Memory and storage

• Primary memory


  The part of a computer that stores data
• Data


  Units of information. In computing there can be different data types, including integers, characters and Boolean
• Programs


  Sequences of instructions for a computer
• Instruction

  A single action that can be performed by a computer processor
• Primary memory

  • It is built inside the computer
  • Data can be read from and written to primary memory extremely quickly
  • Gives the processor fast access to the data and instructions that the primary memory holds
• Types of primary memory

  • Read only memory (ROM)
  • Random access memory (RAM)
• ROM

  Read only memory. This is non-volatile memory or storage containing data that cannot be changed
• RAM

  Random access memory. This is volatile memory that is constantly being written to and read from. It does not retain its contents without a constant supply of power
• Non-volatile memory


  A form of computer memory that stores data even when not powered
• Volatile memory

  The memory used to store computer program data while it is being executed. RAM is the main type of volatile memory. It is volatile because when power is switched off it no longer retains any data
• Primary memory is comparatively limited in size, especially when compared with secondary storage
• In a modern personal computer, primary memory is often around 4 GB in size
• Primary memory


  The part of a computer that stores data
• Primary memory


  • Its contents are not lost when the computer is turned off
• Read only memory (ROM)

  Non-volatile memory or storage containing data that cannot be changed
• ROM can be read from, but not written to
• ROM

  Ideal for storing instructions and data that are needed for the computer to run
• Instructions and data in ROM are usually programmed by the computer's manufacturer and cannot be overwritten
• BIOS (Basic Input Output System)

  A program stored in ROM that runs as soon as the computer is switched on
• BIOS

  1. Checks that the hardware is functioning correctly

  2. Runs a second program known as the bootup or bootstrap program that loads the computer's operating system from the hard drive into the RAM
• The BIOS is always needed so it is stored in ROM
• Primary memory

  A key component of a computer system that holds data and programs currently in use
• Random access memory (RAM)

  • Volatile memory that is constantly being written to and read from
  • Does not retain its contents without a constant supply of power
  • When a computer is turned off, everything stored in its RAM is lost
• Volatile memory


  The memory used to store computer program data while it is being executed
• Data


  Units of information that can be acted on by instructions
• Instruction

  A single action that can be performed by a computer processor
• Operating system


  The software that manages the hardware and software resources in a computer system
• Program


  Sequences of instructions for a computer
• RAM

  • Can be read from and written to
  • The contents of RAM can be changed at any time, simply by overwriting them with other data and/or instructions
  • The more RAM a computer has, the more data and programs it can hold simultaneously
  • RAM can also be upgraded easily, unlike other types of primary memory
• How ROM differs from RAM

  ROM is read only and non-volatile, RAM can be read from and written to and is volatile
• Primary memory


  The part of a computer that stores data
• Primary memory

  • Holds data and programs that are currently in use
• Virtual memory


  A section of a computer storage drive which is temporarily used as RAM
• When the amount of RAM needed to hold all running programs and data is greater than the amount of RAM available

  Virtual memory is used
• Virtual memory

  1. Data in RAM and not currently being used is transferred to the hard disk

  2. Frees up room in RAM for other programs and data

  3. When the data on the hard disk is needed again, any other unused data is transferred to the hard disk before the original data is transferred back to RAM
• Using virtual memory makes a computer run slower, as the processor has to wait while data is swapped between hard disk and RAM
• As secondary storage devices have slower access times than RAM, the computer's processing performance can be severely impaired
• Processing performance can be improved

  By increasing the size of the RAM, thereby reducing the need for virtual memory
• Primary memory


  The part of a computer that stores data
• Primary memory

  • Holds data and programs that are currently in use
  • Is a key component of a computer system