Storage Devices Notes

Storage Devices Overview

  • A storage device is any computing hardware used for storing data files and information. It can hold and store information both temporarily and permanently, and can be internal or external to a computer.
  • Storage devices can be used to store data while the system is running (temporary) or for long-term storage (permanent).

Primary Storage

  • Primary storage devices are also known as main storage or memory.
  • They are the area in a computer in which data is stored for quick access by the processor.
  • Typically, primary storage contains an instance of all data and applications currently in use or being processed.

Primary Storage Types

  • There are two main types of Primary Storage Devices:
    • RAM (Random Access Memory)
    • ROM (Read Only Memory)

RAM (Random Access Memory)

  • RAM stores data temporarily in the computer.
  • Also known as Main Memory & Random Access Memory.
  • Can contain operating instructions, loose data, or content from programs that are running.
  • When the computer is switched off, all data in RAM is cleared.
  • RAM is volatile memory.

ROM (Read Only Memory)

  • When a computer is switched on, the BIOS (Basic Input/Output System) and basic hardware instructions are loaded from ROM.
  • ROM contains the programming that allows the computer to be “Booted Up”.
  • This type of memory is non-volatile because it retains data when power is removed.

Secondary Storage

  • Secondary Storage is non-volatile memory (does not lose stored data when the device is powered down).
  • It is not directly accessible by the CPU because it is not accessed via the input/output channels.
  • It is used to store permanent data.

Types of Secondary Storage Devices

  • Three main types:
    • Magnetic Storage Devices
    • Optical Storage Devices
    • Solid-State Storage Devices

Magnetic Storage Devices

  • Magnetic storage stores data on a magnetized medium.
  • Three main types of Magnetic Storage Devices:
    • Hard Disk Drive (HDD)
    • Floppy Disk
    • Magnetic Tape

Hard Disk Drive (HDD)

  • HDD uses magnetic storage to store data magnetically on tracks on the disk.
  • The hard drive reads and writes data to the hard disk.
  • Platters (disks) are used to store data; data is accessed by a magnetic head.
  • A platter is a hard disk coated with a magnetic material.

HDD Advantages & Disadvantages

  • Advantages:
    • Large storage capacity up to 10 TB10\ \mathrm{TB}.
    • Stored items are not lost when the computer is switched off (non-volatile).
    • Usually fixed inside the computer and not portable.
  • Disadvantages:
    • Slower than RAM & ROM.
    • If the hard disk crashes, the computer may stop functioning and you can lose your work.

External Hard Drive

  • An External hard drive is a portable storage device that can be attached to a computer via USB cables.
  • Usually used to store media, for backups, and when the internal hard drive is full.
  • These devices have a higher storage capacity compared to flash drives.

Floppy Disk

  • Also called a Diskette; consists of a thin plastic disk coated with magnetic material.
  • Uses: To keep personal data; keep extra copies of data.
  • Advantages: Can be carried with you.
  • Disadvantages: Limited capacity (typically 1.44 MB1.44\ \mathrm{MB}); unlikely to store ICT coursework on one disk.

Magnetic Tape Storage

  • Magnetic tape is one of the oldest storage media for storing large amounts of data permanently.
  • Modern magnetic tape is commonly packaged in cassettes.
  • Advantages: It is small in size, cheap, and can store lots of data.
  • Disadvantages: Accessing data is very slow.

Optical Storage Devices

  • Optical Storage Devices are discs coated with a reflective metal on which data is recorded using laser technology.
  • Data on the storage medium is read by a laser beam off the surface of the medium.
  • Types:
    • Compact Disc (CD)
    • Digital Versatile Disc (DVD)
    • Blu-Ray Disc (BD)

Compact Disc (CD)

  • A digital optical disc data storage format; the average CD allows for up to 700 MB700\ \mathrm{MB} of data storage.
  • Digital bits are stored as pits on the reflective material in the disc.
  • A red wavelength laser detects these pits and converts them to a digital signal.
  • Three basic types:
    • Read-only: CD-ROM
    • Write-once: CD-R
    • Rewritable: CD-RW
  • Note: CD is a digital optical disc data storage format; the text repeats the same description.

CD-ROM (Read-Only Memory)

  • An optical compact disc which contains data.
  • Computers can read CD-ROMs, but cannot write to CD-ROMs (not writable or erasable).
  • Advantages:
    • Data cannot be erased
    • Portable
    • Much larger capacity than floppy disks (about 700 MB700\ \mathrm{MB})
  • Disadvantages:
    • Can’t write data to a CD-ROM

Digital Versatile Disc (DVD)

  • A DVD is an optical disc storage medium similar to a CD but with larger storage capacity.
  • DVDs allow data storage for up to 4.7 GB4.7\ \mathrm{GB} to 9.4 GB9.4\ \mathrm{GB}.
  • Uses a red wavelength laser to read data; commonly used for storing high quality audio & video.

Types of DVD

  • DVD-ROM: Read Only Memory; data can only be read, not written or erased.
  • DVD-R: Blank Recordable DVD discs can be recorded once using a DVD recorder and then function as a DVD-ROM.
  • DVD-RW: Rewritable DVDs (DVD-RW, DVD+RW) can be recorded and erased many times.

Blu-Ray Disc (BD)

  • Blu-Ray is a newer and more expansive DVD format.
  • Provides higher capacity and better quality than DVD, especially for High-Definition video.
  • A Blu-Ray disc can hold up to 25 GB to 50 GB25\ \mathrm{GB} \text{ to } 50\ \mathrm{GB} of data.
  • Blu-Ray uses a blue wavelength laser to read data.

Solid-State Storage Devices

  • Solid-State Storage is a type of non-volatile computer storage that stores data electronically instead of magnetically or optically.
  • Solid-State Devices have no moving mechanical parts.
  • SSDs operate much faster than other storage devices because there is no need to move a head or sensor to find data or convert it from magnetic or optical form into electronic form.

HDD vs SSD

  • SSD stores data electronically on microchips and contains no moving parts.
  • HDD records data magnetically on a storage platter by moving a mechanical arm with a read/write head over a spinning platter.
  • SSD is faster than HDD.

Flash Memory

  • Flash Memory is a special type of memory chip that combines the features of RAM & ROM.
  • It is used for storage and for transferring data between digital devices.
  • Flash Memory is non-volatile.
  • It is commonly used in digital cameras, multimedia players, USB & cell phones.

USB Storage Device

  • A USB flash drive — also known as a USB stick or pen drive — is a plug-and-play portable storage device that uses flash memory and is used for storing & transferring data.
  • It is lightweight enough to attach to a keychain.
  • USB Drives now come in capacities ranging between 8 GB8\ \mathrm{GB} to 2 TB2\ \mathrm{TB}.
  • Easy to transfer data from one place to another.