Backing StorageDevices

Definition

• Backing storage devices are where you can store data permanently.

• This means that data is held when the computer is switched off and can be loaded onto a computer system when required.

Device MediaApprox

CapacityAccess

 

Floppy Disk Drive Floppy Disk 1.44Mb Random

 

CD-ROM drive CD-ROM

700Mb RandomCD Rewriter

CD-R

CD-RW

 

USB Flash Drive Flash ROM 1 - 8Gb Random

 

DVD-ROM Drive DVD-ROM

4.7Gb - 16Gb RandomDVD Rewriter

DVD-R

DVD-RW

 

Hard Disk Drive Hard Disk up to 5Tb Random

Computer memory

• Computers have two types of memory.

• These are:– Internal memory – Backing storage

Internal memory

• Internal memory is used by the computer to store programs and data that are currently being used. e.g. RAM (Random Access Memory).

• Internal memory is volatile memory.• Also called emptied memory(i.e. its contents

are lost) when the computer is turned off.

Internal memory…

• Internal memory can not hold all the data and programs that a computer might need.

• It only holds the data and programs that are in use at a particular moment in time

• It empties and refills itself as different programs and files are used.

Internal memory…

• Internal memory can not hold all the data and programs that a computer might need.

• It only holds the data and programs that are in use at a particular moment in time

• It empties and refills itself as different programs and files are used.

Backing storage

• Backing storage is a memory that is used to store data and programs that are needed to be used again and again.

• It is a non-volatile memory • e.g. Computer discs (floppy, hard, or CDs)

are often used as backing storage.

Backing Storage device…• Hard Disks are the main internal backing store usually

found inside computers.

• The main benefit of hard drives is that they have a large storage capacity e.g.

• 500 gigabytes or more.

External Backing Store Flash

• Flash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed.

• Developed from EEPROM (electrically erasable programmable read-only memory)

External Backing Store Floppy disks

• Floppy disks are a common external backing store, however only store up to 1.44 Mb of data.

• Excellent for transferring small files of data from one machine to another and for backing up important small files stored on your hard disk.

3.5 inch Floppy Disk

Disk inside plastic case Write Protect

Notch

Head Contact Area

Metal Hub

Positioning & Drive Hole

Centre Hole

External Backing Store…

• CD-ROM (Compact Disk Read Only Memory) disks are optical disks that use the same technology as musical compact disks.

• They store up to 700 Mb of data and a laser beam is used to read the data off the disk.

• What can they be used for?

• As CD-ROMs are much bigger than floppy disks,

Read Only Memory

• Read Only Memory is memory that is not lost when the computer is switched off.

• All computers have a small amount of ROM.• This is so that essential instructions can be

stored.

Read Only Memory…

• Instructions stored in the ROM enable the computer to check the hardware and load the operating systems.

Measuring computer memory

• A common system of measurement is used to measure computer memory.

• These are:– Bits– Bytes

Bits

• Computers use electronic circuits to perform the tasks they are programmed to complete.

• These circuits can be in one of two states - ‘On’ or ‘Off’.

Bits

• In computer programming, when a circuit is ‘On’ it is given the numerical value 1 in the binary system.

• In computer programming, when a circuit is ‘Off’ it is given the numerical value 0 in the binary system.

• Transistors are silicon chips can store these values (Binary Digits).

Bytes• Bytes are units of computer memory.• A byte is made up from eight bits.• Each character (letter, number, or punctuation

mark) on a standard QWERTY keyboard is made up of eight bits.

• These codes are common to all computer systems and are known as the ASCII Code (American Standard Code for Information Interchange).

Bytes

• The code for the letter ‘a’ is 97.• This is 01100001 in binary.

Bytes

128 64 32 16 8 4 2 1

0 1 1 0 0 0 0 1

64 32 1

The binary number 97 is made as follows:

64 + 32 + 1

Bytes• 1 kilobyte = 1,024 bytes (210).

• 1 megabyte =1,024 kilobytes =1,048,576 bytes (220)

• 1 gigabyte = 1,024 megabytes = 1,073,741,824 bytes (230).

• 1 terabyte = 1,024 gigabytes = 1,099,511,627,776 bytes

(240).

Types of memory

• There are two main types of memory.

• These are:– RAM (Random Access Memory)– ROM (Read Only Memory)

The End