Memory

• Two types of memory used as primary storage:

  • RAM (Random Access Memory).
  • ROM (Read Only Memory).
• RAM stores programs or data that are running or open.
• RAM is directly accessed by the CPU.
• RAM is volatile: when your computer is turned off, data stored there is lost.
• All programs and data are stored permanently on the hard drive.
• When the computer is first turned on, no data is stored in RAM.
• When the computer is first turned on, it loads the operating system from the hard drive into RAM.
• When applications or programs are loaded, they are copied into RAM from the hard drive. Documents and files (data) that are used by those programs are also opened by copying them into RAM.
• Virtual memory is part of the hard drive used as an extension to RAM.
• A page of data is a fixed-length block of virtual memory.
• When pages of data are moved between RAM and the hard disk this is known as swapping or paging.
• Advantages of virtual memory:

  • Uses cheap secondary storage on the hard drive.
  • Prevents error messages saying 'out of memory' - the programs and files will still open.
• Disadvantages of virtual memory:

  • Accessing virtual memory is very slow.
  • To access data, the existing data in RAM needs to be copied to the virtual memory, then data in virtual memory needs to be copied into RAM.
• Read-Only Memory (ROM) is used to store data that needs to be permanently held in primary storage, even when a computer has no power.
• Data is read from ROM, but cannot be written to it.
• ROM is non-volatile as the data isn't lost if the power is off.
• ROM is used to store:

  • The bootstrap.
  • The BIOS.
• Bootstrap is the initial program that is run when the computer is turned on. It tells the computer where it will find the operating system on the hard drive.
• The Basic Input/ Output System (BIOS) controls the basic technical configuration of the computer such as the processor speed and system time.
• The BIOS can run without a hard drive or other secondary storage being present.
• RAM vs ROM differences:

  A) 4 GB to 32 GB

  B) Running programs and operating system

  C) Yes

  D) Yes

  E) Yes

  F) 4 MB to 8 MB

  G) BIOS and bootstrap

  H) Yes

  I) No

  J) No

  
• The speed that data can be accessed changes through the different components in a computer.
• Components in a computer: from quickest access speed to slowest.

  1. Processor.
  2. Cache.
  3. Primary Memory. RAM/ROM.
  4. Virtual memory (on hard drive).
• The CPU interprets, processes and executes instructions, most often from the hardware and software programs running on the device.