Storage Devices

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Hardware and Networks

Storage Devices

Teacher’s notes included in the Notes PageFlash activity. These activities are not editable.

Web addresses

Icons key: For more detailed instructions, see the Getting Started presentation


Learning objectives


Understand that computers store binary digits.

Know the difference between bits and bytes.

Know the difference between ROM and RAM.

Understand that there are different types of storage devices which hold varying amounts of data.


A computer only understands the numbers 0 or 1, or whether a switch is on or off.

We call those 1s and 0s ‘bits’ – binary digits.

A byte (made up of 8 bits) is enough computer memory to store a single character of data (e.g. the letter F).

The computer uses a code to understand what each bit pattern means.

Using the ASCII code, for instance, the letter F is 70 and has a bit pattern of 01000110.

Bits and bytes


ASCII for Capital Letters

65 A 78 N

66 B 79 O

67 C 80 P

68 D 81 Q

69 E 82 R

70 F 83 S

71 G 84 T

72 H 85 U

73 I 86 V

74 J 87 W

75 K 88 X

76 L 89 Y

77 M 90 Z

American Standard Code for Information Interchange (ask-ee) is a code which represents English characters as numbers. Each letter is assigned a number. For example, A = 65.

Most computers use ASCII codes. This makes it possible to transfer data from one computer to another by changing the ASCII code into a binary pattern.

ASCII


ASCII


When we write numbers in the decimal system, we write them in columns. Each column is ten times bigger than the one before (right to left).

Tens of millions

millions 100000s

10000s 1000s

100s 10s 1s

1 0 1 0

So 1010 is 1000 plus 10 = 1010.

Tens of millions

millions 100000s

10000s 1000s

100s 10s 1s

1 1 0 1 0

11010 would be 10000 plus 1000 plus 10 = 11010.

Decimal and binary


In the binary system, everything is based on 2s, not 10s, so each column is twice as big as the one before.

128s 64s 32s 16s 8s 4s 2s 1s

1 0 1 0

So 1010 in binary is 8 plus 2 = 10.

128s 64s 32s 16s 8s 4s 2s 1s

1 1 0 1 0

11010 would be 16 plus 8 plus 2 = 26.

Decimal and binary


Binary patterns


All computer data is stored in binary form.

This not only includes text, but images, sounds and movies as well.

The more complex the data, the more memory is used to store it.

Binary patterns

This does not take up asmuch memory… …as this.


The amount of data stored is measured in kilobytes (KB).

Confusingly, 1KB is actually 1,024 bytes (210), not 1,000 as you might expect, but most people think in multiples of 1,000.

1 megabyte (MB) is 1,000 KB (220)1 gigabyte (GB) is 1,000 MB (230)1 terabyte (TB) is 1,000 GB (240).

Data storage


Match the pairs


When a computer is first switched on, it needs to load up the BIOS (Basic Input/Output System) and basic instructions for the hardware.

These are stored in ROM (Read Only Memory).

This type of memory is called non-volatile because it retains the data.

Data stored in ROM remains there even when the computer is switched off.

ROM can be found on the motherboard.

Read Only Memory (ROM)


Computers store temporary data in the RAM (Random Access Memory). These could be operating instructions, loose bits of data or content from programs that are running.

The contents of RAM are constantly rewritten as the data is processed.

When the computer is switched off, all the data is cleared from the RAM.This type of memory is called volatile because it only stores the data whilst the computer is switched on.

RAM sticks are found on the motherboard.

Random Access Memory (RAM)


RAM and ROM


Computers need backing storage outside the CPU to store data and programs not currently in use.There are three main types of storage device:

Those that store data by magnetizing a special material that coats the surface of a disk.

Those that store data using optical technology to etch the data onto a plastic-coated metal disk. Laser beams are then passed over the surface to read the data.

Flash drives use solid state technology and store data in a similar way to the BIOS chip.

Types of backing storage


Types of backing storage

The medium is what the data is actually stored on. Examples of media include floppy disks, CD-ROMs and zip disks.

Floppy disks hold about1.44 MB of data.

Zip disks store up to750 MB of data.

CDs hold around 700 MB of data.


The hard disk of the computer stores the system information, programs and data that the computer uses every day.

Computer servers will use RAID systems with many hard drives to provide huge capacity and safer storage. The drives can be mirrored so that data written to one of them is also written to others, so if one drive fails, the others just take over.

Removable hard drives plug into the USB port and can be used for backup or transfer of data to another computer.

Backing storage – hard drives


Floppy disks used to be used a lot, but they are unreliable and don’t hold very much data, so they are rarely used now.They hold 1.44 MB of data, so are only really useful for backing up or moving small files that don’t contain graphics.They are easily damaged, which means that files stored on them won’t always load.As flash memory has become cheaper, many new computers don’t even have a floppy disk drive.

Backing storage – floppy disk drives


There are two main types of optical storage: CD and DVD. They look exactly the same, but DVDs hold much more data than CDs and need different drives to read them.

CD-ROMs are read only – you can read data from them but can’t write more data to them.CD-Rs allow you to write data once, but you can’t write over it. CD-RWs allow you to write data and then record new data over it.DVD-Rs and RWs follow the same pattern.You need special software to write to CDs and DVDs – you cannot simply copy files to them.

Backing storage – optical


In recent years, flash memory has become much more popular.

It holds a lot of data in a very small space. It doesn’t need special software to use it. Most computers will recognize the device as soon as you plug it in.Flash memory sticks connect through USB or FireWire ports.Many other devices, like digital cameras and MP3 players, also use flash memory.Flash memory cards can hold different types of data so your MP3 player could hold a data file with your homework on it, for example.

Backing storage – flash memory


Optical or magnetic


Storage capacity


Fixed storage


Removable storage


Data is stored using binary code (0 and 1).

Computer memory is measured in kilobytes.

Read Only Memory (ROM) is non-volatile because it cannot be changed.

Random Access Memory (RAM) is volatile because it only works when the computer is switched on.

There are three types of storage device: those that use magnetic media, others that use optical media, and those that use flash memory.

Different types of media have different storage capacities.

Storage devices can also be divided into those that are fixed and those that are removable.

Summary

Documents

Storage Devices