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 * Secondary storage ## Prim...

# 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 in 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 commonly used secondary storage devices are magnetic disks, optical disks, flash memory, USB drives and, less frequently magnetic tapes.