I/O devices
–Files
The operating system is software; the same hardware can
be used with many different operating systems (although
only one at a time.)
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29. Modules of OS
The operating system is always present when the
computer is running.
It coordinates the operation of all the hardware and
software components of the computer system.
The operating system is responsible for starting
application programs running and finding the resources
that they need.
The operating system manages the details of the
resources an application requires while it is running.
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30. There are various modules of OS
–Processor management
–Memory management
–Device management
–Information management
These modules resolve conflicts, optimize
performance and acts as an interface between the
user’s program and computer hardware.
Modern operating systems usually come with a
user interface that enables users to easily interact
with application programs by using windows,
buttons, menus, icons, the mouse, and the
keyboard.
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31. Ex: Operating systems are DOS, Unix, Linux,
Windows 98, Windows NT, Solaris, etc.
There are different OS for different kinds of
machines.
–Single user machine
–Batch processing
–Multiprogramming
–Time sharing
–Real time machines
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