1. Backing storage media 1.Definition 2. Use of backing storage devices 3. Advantages and disadvantages

2. Without digital storage media like hard disks, cds, dvds, servers and so on, your computer will be just like a standalone video player, only processing digital signals and nothing more. These storage devices are non-volatile, meaning that they do not require constant power to store information. Thus they are most suitable for long term storage of information. On the opposite side are components like computer RAM where memory storage is dynamic but used only temporarily to aid processes. Most digital storage data devices are accessed sequentially, thus there will be seek time and latency to access any data on the devices. Of course there are other different kinds of storage devices, not just those that store your photos, music and other digital data. 3. Volatility Non-volatile memory Will retain the stored information even if it is not constantly supplied with electric power. It is suitable for long-term storage of information. Nowadays used for most of secondary, tertiary, and off-line storage. In 1950s and 1960s, it was also used for primary storage, in the form of magnetic core memory. Volatile memory Requires constant power to maintain the stored information. The fastest memory technologies of today are volatile ones (not a universal rule). Since primary storage is required to be very fast, it predominantly uses volatile memory. 4. Semiconductor-Electronic Semiconductor memory uses semiconductor-based integrated circuits to store information. A semiconductor memory chip may contain millions of tiny transistors or capacitors. Both volatile and non-volatile forms of semiconductor memory exist. In modern computers, primary storage almost exclusively consists of dynamic volatile semiconductor memory or dynamic random access memory. Since the turn of the century, a type of non-volatile semiconductor memory known as flash memory has steadily gained share as off-line storage for home computers. Non-volatile semiconductor memory is also used for secondary storage in various advanced electronic devices and specialized computers. 5. Electronic storage medium that uses low-power laser beams to record and retrieve digital (binary) data. In optical-storage technology, a laser beam encodes digital data onto an optical, or laser, disk in the form of tiny pits arranged in concentric tracks on the disks surface. A low-power laser scanner is used to read these pits, with variations in the intensity of reflected light from the pits being converted into electric signals. This technology is used in the compact disc, which records sound; in the CD-ROM (compact disc read-only memory), which can store text and images as well as sound; in WORM (write-once read-many), a type of disk that can be written on once and read any number of times; and in newer disks that are totally rewritable. Optical storage media 6. Magnetic storage media Magnetic storage uses different patterns of magnetization on a magnetically coated surface to store information. Magnetic storage is non-volatile. The information is accessed using one or more read/write heads which may contain one or more recording transducers. A read/write head only covers a part of the surface so that the head or medium or both must be moved relative to another in order to access data. In modern computers, magnetic storage will take these forms: Magnetic disk Floppy disk, used for off-line storage Hard disk, used for secondary storage Magnetic tape data storage, used for tertiary and off-line storage In early computers, magnetic storage was also used for primary storage in a form of magnetic drum, or core memory, core rope memory, thin film memory, twistor memory or bubble memory. Also unlike today, magnetic tape was often used for secondary storage. 7. 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. 8. Storage sizes Storage sizes 9. Read Only Memory (ROM) ROM is a special kind of 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 (see next page), the type of CPU being used etc. Because the data is 'read only', it can be read but not changed by the user. The ROM chip (although there may be more than one) is attached to the Motherboard. The key thing to remember about ROM is that the data is not erased when the computer is switched off - the data is stored permenantly. This type of memory is called 'non volatile memory' 10. Random Access Memory (RAM) 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 rebootrd 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'. As well as storing the data you are working on, RAM also stores the modules that are needed to make your applications work. For example, when you open up Microsoft Word, you may notice a short delay while the modules are loaded into RAM. 11. RAM is also needed so that you can have multiple windows open and so that you can switch between them. However, 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 1-2 Gb of RAM installed. 12. 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. 13. 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. It is possible to also have an external hard disk which can be plugged into the computer and used to back up your data and then stored in a different place to keep it safe. 14. 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. 15. 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 nowdays, 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. 16. 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 17. Zip Disks Zip disks are pretty much obselete 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 seperate plug in drive, which was an extra expense. They can store around 100Mb of data - 70 times more than a floppy disk. 18. Advantages Stores more data than a floppy disk Compresses data, reducing the file size, so more data can be stored Portable Disadvantages Almost obselete now Need a seperate zip drive to read the disk More expensive than floppy disks 19. 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. 20. 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 21. 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. 22. 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. 23. 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. 24. 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. 25. 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 26. 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 27. 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 28. Blu-ray Blu-ray Disc (also known as Blu-ray or BD) is an optical disc storage media format. Its main uses are high- definition video and data storage. The disc has the same dimensions as a standard DVD or CD. The name Blu-ray Disc is derived from the blue laser (violet coloured) used to read and write this type of disc. Because of its shorter wavelength (405 nm), substantially more data can be stored on a Blu-ray Disc than on the DVD format, which uses a red (650 nm) laser. A dual layer Blu-ray Disc can store 50 GB, almost six times the capacity of a double-dual layer DVD (or more than 10 times if single-layer).