CS101: Introduction to Computing

Instructors: Badre Munir, Usman Adeel, Zahid Irfan & Maria Riaz

Faculty of Computer Science and Engineering

GIK Institute of Engineering Sciences and Technology

Fall 2009

Data Representation

Data Representation

Modern computers are digital devices A digital device works with discrete data, such as the

digits 1 and 0 An analog device works with continuous data

Just as a standard light switch is a simpler technology than a dimmer, so is digital when compared to analog

digital analog

Number System We use decimal number system [base 10] when

representing numeric values in our daily life E.g., consider the number 123

123 = 100 + 20 + 3 = 1*102 + 2 * 101 + 3*100

Most modern computer systems do not use the decimal system to represent numeric values. Instead, they use a binary numbering system [base 2]

Consisting of only two digits: 1 and 0 Uses powers of 2 rather than 10

It is said that there are 10 types of people: those who understand binary, and those who don’t !

Conversions Conversion from binary to decimal:

(1011)2 = 1*23 + 0*22 + 1*21 + 1*20 = (11)10

Conversion from decimal to binary:1252

62 – 12

31 – 02

15 – 12

7 – 12

3 – 12

1 – 12

(125)10

= (1111101)2

162

8 – 02

4 – 02

2 – 02

1 – 02

(16)10

= (10000)2

Char Decimal Binary

A 65 100 0001

B 66 100 0010

0 48 011 0000

1 49 011 0001

$ 36 010 0100

Some decimal values & their binary equivalents

In addition to numeric data, computers also manipulate character data

numbers, symbols, numerals that are not used in arithmetic operations

To represent them, codes have been developed that specify binary equivalent for each character ASCII – 7 bits [Example table given ]

Unicode – 16 bits

Sounds and pictures must be transformedinto a format the computer can understand A computer must digitize colors, notes, and

instrument sounds into 1s and 0s

Representing Non-Numeric Data

Quantifying Bits and Bytes A bit is one binary digit (b):

can have value either 0 or 1

A byte is 8 bits (B) 0010 0100

Kilo- means a 1000; Mega- means million; Giga -means billion Kilobit (Kb) is 1,024 bits Kilobyte (KB) is 1,024 bytes Megabyte (MB) is 1,048,576 bytes Gigabyte (GB) is 1,073,741,824 bytes

Bits take the form of electrical pulses that can travel over circuits Almost the same way as electricity flows over a wire when you turn on a

light switch

Computer Hardware

Microprocessor

Memory

Storage Devices

I/O Devices

Computer Chips (-1-) Most electronic components inside a

computer are integrated circuits Thin slices of silicon crystal packed with

microscopic circuit elements Semiconducting materials are

used to fabricate a chip Types of chips:

DIPs; DIMMs; PGAs; SEC cartridge *The motherboard houses all essential chips and

provides connecting circuitry between them

Computer Chips (-2-)

Dual In-line Memory Module(DIMM)

Dual In-linePackage(DIP)

PinGridArray(PGA)

SingleEdgeContact(SEC)

Microprocessor

An integrated circuit designed to process instructions - CPU on a chip

The CPU has two parts ALU (arithmetic logic unit)

Performs arithmetic operations Performs logical operations Uses registers to hold data being

processed Control Unit

Directs and coordinates processing

Random Access Memory (RAM)

A temporary holding area for data, application program instructions, and the operating system As you type, characters are held in RAM

RAM is primary storage (main memory) Measured in megabytes (MB) or gigabytes (GB)

Today’s computers have between 256 MB and 2 GB of RAM depending on software you use You can purchase additional RAM A computer can use disk storage to simulate RAM. This is called

virtual memory Not as fast as RAM

Types of RAM RAM components vary in speed, technology,

and configuration SDRAM (Synchronous Dynamic RAM) RDRAM (Rambus Dynamic RAM) DDR DDR2 DDR3

Speed is measured in nanoseconds. 1 nanosecond (ns) is 1 billionth of a second It can also be expressed in MHz (millions of cycles per

second)

Other Types of Memory Read-Only Memory (ROM)

Type of memory circuitry that holds the computer’s startup routine

Permanent and non-volatile Only way to change the instructions on a ROM chip is to

replace the chip Additionally, a computer needs a semi-permanent

way of keeping boot data CMOS memory holds data but requires very little power

to retain its contents Retains important computer settings after you turn the power off Can be run by a battery on the motherboard

Storage Devices

A storage medium is the disk, tape, CD, DVD, paper or other substance that contains data

A storage device is the mechanical apparatus that records and retrieves data from a storage medium

Types of storage devices Magnetic Storage Optical Storage Solid State Storage

Magnetic Storage

Stores data by magnetizing microscopic particles on the disk or tape surface

Contains a read-write head mechanism in the disk drive that reads and writes

magnetized particles that represent data Example

Hard Disk Drive [HDD] Floppy Disk Magnetic Tape

Magnetic Storage : HDD Working of a hard disk

Hard disk platter - a flat, rigid disk made of aluminum or glass and coated with magnetic iron oxide particles

Hard disk - one or more platters and their associated read-write heads Capacity up to 250 GB; Preferred type of main storage

Limitations Head crash - when a read-write head runs

into a dust particle or other contaminant on the disk Head crash damages some data

on disk Triggered by jarring the hard disk

while in use Not limited to hard disks R/W

Head

Platter

Optical Storage Stores data as microscopic light spots (lands) and

dark spots (pits) on the disk surface Advantage

Less susceptible to environmentaldamage than data recorded on magnetic media

Example CD [Capacity: 700 MB]

DVD [Capacity: 4.7 GB; Double Layered can store up to 8.5 GB]

Blue-Ray [Capacity: up to 50 GB]

Optical Storage : CD / DVD

Working of CD / DVD Recordable technology uses a laser to change

the color in a dye layer sandwiched beneath the clear plastic disk surface

Rewritable technology uses “phase change” technology to alter a crystal structure on the disk surface

Slower than hard disk Not a suitable replacement for hard disk yet

Solid State Storage Stores data in a non-volatile, erasable, low-power chip Some solid state storage requires a device called a

card reader to transfer data to or from a computer Advantage

Provides faster access to data than magnetic or optical storage technology because it includes no moving parts

Portable Example

USB flash drive CompactFlash card

Moore’s Law:An Important Observation (-1-)

Moore's law describes a long-term trend in the history of computing hardware

Since the invention of the IC in 1958, the number of transistors that can be placed inexpensively on an IC has increased exponentially, doubling approximately every two years

Moore’s Law:An Important Observation (-2-)

References

Computer Concepts, by Parsons & Oja [Chapters 2]

http://en.wikipedia.org/wiki/ASCII http://en.wikipedia.org/wiki/Moore's_law