Storage Devices

Introduction

• A storage device is a hardware device capable of storing information. There are two storage devices used in computers; a primary storage device such as computer RAM and a secondary storage device such as a computer hard disk drive.

Parts of a Computer

• Monitor• System Unit• Keyboard• Mouse

System Unit

• Central Processing Unit Holds the central processor It is the brain of the computer Processes data and instructions

• Consists of :- Hard Disk RAM ROM CD-ROM drive Floppy Disk drive

Storage Devices

• RAM• ROM• Thumb Drive• CD-ROM• DVD-ROM• Hard Disc• Floppy Disc

RAM

• Stand for Random Access Memory• Random access memory is volatile memory, meaning it loses its contents once power is cut. • When a computer shuts down properly, all data located in random access memory is committed

to permanent storage on the hard drive or flash drive. At the next boot-up, RAM begins to fill with programs automatically loaded at startup, and with files opened by the user.

USEAllows the computer to read data quickly to run applications.

TYPESTwo types:1. Static RAM2. Dynamic RAM

DEFINITIONA form of data storage that can be accessed randomly at any time, in order and from any physical location

ROM

• Stand for Read Only Memory• Read Only Memory is a non-volatile memory as it is not

erased when the system is switched off.

USEStores the program required to initially boot the computer

TYPES

Types of ROM:-1. PROM2. EPROM3. EEPROM

DEFINITIONA form of data storage that cannot be easily altered or reprogrammed.

RAM vs ROM

RAM ROMRandom Access Memory Read Only Memory

Stores information temporarily Stores information permanently

Data can be changed Information inside cannot be changed

Data is lost when PC is switched off

Data is safe when PC is switched off

CD-ROM

• Compact Disc Read Only Memory• It is a optical disk capable of storing

large amounts of data - up to 1 GB, most common size is 650MB

• Single CD-ROM has storage capacity of 700 floppy disks, enough memory to store about 300,000 text pages

• Information stored cannot be changed

Advantages and Disadvantages

Advantages Disadvantages

Small and portable Fairly fragile, easy to snap or scratch

Very cheap to produce Smaller storage capacity than a hard drive or DVD

Most computers can read CDs. Slower to access than the hard disk

Fairly fast to access the data

Hard Disk

• It is the main, usually largest, data storage device in a computer

• Contains a number of metal platters which have been coated with a special magnetic material

• Also known as Magnetic Storage Device• Measured in Gigabytes, now it’s available

in Terabyte• Possible to have external hard disk which

can be plugged into the computer and used to back up your data

Advantages and Disadvantages

Advantages Disadvantages

Large storage capacity Far slower to access data than ROM and RAM chips

Stores and retrieves data much faster than a floppy disk

Can crash which stop the computer from working

Stored items are not lost when you switch off the computer

Regular crashes can damage the surface of the disk, leading to loss

data in that sector

Cheap on a cost per megabyte compared to other storage devices

It is fixed inside the computer and cannot easily be transferred to

another computer

Floppy Disk

• Oldest type of portable storage device

• It becomes obsolete• Can store up to 1.44 Mb of data -

equivalent to around 300 pages of A4 text

• Ideal storage for transferring small files

Advantages and Disadvantages

Advantages Disadvantages

Portable - small and lightweight Not very strong - easy to damage

Inexpensive Data can be erased if the disk comes into contact with a magnetic field

Useful for transferring small files Quite slow to access and retrieve data

Security tab to stop data from being written over

Can transport viruses from one machine to another

Can be used many times Small Storage capacity

Many new computers don’t have floppy disk drives

Flash Memory

• Typically Small, lightweight, removable and rewritable

• Consist of a small printed circuit board which is encased in plastic or metal casing

• Available from 1 Gb up to 16 Gb

Advantages and Disadvantages

Advantages Disadvantages

More compact, portable and cheap Can be easily be lost

Hold more data than floppy disk or even a CD

If handled roughly, it can be damaged

More reliable than floppy disk

Being developed with fashionable looking casing

BINARY CODE

Binary Codes

• A bit is a binary digit. It can only hold one of two values: 0 and 1

• Bits are usually assembled into group of eight to form a byte

• A byte contains enough information to store a single ASCII character

Units Used

Unit Equivalent1 bit A 1 or 0 (b)

4 bits 1 nybble (?)

8 bits 1 byte (B)

1 kilobyte (KB) 1,024 bytes

1 megabyte (MB) 1,048,576 bytes

1 gigabyte (GB) 1,073,741,824 bytes

1 terabyte (TB) 1,099,511,627,776 bytes

1 petabyte (PB) 1,125,899,906,842,624 bytes

Bit and byte

• 1 byte = 8 bits • Example:

Sekolah Menengah Rimba How many bytes are there: 22 bytes So, how many bits are there?

Answer: 176 bits To find the total bits, you need to multiply

the bytes with 8. Because 1 byte is equal to 8 bits.

ASCII

• Stand for American Standard Code for Information Interchange.

• It’s a 7 bit character code where every single bit represents a unique character.

• Why 7 bit? Because the minimum workable size is 1 byte, those 7 bits are

the low 7 bits of any byte. The most significant bit is 0. That means, in any ASCII file, you're wasting 1/8 of the bits. In

particular, the most significant bit of each byte is not being used.

• In the computer program, information is not being stored as characters. It is stored as ASCII codes. ASCII codes are stored as 1’s and 0’s.

• In fact, ASCII codes are basically binary codes.

ASCII to binary

ASCII ‘A’ ‘a’ ‘R’ ‘r’

Binary 0100 0001 0110 0001 0101 0010 0111 0010

Spare the jokes, when we enter a word example, “Computer”,it will program as:

0100001101101111011011010111000001110101011101000110010101110010

Now you try!!

• Find out how many bits and bytes in these sentence:-

Respectful, Responsible, Caring, Positive, Collaborative and Integrity is Sekolah Menengah Rimba’s School Values.

Answer: Bytes - 113 bytes, Bits - 113 * 8 = 904 bits