Primary and Secondary Storage PDF

Primary and secondary storage All computers need to store and retrieve data for processing. Storage refers to the media and devices used to keep data and instructions available for immediate or later use. Storage can be grouped into two categories: ❖ Primary storage ❖ Seconda...

Primary and secondary storage All computers need to store and retrieve data for processing. Storage refers to the media and devices used to keep data and instructions available for immediate or later use. Storage can be grouped into two categories: ❖ Primary storage ❖ Secondary storage Primary storage As you learned with IT Book 1, processing takes place the central processing unit (CPU). The CPU consists of two units, which are the control unit (CU) and the arithmetic and logic unit (ALU). The CPU takes raw data and, following a set of instructions (programs), converts it into information. As the main part of the CPU, the control unit (CU) directs and coordinates all the activities within it. The arithmetic and logic unit (ALU) performs all the arithmetic and logic functions in a computer. Primary storage, which is directly accessible to the CPU, holds data and instructions that the computer is processing at the time. Primary storage is also called main memory or immediate access store (IMAS). This type of storage consists of a group of memory chips positioned on the motherboard (main circuit board) of the computer. These chips are located here because the processing unit can only act on data and instructions that are held in primary storage. Primary storage consists of two types of memory chips: ❖ Random- access memory (RAM) ❖ Read-only memory (ROM) chips Random-access memory (RAM) Random access memory (RAM) is only filled after a computer is turned on and give it something to do. RAM is available to the processor immediately and holds data and instructions temporarily, while processing takes place. It also holds data that results from processing which is waiting to be output or stored in secondary storage device. Therefore, RAM is also called working memory. Programs and data in secondary storage must first be loaded in RAM before they can be processed. For example, before a letter can be typed, or data entered for a spreadsheet, this CPU must first load the application programs, such as a word processing or spreadsheet program, into memory. These application programs, as well as using any of the applications are held in RAM until the application is closed or the power is turned off. As ram is volatile if these inputs are not stored on the secondary storage device will be lost. The time Vito means that if the power is turned off or the computer is rebooted information that is held in RAM will be lost. RAM chips have limited storage capacity. In 2019 a professional computer ram storage capacity can vary from 4 GB to 32 GB. RAM is also expensive and is a major factor in the final price of a computer. Read-only memory (ROM) Read only memory chips for the data and instructions necessary for starting up the computer when it's switched on. ROM is commonly used to store system level programs such as the BIOS program. ROM chips may also hold translators for high level languages and operating systems. These instructions are fixed at the time of manufacture and are sometimes described as being hard-wired. This ensures that the instructions that are stored in ROM and always there, regardless of whether the power is on. Therefore, ROM is nonvolatile. This is necessary because when the computer is first turned on, the system memory is empty and needs the instructions stored in ROM for the PC to boot up. Variations of ROM chips, namely, programmable ROM (PROM) and erasable programmable ROM (ERPOM), which allow some flexibility in storing data and instructions, are also available. PROM chips can be programmed using special equipment and they can also be written to, but only once. EPROM is a ROM that can be deleted and reprogrammed. Secondary Storage Secondary Storage is also called auxiliary or backup storage. This type of storage is used to store data and instructions when they are not being processed. Secondary storage is more permanent than main memory, as data and instructions are ‘remembered’ when the power is turned off. Secondary storage is also much cheaper than primary storage and is unlimited The most used secondary storage devices are magnetic disks, optical disks, flash memory, USB drives and, less frequently, magnetic tapes. Magnetic disks Magnetic disks are one of the most widely used secondary storage mediums for computers. Magnetic disk provide direct access to the store data. This means that you can go directly to specific piece of data without having to access any other data either before or after the data you want. The capacity access speeds of magnetic disks vary with each device or medium. Types of magnetic disks include diskettes (which are now almost obsolete) and hard disks Hard Disks Hard disks, as the name suggests. are thin, rigid (unbending) disks made of highly polished metal. The surface of each side of a disk (also called a platter) is covered with a substance that can be magnetized. This allows data to be stored on both sides of the disk as magnetized or unmagnetized spots. The disks constantly rotate at a high speed and may have one read or write head per disk (a moveable head) or, on more expensive disks, every track in each disk may have its own read or write head (fixed head). As each track on a fixed head disk drive has a read or write head, less time is taken to access data and instructions, as the seek time is removed. Almost all PC’s I have a hard drive holes inside the system unit and attached to the motherboard by a special cable. These hard drives are not renewable and vary in storage capacity from 500 GB to 8 TB or more. The hard drive music stores application software, such as word processor database, spreadsheet, and so on and the operating system. Two additional types of hard drives that can be used with a PC are: ❖ External hard drives ❖ Removeable hard disk packs External hard drives External hard drives can be used if there is no space in the system unit to house another hard drives. They have their own power source, and they connect to the system unit through a USB port. External hard drives are easy to remove and connect to another computer, which makes them portable. External hard drives are available in various sizes that range from 1TB to 8 TB. A typical example of external hard drive is the Seagate 8TB Innov8. Removable hard disk pack Remove the hard disk type because Tabitha tween 6 and 20 hard disks lined up on one above the other in a sealed unit. The storage capacity is usually very large and can range from 1TB to 10TB or more. Fixed disk drives Disk drives are similar to those phone and PC's. These have a large storage capacity and are more reliable than removable hard disks. A mainframe computer may have between 20 and 100 fix disks house in a single cabinet. Data is transmitted to the CPU using a single data path. A RAID storage system The term ‘RAID’ stands for a redundant array of independent disks. A RAID storage system consists of a cabinet that contains many disk drives (up 100 drives). Besides holding more data than a fixed disk this storage systems does multiple copies of data on different drives. OneDrive all the others can take over which allows the data to be recovered. Data is transmitted to the CPU using multiple data paths. Optical Disks Optical discs are red by laser lights that this are men of a type of plastic polycarbonate. The data is stored in our layer inside the plastic. A metal coating usually aluminum reflects the laser light back to our sensor the main types of optical disks are CD's DVD CD Three types of CD's are CD-ROM cd-r and CD RW CD-ROM (compact disk) CD-ROM stands for compact disc read only memory. This means that you can only read what is on the disk but cannot add or change anything the data is encoded and read optically with a low intensity laser light. The data is represented as a series of pits and lands. A pit is a little depression formed by the laser burning into the data layer. Is land is the path between the pits or the smooth surface. Reading a CD is done by shining a laser light at the disk and detecting changing reflecting patterns. The laser beam reflecting off the smooth surface a land is interpreted as 1 bit. There is no reflection when the laser beam enters a pit which is interpreted as a 0 bit The speed at which that data is accessed depends on how fast the disk spins the faster the disk spins the faster the data can be transferred to the computer's memory the speed of acid ram drive is shown by a number followed by an X. Typically CD-ROM drive speeds are 48 X 50X and so on. The higher the number the faster the disk spins which results in faster data access due to the large storage capacity up to 800 megabytes CD-ROMs are used to store software packages for sale or distribution. They are particularly useful for storing multimedia as well as application software packages such as encyclopedias word processors training programs and games and graphics packages. CD-R Stands for compact disc recordable. The disk allows you to write data onto it only once using a CD recorder or burner. The disk then becomes as CD-ROM as its contents cannot be changed. As CDR is ideal for storage of large data that do not change frequently. CD-RW The CD-RW stands for compact disc rewritable. CD RW I know a common choice for use as backup storage. The data layer of these disks uses a phrase changing mental allow film. By using a higher intensity laser light this film can be melted to the level out the marks made by the laser What she needs the previously stored data. New data can then be recorded using a lower intensity laser light to bum the new data. In theory you can erase and write on these disks As many as 1000 times. Therefore, CD-RW is an ideal backup storage device for storing large volumes of data that changes frequency. DVDs The Tom DVD starts with digital versatile disk. The main types DVD ROM DVD R and DVD RW. They look similar to a CD-R disc but can hold much more information a typical DVD can hold between 4.7 gigabytes and 17 gigabytes of information DVDs are used mainly for storing videos of film as the quality of sound and video output is far superior to video clips. Bit Byte= 8 bits Kilobyte= 1,024 bytes Megabyte= 1,024 kilobytes Gigabyte= 1,024 megabytes Terabyte= 1,024 gigabytes Petabyte = 1,024 terabytes Exabyte= 1,024 petabytes Zettabyte= 1,024 exabytes Yottabyte= 1,024 zettabytes