Backing storage and Memory Year 9 - ICT Notes

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1 Backing storage and Memory Year 9 - ICT Notes Storage and Memory Storage Also called as backing storage/secondary storage Examples of storage media are Hard disks Optical disks( CD, DVD, Blu-ray) Flash memory devices Magnetic tapes Memory Also called as primary/main memory Types of memory RAM and ROM Page 1 of 20

2 Storage devices and media The storage medium is the actual material object used for storing the data. The storage device is the item of equipment that handles the use of the medium. Examples of storage medium: Hard disks Optical disks( CD, DVD, Blu-ray) Flash memory devices Magnetic tapes Examples of storage devices: Hard disk drives(hdd) Solid state drives(sdd) Optical disk drives( CD drive, DVD drive) Flash memory drives Page 2 of 20

3 Types of access (Random/Direct Access and Serial Access) Random/Direct Access The computer can calculate exactly where the data has been stored and can go straight to it directly (instant access). The computer knows where all of the data on the storage medium is and so it can access it very quickly. This direct method of accessing data is much faster than serial access. This method is used with: Hard disk drives CD s and DVD s USB memory sticks Flash memory Blu-ray discs Direct access is used in situations where fast access to data is important like in online booking systems and Point-of-sale (POS) terminals in shops. Serial Access Data is accessed by starting at the beginning and then searched through, in order/sequence, until the required information is found. The need to search from the beginning of the storage medium makes this type of data access very slow. This method is used with: Video cassettes Music cassettes Backup tape cartridges( hold lots of tape for backing up large amounts of data) Magnetic tapes still used for backing up large amounts of data/overnight backup/ server or network backup in organizations like schools and business. Serial access medium like magnetic tapes are also used in batch processing systems like payroll and in the preparation of utility bills. The way that serial access works means that all of the data has to be read and there is no danger of missing out someone s wage payment or bill invoice. Page 3 of 20

4 Examples of Magnetic Storage Media Hard disks Hard disks can store as very large amount of data. The main storage area in a desktop computer system is the hard drive. Access to the data on a hard disk is very fast. On a hard disk, the data is stored on multiple disks or platters, held vertically above each other (see Figure). On each individual disk, the data is stored in concentric tracks. For every track of data, there are corresponding tracks above and below it. For instance, the fifth track on the first surface is directly above the fifth track of the second surface, and below that is the fifth track of the third surface. The corresponding tracks form a cylinder. The number of cylinders is equal in number to the tracks on each surface of the disk. For each surface ( usually at the top and bottom of each platter) there is a read/write head, set on the tip of a small arm. These heads move in step with each other, traversing in and out over the spinning disk. Access time To reach the correct spot on the disk for reading or writing data, the head must move to the correct track. Meanwhile, the hard disk spins, maintaining a constant speed. The byte to be assessed arrives under the head as the disk turns. On average, it takes half a rotation for the correct byte to reach the head s position. Page 4 of 20

5 The total access time on average is then: Time for head movement to reach track + Time for half a complete rotation If the drive needs to access bytes that directly follow each other on a single track, no further head movement is needed because the head can remain on the same track. Moreover, if the bytes follow each other, it takes very little time for each consecutive byte to arrive beneath the head. So the average access time per byte is far less if a stream of consecutive bytes is being read than it is for one-off access. Fixed heads and moving heads Some types of hard disk have a read/write head permanently stationed above each track of the disk. Each surface has many fixed heads instead of a single moving head per surface. This means that no time is needed to reach the correct track; the respective heads are already in place, so access is much faster on average, the time for a half rotation. RAID (Redundant Array of Inexpensive Drives) This storage device essentially carries multiple copies of data, on different hard disk drives. If one fails, the data can still be recovered from the others. Advantages and disadvantages of Magnetic Storage Media Page 5 of 20

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7 Examples of Optical Media Uses of CD-ROMs and DVD-ROMs: CD-ROMs are used by manufactures to store smaller files such as: Music tracks Software( such as word processors, spreadsheets etc) DVD-ROMs have much larger storage capacities than CD-ROMS and are used to store bigger files such as: Movies Modern games Multimedia encyclopedias Page 7 of 20

8 Uses of CD-R and DVD-R: CD-R s used to create personalized playlists of music. DVD-R s used to store home recordings of video shot on digital cameras. They can be used to backup important data so that there are copies in case the originals get erased or deleted. They can be used to transfer data from one computer to another. Uses of CD-RW and DVD-RW: CD-RW s are used to create personalized playlists of music and then add/remove songs as you wish. DVD-RW s are used to record television programmes and can be recorded over many times. They can both also be used to make backups of computer files. Page 8 of 20

9 Uses of DVD-RAM: Because DVD-RAM discs last so long they are used in video and data archiving (safe store for important files and records). Used in DVD recorders to record TV programmes (on digital and satellite) to allow simultaneous recording and playback. Used in camcorders to store video (Reliable for many years). Uses of Blu-ray Discs: Used to store high definition video (high quality movies). Used in some home video consoles (like playstation 3). Used to back up hard disk drives in PC s. Page 9 of 20

10 Examples of Solid State Media An SSD (solid-state drive or solid-state disk) is a nonvolatile storage device that stores persistent data on solid-state flash memory. Solid-state drives actually aren't hard drives in the traditional sense of the term, as there are no moving parts involved. Like a memory stick, there are no moving parts to an SSD. Rather, information is stored in microchips. Conversely, a hard disk drive uses a mechanical arm with a read/write head to move around and read information from the right location on a storage platter. This difference is what makes SSD so much faster. This is memory based on silicon technology rather than magnetic or optical technology. It has no moving parts and is very fast compared to other memory methods. Silicon memory 'chips' are often mounted together to form a memory card. Solid state memory includes RAM, ROM, EPROM, EEPROM and Flash Uses of Solid state Hard Drives: Used in desktop PC s and laptops to permanently store data such as: Operating systems Software applications ( such as word processors, spreadsheets etc) Music/Video files School work, photos Page 10 of 20

11 Property Notes Type of storage Data Access Cost of storage Capacity Speed Portability Durability Reliability Solid state Direct access More expensive per byte of storage than hard disk, magnetic tape, CDs and DVDs 2 gigabyte upwards As an external storage device, it is slower than an internal hard disk. It is faster than Magnetic tape, CDs and DVDs. If it is used as internal storage, it then becomes faster than an internal hard disk. Very portable as it is designed to fit into Small electronic devices. Very durable. Resistant to pressure, temperature extremes and accidental damage. It has a limited number of read/write cycles which limits its useful life. Usually very reliable Page 11 of 20

12 Flash Memory / Solid State Memory Flash memory is a non-volatile, solid state storage device. (i.e. keeps its data without power and has no moving parts). Flash memory is increasingly being used in a wide range of devices. Some examples include: Small, lightweight USB memory sticks, available for many Gigabytes. Memory cards for digital cameras. Main internal storage for tablet computers (SSD). Digital audio players. Mobile phones. Video game hardware. Flash memory offers very fast access to data and programs. However, retrieving data from an external flash memory device such as a USB stick would be slower than an internal hard disk because the speed of access is restricted by the USB link or connection. With the development of tablet computers, flash memory is used as the main form of internal storage because there is no room for a traditional hard disk. These disks are called SSD (solid state storage). In this case, access to the data stored in flash memory would be much faster than from a hard disk because there are no moving parts involved. Currently, the down side to using flash memory as the main storage method is that it has a limited number of read/write cycles which limits its useful life span. Flash memory, when packaged in a "memory card", is very resilient to damage, unlike many other storage devices. It can withstand extremes of temperature, being immersed in water or being accidentally dropped. Page 12 of 20

13 Memory Sticks/Pen Drives Memory sticks are small, portable external storage devices. They are used to easily transfer data between computers. Memory sticks use solid state technology and are usually connected to the computer via USB ports. Data access and transfer is very fast. Memory sticks are very cheap to buy. Uses of Memory Sticks: Used for easily transporting files/data between computers. Used for backing up data quickly and easily. Flash Memory Cards Flash memory cards are also known as Secure Digital Cards (or SD Cards). SD cards are small and rectangular in shape. These are a form of EEPROM (Electronically Erasable Programmable Read Only Memory). Page 13 of 20

14 SD cards use solid state technology ( they have no moving parts). A wide range of devices have slots to read flash memory cards including laptops, mobile phones, tablets and mp3 players. SD card readers can be used to transfer data from the cards onto a desktop PC. Uses of Flash Memory Cards: SD cards are used to store photos on digital cameras. SD cards are used in hand held devices( like PDA s and Palmtop s) to store files and data. Micro SD cards are used in mobile phones as memory cards to store photos and music etc. Micro SD cards can be used by MP3 players to store music files Page 14 of 20

15 Internal and External Storage Some storage devices are classed as 'internal' which means they are inside the computer case. Most computers have some form of internal storage. The most common type of internal storage is the hard disk. to hold the operating system so that the computer is able to access the input and output devices. to store the applications software that you use and more than likely, the original copies of your data files. Internal storage allows the data and applications to be loaded very rapidly into memory, ready for use. The data can be accessed much faster than data which is stored on an external storage device. This is because internal storage devices are connected directly to the motherboard and its data bus whereas external devices are connected through a hardware interface such as USB, which means they are considerably slower to access. The main disadvantage of internal storage is that when the hard disk fails (and it will), all the data and applications may be lost. This can be avoided to some extent by using more than one hard disk within the machine. Each hard disk has a copy of all the data, so if one fails the other can carry on. This is called a RAID array. An alternative is to use external drives for backup. External drives are connected to the computer with a cable plugged into a suitable interface such as an USB port. Data then passes back and forth across the interface. The main advantage of external drives is that they are portable and so data is easily moved from one location to another. also allow safe backup of internally stored data. The main disadvantage compared to an internal drive is data transfer is slower and they also take up space around the computer. Constant plugging in and out can also physically wear out the port over time. External storage takes many forms, for example: Page 15 of 20

16 portable hard disks magnetic tape memory stick / flash drive solid state memory cards DVD or CDs Each type of external storage has to have the correct interface on the computer in order to connect. Addresses and Locations Memory is divided into many different locations, each of which can store one byte. The computer can find a specific location in memory using its address, which is a unique number referring to that location. Having addressed a particular location in memory, the computer can read or change its contents. Words, bits and bytes A word is the amount of data that a computer can directly access at one time. Different computers can access one, two, four or more bytes of data at one time. Storage Capacity Storage capacity is the term given to the maximum amount of data that can be stored on the media. The computer will store your work as a file. The size of the file depends on the amount of data in it, storage amounts are measured in bytes and there are 8 bits in 1 byte. A byte can store one character of data. (1 Character = 1 byte) Bits are short for binary digits. 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 letter on a keyboard takes up 1 byte of storage (8 bits). For example, if the computer reads four bytes at once then its word length is 32 bits. Page 16 of 20

17 Storage Capacity Units: We refer to the storage capacities of different media in the following units: Unit Abbreviation Information Bit Smallest unit of data(either 0 or 1) Byte 1 byte=8 bits Kilobyte KB 1 KB= 1000 bytes Megabyte MB 1MB= 1000 Kilobytes Gigabyte GB 1 GB= 1000 Megabytes Terabyte TB 1 TB=1000 Gigabytes Backups A backup is a copy of a file. You should back up all your files regularly so that you always have up-to-date copies of all your work. A backup is more secure if it is stored separately from the computer. Reasons for keeping backups: Accidental damage: Data may be accidently overwritten/erased/corrupted Deliberate damage: Malware/viruses may damage the data System/hardware failure or damage Physical problems e.g. data may be lost due to fire/flood/computer theft Factors to be considered while backup: Media/device ( determined by total file size) Where to keep the backup e.g. away from computer Can it be stored securely e.g. encryption/passwords What files to back up e.g. find/select How often to make a backup Can it be automated Who has access to backup/ how many copies should be kept When to run backup Page 17 of 20

18 File Compression If you start storing pictures and graphics you could use several DVDs or you could compress your files. If you kept backups in this way, if a file became lost or corrupted you could recover it by looking for a copy on the external portable hard disk, and then on the most recent DVD. If you could not find a good copy then you would work back through the DVDs until you found one. If the backup file was compressed you would have to decompress it before you could use it. File compression is making the file size smaller so that we could save storage space and upload, download and attach files faster. When decompressing a picture or graphics, it would lose its quality. Memory RAM (Random Access Memory) RAM is used to temporarily store information that is currently in use by the computer. This can include anything from word documents to videos RAM can be read from and written to and so the information stored in RAM can change all the time. RAM is a fast memory. Data can be written to and read from RAM very quickly. RAM is generally measured in GB (Gigabytes). RAM is volatile memory. This means that information stored in RAM is deleted as soon as the computer is turned off. The more RAM you have installed in your computer the faster it can perform. You can open and use more programs at the same time without slowing the computer down. ROM (Read Only Memory) ROM is used to permanently store instructions that tell the computer how to boot( start up). It also loads the operating system ( e.g. Windows). These instructions are known as the BIOS (Basic Input/output system) or the boot program. Information stored in ROM is known as READ ONLY. This means that the contents of ROM cannot be altered or added to by the user. Page 18 of 20

19 ROM is fast memory. Data stored in ROM can be accessed and read very quickly. ROM is non-volatile memory. This means that stored information is not lost when the computer loses power. Other examples of ROM include: DVD/CD ROMs bought in stores containing pre-recorded music and movie files. These are played back at home but cannot be altered. ROM in printers which is used to store different font types. The term immediate-access store (IAS) means the memory immediately available to the CPU which includes both RAM and ROM. Types of ROM Programmable read-only memory (PROM) has no data locked into it when first manufactured. But later, a company using PROM chips to make a computer can put in its own information. The data would then be locked in place, so the memory can no longer be changed. Erasable programmable read-only memory (EPROM) gets its original data in the same way as PROM does. But, if necessary, the data can be erased using a special light shining on a window on the chip, or by using a special electric charge (electrically erasable programmable read-only memory - EEPROM). This means that the data can be used in read-only mode, but that the memory can also be reset as required. Page 19 of 20

20 Processor (CPU / Central Processing Unit) Functions of CPU The Central Processing Unit (CPU) is the brain of the computer. The CPU controls what the computer does and is responsible for performing calculations and data processing. It also handles the movement of data to and from system memory. CPU s come in a variety of speeds which are known as clock rates. Clock rates are measured in Hertz. Generally, the faster the clock rate, the faster the performance of the computer. The central processing unit (CPU) of a computer carries out the instructions of a computer program. It performs the basic arithmetical, logical, and input/output operations of a computer system. The CPU is like the brains of the computer - it typically refers to the CPU as the processor. Components of CPU A typical CPU has a number of components. The first is the arithmetic logic unit (ALU), which performs simple arithmetic and logical operations. Second is the control unit (CU), which manages the various components of the computer. It reads and interprets instructions from memory and transforms them into a series of signals to activate other parts of the computer. The control unit calls upon the arithmetic logic unit to perform the necessary calculations. Third is the cache, which serves as high-speed memory where instructions can be copied to and retrieved. Early CPUs consisted of many separate components, but since the 1970s, they have been constructed as a single integrated unit called a microprocessor. Processor speed Processor speed measures (in megahertz or gigahertz; MHz or GHz) the number of instructions per second the computer executes. CPU clock speed, or clock rate, is measured in Hertz generally in gigahertz, or GHz. A CPU s clock speed rate is a measure of how many clock cycles a CPU can perform per second. For example, a CPU with a clock rate of 1.8 GHz can perform 1,800,000,000 clock cycles per second. **************************************************************************************************** Page 20 of 20