Topic 3

• Types of primary storage:

  • In the Von Neumann architecture, primary storage is needed to store programs that are currently running and need to be accessed by the CPU
  • The two types used as primary storage are RAM (Random Access Memory) and ROM (Read Only Memory)
• RAM:

  • Often referred to as main memory, primary memory, primary storage
  • Can be read from and written to
  • Access to RAM is much faster than a hard drive
  • Named Random Access Memory due to the CPU's ability to access any part of the memory in the same amount of time
  • Normally stores the operating system, software currently in use, and the data which the software is using
• RAM:

  • Stores running programs and data when the computer is turned on
  • Data stored in RAM is lost when the computer is turned off
  • Volatile as it loses data if the power is off
  • All programs and data are stored permanently on the hard drive, known as non-volatile storage
• RAM:

  • When the computer is first turned on, no data is stored in RAM
  • The operating system is loaded from the hard drive into RAM
• RAM:

  • When applications or programs are loaded, they are copied into RAM from the hard drive
  • Documents and files (data) used with those programs are also opened by copying them into RAM
  • RAM starts to fill up as programs, documents, and files are copied
• Virtual memory:

  • Part of the hard drive used as an extension to RAM
  • Advantages: uses cheap secondary storage, prevents 'out of memory' error messages
  • Disadvantages: accessing virtual memory is slow, data in RAM needs to be copied to virtual memory and vice versa
• Read-only memory (ROM):

  • Used to store data permanently even when the computer has no power
  • Data is read from ROM but cannot be written to it
  • Non-volatile as data isn't lost if the power is off
• ROM:

  • Used in modern computers to store the initial program run when the computer is turned on (bootstrap) and the Basic Input/Output System (BIOS)
  • BIOS controls basic technical configuration of the computer such as processor speed and system time
• RAM vs ROM differences:

  Characteristic:

  • RAM: Typically 4 GB – 32 GB
  • ROM: Typically 4 MB – 8 MB

  Used to store:

  • RAM: Running programs and operating system
  • ROM: BIOS and bootstrap

  Read ability: Yes for both

  Write ability: Yes for RAM, No for ROM

  Volatile: Yes for RAM, No for ROM
• Memory speed:

  • The speed that data can be accessed changes through the different components in a computer
  • Slower components are cheaper for each byte of data stored