Memory (1.2)

Memory (1.2)

1. RAM VS ROM.

   • RAM - Random Access Memory, ROM - Read Only Memory.
   • When a computer boots up:
     • ROM contains all the instructions a computer needs to properly boot up, these instructions are called BIOS.
       • BIOS -- Basic Input Output systems.
     • The operating system is copied from secondary storage to RAM.
     • As soon as the computer is on, the CPU reads the instructions from the ROM, this tells the CPU to preform self checks and set up the computer.
       • eg. Test memory to make sure it is functioning properly, see what hardware is present and copy the operating system into RAM.
   • Types of memory:
     • RAM is volatile whereas ROM is Non-volatile.
       • Volatile -- Temporary storage, requires power to retain data. Non-volatile -- Permanent storage, doesn't require power and keeps contents when power is not present.
     • ROM can only be read not written to. RAM can be read and written to.
   • When software applications, documents or files are opened they are copied from secondary storage to RAM and stay in RAM until closed.
   • RAM is slower than the CPU cache but faster than secondary storage.

2. Virtual Memory.

   • Computers have limited RAM, as applications are opened RAM fills with data, when RAM is full, the computer needs somewhere else to put application data.
     • The computer moves data that hasn't been recently used to a location on secondary storage known as virtual memory.
   • May be needed if there are too many applications open at once, or if a particularly memory-intensive application is being used.
   • When the CPU needs to read data that is being stored in virtual memory, it must move the data back to the RAM.
   • Using Virtual Memory can make a computer slow to respond when switching between applications, or when using a memory-intensive application.

3. Flash memory.

   • A common type of non-Volatile memory that stores data in electrical circuits by trapping electrons, its used in SD cards, USB sticks and Solid State Drives.
   • Magnetic Hard Disks
     • The traditional storage in PC's and laptops, its made up of a stack of magnetised metal disks spinning at a rate of between 5400 and 15000 rpm.
     • Data is stored magnetically in small areas called sectors within circular tacks, read/write heads on a moving arm are used to access sectors on the disks.
     • Portable HDDs are popular for backing up and transporting large amounts of data.
     • Despite their moving parts, they are generally long lasting and reliable although they could be damaged by large impacts being dropped.
   • Solid State Drives
     • Storage devices with no-moving parts, most of them use a type of flash memory, they are used for the same purpose as HDDs- for internal storage.
     • SSDs have significantly faster read/write times than HDDs, this can give much quicker times for booting up and opening programs and files.
     • Like HDDs, portable SSDs can be used to back up and transport data.