Data Storage

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Data Storage

• Computing

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Primary Storage

• One of the fundamental properties of a computer
  is that it can store data.
• Primary storage is also known as memory.
• The CPU can directly access data stored in
  memory.
• Access to data in memory is very fast.

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Primary Storage

• There is a small amount of memory in the CPU
  itself.
• Data is stored in registers
• Each register holds a word of data (typically
  32 or 64 bits)
• Registers are the fastest forms of data storage.

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RAM Cache (Cache memory)

• RAM cache memory is a chip of memory commonly
  built into the motherboard.
• Speed is somewhere between super-fast registers
  and slower RAM.
• Used to speed up the processing.
• Stores frequently needed data.
• Smaller capacity than RAM, but larger capacity
  than registers

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RAM (Random Access Memory)

• RAM is connected to the CPU by an address bus and
  a data bus.
• Data access is slower than cache, but capacity
  is larger.
• RAM is volatile. The data is lost when the power
  is switched off.
• RAM is used for temporary storage of data and
  programs.
• Data can be changed.

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ROM (Read Only Memory)

• ROM is non-volatile The data is not lost when
  the power is switched off.
• Stored data can be read but not changed.
• ROM is used for permanent storage of data.
• Example The BIOS is stored on ROM. This is the
  program that boots up the computer.
• ROM memory chips are often found in embedded
  devices

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Secondary Storage

• Secondary storage is not directly accessible by
  the CPU.
• Data is input from and output to a storage
  device.
• Storage capacities are considerably larger than
  main memory.
• Access speeds are much slower than main memory.

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Comparative Speeds(Fastest first)

• Primary storage
• Registers
• RAM Cache
• Main memory (RAM)
• Secondary Storage

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Types of Secondary storage

• Magnetic Tape
• Magnetic Disk (Eg Hard Disk)
• Optical Disk (Eg CD, DVD)
• Flash Memory

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Magnetic Tape

• Large capacity - Tape cartridges can store
  hundreds of gigabytes of data.
• Inexpensive means of data storage.
• Slow access times.
• Commonly used for backup of data.

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Magnetic Disc

• Hard disks are the most commonly used secondary
  storage media.
• Data is stored on rotating platters of magnetic
  material and read by a swivelling arm.
• Relatively fast access speeds
• Sealed unit so durable.
• Some drives are external, so can be connected to
  different computers.
• 500 Gb drives are available.

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Optical Disks

• CDs and DVDs use laser technology to read/write
  data
• Low cost media
• Portable media
• External or internal drives are available.

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Flash Memory

• Used on memory cards and USB flash memory drives.
• Memory cards are used in digital cameras and
  mobile phones
• Flash memory drives can be connected to a USB
  port of a computer.
• Portable