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 $10\ \mathrm{TB}$.
  • 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 $1.44\ \mathrm{MB}$); 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 $700\ \mathrm{MB}$ 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 $700\ \mathrm{MB}$)
• 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 $4.7\ \mathrm{GB}$ to $9.4\ \mathrm{GB}$.
• 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 $25\ \mathrm{GB} \text{ to } 50\ \mathrm{GB}$ 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 $8\ \mathrm{GB}$ to $2\ \mathrm{TB}$.
• Easy to transfer data from one place to another.