What is a Computer?
Device capable of performing computations and making
Computers process data under the control of sets of
instructions called computer programs
Personal computers: economical enough for individual
Distributed computing: computing distributed over
Client/server computing: sharing of information across
computer networks between file servers and clients
First generation computers
The first computers used vacuum tubes for circuitry
and magnetic drums for memory.
They were often enormous and taking up entire room.
First generation computers relied on machine
. They were very expensive to operate and in addition
to using a great deal of electricity, generated a lot of
heat, which was often the cause of malfunctions.
The UNIVAC and ENIAC computers are examples of
first-generation computing devices.
Second generation computers
• Transistors replaced vacuum tubes and ushered in the
second generation of computers.
• Second-generation computers moved from
cryptic binary machine language to symbolic.
• High-level programming languages were also being
developed at this time, such as early versions
of COBOL and FORTRAN.
• These were also the first computers that stored their
instructions in their memory.
Third generation computers
The development of the integrated circuit was the
hallmark of the third generation of computers.
Transistors were miniaturized and placed
on siliconchips, called semiconductors.
Instead of punched cards and printouts, users
interacted with third generation computers
through keyboards and monitors and interfaced with
an operating system.
Allowed the device to run many
different applications at one time.
Fourth generation computers
The microprocessor brought the fourth generation of
computers, as thousands of integrated circuits were
built onto a single silicon chip.
The Intel 4004 chip, developed in 1971, located all the
components of the computer.
From the central processing unit and memory to
input/output controls—on a single chip.
. Fourth generation computers also saw the
development of GUIs, the mouse and
Fifth generation computers
(present and beyond)
Fifth generation computing devices, based on artificial
Are still in development, though there are some
applications, such as voice recognition.
The use of parallel processing and superconductors is
helping to make artificial intelligence a reality.
The goal of fifth-generation computing is to develop
devices that respond to natural language input and are
capable of learning and self-organization.
Central Processing Unit
CPU (Central Processing Unit) also called the
Microprocessor or “The Brain” of the Computer.
Processor speed: The speed at which a
microprocessor executes instructions. This is usually
measured in megahertz (MHz).
Brands of Processors include:
Central Processing Unit
Computer chip: also called the
microprocessor may contain an
entire processing unit.
Computer chips contain millions
of transistors. They are small
pieces of semi-conducting
An integrated circuit is embedded
in the silicon. Computers are made
of many chips on a circuit board.
Data Storage Devices
The hard-drive is a mechanical
storage device typically located
Fast recording and recovery of
Large storage capacity
Primary storage device for data
Speed is measured in R.P.M.’s
Data Storage Devices (cont’d)
CD-ROM (compact disk read
Approximately 600 to 700
megabyte of storage
An optical device read by
a diode laser
Data Storage Devices (cont’d)
Floppy diskette is magnetic
storage device for small
amounts of data (1.44MB).
FLASH drive is a compact
and portable electronic
USB (plug and play)
Computer memory is binary (0 or 1) (on or off).
The byte is the standard unit of measurement.
A byte is composed of 8 bits (binary digits).
Typical units of measurement:
1 KB (kilobyte) = 1000 bytes
1 MB (megabyte) =1000 kilobytes or 1 million bytes
1 GB (gigabyte) =1000 megabytes or 1 billion bytes
RAM (random access memory)
stores data that is processing.
This type of memory is erased
when the computer is turned
ROM (read only memory)
contains special instructions for
the computer to operate.
Cache memory increases the
speed of the processor by
recording and anticipating
Screen resolution is measured in pixel per
inch (ppi), and printer resolution is
measured in dots per inch (dpi).
Computer screen resolution is approximately
Width x Height (Pixels) Video Display
640 x 480 Low Resolution
800 x 600 Medium Resolution
1600 x 1200 High Resolution
a sequence of instructions to accomplish a result
a computer processes information under the direction of
information to be processed by a program
Data: for each employee, the employee number, hours
worked & hourly pay rate
Program: instructions on how to process the data to
produce pay cheques, payroll register, etc.
Processing Device (Arithmetic/logic/repetition)
Central Processing Unit (CPU)
286, 386, 486, Pentium, K5, K6
Has three basic parts
Arithmetic Logic Unit (ALU)
executes all the arithmetic and logic instructions
decodes instructions and determines which is next to be
Buses are paths for information entering/exiting the CPU
Registers are memory for processing information
The Central Processing Unit
The CPU continuously follows the fetch-
Retrieve an instruction from main memory
Determine what the
Carry out the
Primary and secondary
Primary Storage (main memory)
On board memory (located on the motherboard)
Very fast, but expensive
RAM – Random Access Memory
ROM – Read Only Memory
RAM - Random Access Memory
Contents lost when computer is turned off (volatile)
A program must be in RAM for it to execute
128 to 256MB for a typical desktop computer
ROM - Read Only Memory
Read but not write capability
Permanent (non volatile)
Stores the preliminary instructions to be executed when
the computer is turned on, for example
To check RAM
To check communications with peripheral devices
Bootstrap loader program
Secondary Storage (secondary memory)
External devices (not on the motherboard); either
inside or outside the computer
Store programs and data permanently
Slower, but cheaper
RAM - nanoseconds, Drive - milliseconds
Floppy Disk - 1.4MB (portable)
Zip Drive - 100-750MB (portable)
CD - 650MB (portable)
Jaz Drive – 1-2GB (portable) discontinued
Hard Disk Drive >=20GB (not portable)
Tape - 50GB (portable, very slow)
Flash drives (portable)
For connecting peripheral devices
USB, Parallel and serial ports
Modem (internal or external)
For communicating over telephone lines
A computer program is a series of instructions
each instruction is expressed in a format consistent with
a predefined set of rules
a computer processes data under the direction of the
instructions in a program
there are instructions to input, process, store and output
the user of a program (as distinct from its creator) has
no need to be aware of the details of its construction
the user is only interested in the services that the
program is able to provide
instructions coded using combinations of 0’s & 1’s
assembly languages (low-level symbolic languages)
instructions coded using letters & numbers
one assembly language instruction is translated into one
machine language instruction
high-level symbolic languages
one instruction generates multiple machine language
4th generation programming languages
code “what” not “how”
HIGH LEVEL ASSEMBLY MACHINE
z = x + y MOV AL, X 0010 1001 0001
MOV AH, Y 0010 1100 0010
ADD AL, AH 0100 0001 0010
MOV Z, AL 0010 0010 1011
controls all machine activities
provides the user interface to the computer
manages resources such as the CPU and memory
Windows XP, Unix, Linux, Mac OS
generic term for any other kind of software
word processors, games, . . .
Most operating systems and application programs have a
graphical user interface (GUI)
The most important software on a computer
always running to perform the following tasks
create and manage files
control information going to/from the peripherals
create and manage files - several programs
run programs - COMMAND.COM
peripherals - IO.SYS, MSDOS.SYS
An electronic device, operating under the control of
instructions stored in its own memory unit, that can
accept data (input), manipulate the data according
to specified rules (process), produce information
(output) from the processing, and store the results
for future use.
What does a computer do?
Control Unit/Arithmetic Logic
Any hardware component that allows you
to enter data, programs, commands, and
user responses into a computer
Output devices make the information resulting from
processing available for use
Output Device Examples
Floppy disk, or diskette
Compact Disc CD-R, CD-RW, CD-
DVDs – DVD-ROM, DVD-R, DVD-
Flash disk/USB drive
The motherboard, or system board, is the main circuit
board of the system unit
The processor, also called the central processing unit
(CPU), interprets and carries out the basic instructions
that operate a computer
The control unit interprets the instructions
The arithmetic/logic unit (ALU) performs the logical and
Memory, also called random access memory, or RAM,
consists of electronic components that store data,
instructions, and information, as needed by the