1. Storage Devices

2. 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. Introduction

3. 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'. Storage Capacity Storage sizes QuantityInformation BitSmallest unit of data, either a 0 or 1 Byte8 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)

4. ROM & RAM The Primary Storage (main memory) of a computer is made up of a set of memory chips called ROM and RAM ROM = R ead O nly M emory, which store things permanently and can never be changed. RAM = R andom A ccess M emory, which is only usable when the power to the computer is switched on.

5. ROM is a memory which stores the instructions which the computer uses when it 'boots up' - the BIOS (basic input output system). It allows it to check the type of hard disk installed, the amount of RAM installed, the type of CPU being used etc. Because the data is 'read only', it can be read but not changed by the user. The key thing to remember about ROM is that the data is not erased when the computer is switched off - the data is stored permanently. This type of memory is called 'non volatile memory' ROM – READ ONLY MEMORY

6. How many times have you worked for a whole lesson on something, which you were just about to save but then the computer crashed or your mate 'accidentally' switched it off. When you reboot and logged back in, your work was gone forever. This was because your work was stored in RAM, or 'temporary memory'. It was fairly safe there while the computer was working, but as soon as it was switched off, everything disappeared. This type of memory known as 'volatile memory'. Random Access Memory (RAM)

7. If you have a lot of windows, documents and different applications running, you might find that your system starts to slow down. This is because your RAM is full up and it is having to decide what it needs to keep stored in memory at any given time and what it can release. If this happens to you a lot, you can improve the performance of your computer by installing extra RAM. Most computers are typically sold with 512Mb - 1Gb of RAM installed. Random Access Memory (RAM)

8. ROM RAM Read Only Memory Random Access Memory The instructions to start the computer are stored on this.BIOS Programs and data stored on RAM are lost when a computer is switched off. This memory is volatile memory This sort of memory is non-volatile memory

9. Secondary Storage

10. Magnetic disks

11. The hard disk 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. Hard Disk

12. 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. The term 'hard disk crash', this refers to the read/write head crashing down onto the surface of the hard disk. A typical hard disk size will be around 120 Gb - 1 Terabyte. You can have an external hard disk used to back up your data and then stored in a different place to keep it safe. Hard Disk

13. Advantages 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. Hard Disk

14. Floppy disks are one of the oldest types of portable storage devices still in use, since the 1980s. A floppy disk can store up to 1.44 Mb of data 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. 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. Floppy Disk

15. 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 Floppy Disk

16. Many organizations, 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 organizations 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. Magnetic Tape

17. 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 Magnetic Tape

18. 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. Compact Disks (CD)

19. 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 (CD)

20. 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. Compact Disks (CD)

21. 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. Digital Versatile Disk (DVD)

22. 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 Digital Versatile Disk (DVD)

23. 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. Flash Memory

24. 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 Flash Memory

25. 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. Zip Disks

26. 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 Zip Disks