STORAGE DEVICES

Name: ______

Class: _

Unless you want to lose all of the work you have done on your computer, you need to have a way to store it safely.

There are various types of storage devices, different devices are suitable for different tasks.

We will be looking at the main ones which you need to know about.

Storage Capacity

  • Data can be stored either in the 'internal memory' or on a 'storage device'.
  • The amount of data and instructions that can be stored is measured in 'bytes'.
  • One byte contains 8 bits (short for Binary Digit). This is the smallest unit of data that can be stored. Each 'bit' is represented as a binary number, either 1 or 0.
  • A single keyboard character such as the letter A or T takes one byte of storage.

We normally refer to the capacity of a storage device in terms of Kilobytes (KB), Megabytes (MB), Gigabytes (GB) - or even Terabytes.

Storage sizes /
Quantity / Information /
Bit / Smallest unit of data, either a 0 or 1
Byte / 8 bits
Kilobyte (Kb) / Assumed to be 1,000 bytes. In reality, it is really 1,024 bytes.
Megabyte (Mb) / 1,000 kilobytes (1,024 Kb)
Gigabyte (Gb) / 1,000 megabytes (1,024 Mb)

Hard Disk

The hard disk is the main storage device in your computer. It is a bit like a filing cabinet: all of your data files and applications software are stored on it.

The hard disk contains a number of metal platters which have been coated with a special magnetic material. The data is stored in this magnetic material. Thus, the hard disk is known as a magnetic storage device.

In order to access the data, the platters spin many thousands of times a second and a magnetic read and write head floats just above the surface of the platter.

When you hear the term 'hard disk crash', this refers to the read/write head crashing down onto the surface of the hard disk. There is a risk every time this happens that the data stored in the section just where the head crashes might be damaged. That is why it is a bad idea just to switch the computer off at the wall without shutting it down properly.

Hard disks are measured in Gigabytes. A typical hard disk size will be around 120 Gb - 1 Terabyte.

Advantages
  • necessary to support the way your computer works
  • large storage capacity
  • stores and retrieves data much faster than a floppy disk or CD/DVD
  • Stored items are not lost when you switch off the computer
  • Cheap on a cost per megabyte compared to other storage devices
Disadvantages
  • Far slower to access data than ROM or RAM chips
  • Hard disks can crash which stop the computer from working
  • Regular crashes can damage the surface of the disk, leading to loss of data in that sector
  • The disk is fixed inside the computer and cannot easily be transferred to another computer.

Floppy Disk

Floppy disks are one of the oldest types of portable storage devices still in use, having been around since the 1980s. However, they are gradually becoming obsolete and some manufacturers are now starting to build their PCs without floppy disk drives.

A floppy disk can store up to 1.44 Mb of data which is equivalent to around 300 pages of A4 text. They used to be the ideal storage device for transferring small files from home to work/school or from one office computer to another. But nowadays, many files contain graphics or WordArt and are larger than the size of the floppy disk.

Floppy disks are a magnetic storage device.

All disks must be formatted before data can be written to the disk. Formatting divides the disk up into sections or sectors onto which data files are stored. In the past, the user would have to format their own disks, but now they are sold pre-formatted.

Advantages
  • Portable - small and lightweight
  • Inexpensive
  • Useful for transferring small files between home and school
  • Security tab to stop data from being written over
  • Can be used many times
Disadvantages
  • Not very strong - easy to damage
  • Data can be erased if the disk comes into contact with a magnetic field
  • Quite slow to access and retrieve data when compared to a hard disk
  • Can transport viruses from one machine to another
  • Small storage capacity
  • Many new computers don't have floppy disk drives

Zip Disk

Zip disks are pretty much obsolete now. However, they were very popular as a backup medium before CD-RWs were developed and became cheap enough for everyone to use.

Zip disks look similar to a floppy disk but are a little bit thicker.

Computers generally didn't come with a zip drive installed, so you couldn't just use one in the same way as a floppy disk. You needed a separate plug in drive, which was an extra expense.

They can store around 100Mb of data - 70 times more than a floppy disk.

Advantages
  • Stores more data than a floppy disk
  • Compresses data, reducing the file size, so more data can be stored
  • Portable
Disadvantages
  • Almost obsolete now
  • Need a separate zip drive to read the disk
  • More expensive than floppy disks

Magnetic Tape

The amount of work that you do on your computer at home can easily be backed up onto a CD-RW or a memory stick. However, many organisations, such as your school or an office, need to back up large volumes of data each day. A CD-RW, DVD-RW or flash memory sticks just would not be large enough for doing this.

Large organisations who need to back up their systems daily tend to use magnetic tapes to store their data.

Magnetic tape uses 'serial access' to find a piece of data. It works in much the same way as a video tape that you might have at home. To find a specific piece of data, you have to start at the beginning of the tape and continue fast forwarding until you get to the piece of data that you need. This makes it fairly slow to find and retrieve data so it would not be much use to store data that you needed to get hold of quickly.

Advantages
  • relatively cheap per megabyte of storage
  • can store large amounts of data - over 100 Gb
  • can be set up to do the back up overnight or over the weekend
Disadvantages
  • serial access so can be quite slow to access data
  • need a special piece of equipment to record and read the data on the tape

Compact Disks (CD)

Compact Disks come in three main forms:

CD-ROM - CD Read Only Memory. This means that when you buy the disk, it already has the data or program stored on it. You can read it, but can't save to it. An example would be a music CD that you buy from a shop.

CD-WORM - CD Write Once Read Many. This means that you are able to save to this disk one time, so you can store your data or an application on it of your choice. However, once you have saved onto the disk once, you can access the data many times but can't save onto it again.

CD-RW - CD Read Write. This means that you can save data to your disk over and over again, just like you can with a floppy disk.

Compact disks are known as optical storage devices. Data is burned onto the surface of the disk using a laser beam in the CD drive. A laser beam is also used to read the data stored on the disk.

A typical CD can store around 650 Mb of data - equivalent to 450 floppy disks. The entire contents of four text based encyclopedias (no images) could be stored on a single CD.

Advantages
  • Small and portable
  • Very cheap to produce
  • Most computers can read CDs. If there is no CD drive, a DVD drive can usually read them
  • Fairly fast to access the data - quicker than a floppy disk or magnetic tape
Disadvantages
  • Fairly fragile, easy to snap or scratch
  • Smaller storage capacity than a hard drive or DVD
  • Slower to access than the hard disk.

Digital Versatile Disk (DVD)

DVDs are amongst the most common methods of copying and backing up data at home.

A DVD is similar to a CD in that it is an optical device and that a laser is used to store the data and read the data.

A single sided DVD can store about 4.7Gb of data. DVDs which store data on both sides can hold over 9Gb of data.

One problem with the DVD is that the different companies which make them haven't agreed on a standard format. Because of this, you will see various kinds of DVD disks for sale: DVD-R, DVD+R, DVD-RW and DVD+RW. You have to make sure that you buy the right kind of disk to go with your DVD equipment.

Advantages
  • Very large storage capacity
  • Sound and picture quality is excellent, making them ideal for storing films with video and sound.
  • DVDs are now mass produced so they are relatively cheap
  • DVD players can read CDs
Disadvantages
  • DVDs do not work in CD drives
  • There is no single standard of DVD
  • They can be easily damaged by breaking or scratching

Flash Memory

Flash memory storage devices are typically small, lightweight, removable and rewritable. They consist of a small printed circuit board which is encased in plastic or metal casing. They usually have a removable cap which covers and protects the part of the stick which is inserted into a USB port.

Memory sticks are available from 1 Gb up to 8 Gb.

Advantages
  • They are more compact and portable than floppy disks or CDs/DVDs.
  • They hold more data than a floppy disk and nowadays often more than a CD.
  • They are more reliable than a floppy disk because they have no moving parts
  • They are being developed with fashionable looking outer casings and are almost becoming a 'fashion accessory' much in the way of a mobile phone.
Disadvantages
  • At the moment, the cost per megabyte of storage is more expensive than floppy disks, CDs or DVDs.
  • They can be easily lost
  • The metal part which is inserted into the USB port can be snapped off if they are handled roughly

Year 11 ICT