1.1.3 Input, output and storage

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Peripheral Devices: An Input/Output device. Any device that is used to enter information and instructions into a computer for storage or for processing and delivering processed data to the user.

Input Devices: These are used to pass data into the computer and allow the user to communicate with the computer. Examples:

  • Keyboard – a panel of keys that operate a computer.
  • Touch Screen – a display device which allows the user to interact with a computer by touching areas on the screen.
  • Pointing Devices (Mouse, stylus, touch pad) – a device used to control the movement of a cursor on a computer screen.
  • Graphics Tablet – a device that allows users to ‘draw’ in a similar way to using paper and pen.
  • Microphone – a device for converting sound waves into electrical energy variations, which may then be amplified, transmitted or recorded.
  • Scanner (2D/3D) – a device for examining, reading or monitoring something.
  • Cameras – a device for recording visual images in the form of photographs, film or video signals.
  • Sensors – a device which detects or measures a physical property and records, indicates, or otherwise responds to it.
  • Accessibility Devices – assistive technology are devices that provide support for user with additional needs. For example: foot mouse, braille keyboard.

Output Devices: These are used to report the results of processing from a computer to the user and allow the computer to communicate with the user. For example: printer, speaker & monitor. Examples:

  • Screens (Monitors) – a flat panel or area on an electronic device on which images and data are displayed.
  • Projectors – a device that is used to project rays of light, especially an apparatus with a system of lenses for projecting slides or film on to a screen.
  • Printers (2D/3D) – a machine for printing text or pictures, especially one linked to a computer.
  • Actuators – a device that causes a machine or other device to operate.
  • Motors – a machine that supplies motive power for a device with moving parts.
  • Accessibility Devices – assistive technology are devices that provide support for user with additional needs. For example: screen readers, speakers.

Secondary Storage: – The long term, non-volatile storage of data.

The need for secondary storage: 

As RAM is volatile, any data or programs currently being stored there will disappear once the power is lost. This is when secondary storage comes in. Secondary storage is used to store a copy of programs and data that need to be kept long term.

Primary Storage: – The short term, volatile storage of data.

Data Capacity: – This is how much of data a device can store.

  • The Bit: – This is the smallest unit of data that can be stored. It is often referred to as a ‘Binary digit’
  • The value of a bit can be either 0 or 1.

Ranking Order of Capacity:

  • Bit
  • Nibble (4 Bits)
  • Byte (8 Bits)
  • Kilobyte (1024 bytes)
  • Megabyte (1024 Kilobytes)
  • Gigabyte (1024 Megabytes)
  • Terabyte (1024 Gigabyte)
  • Petabyte (1024 Terabyte)

Optical Storage:

  • Optical storage uses laser light to retrieve data from the surface of optical media.
  • Optical storage is often used to deliver multimedia content such as video.

Storing a bit: Each 1 or 0 is represented as a microscopic hole, which called a pit, or a flat surface, called a land, on the surface of the disk.

Accessing data: A laser is shone on the disk surface.

  • If the laser hits a land, it will be reflected into a sensor.
  • If the laser hits a pit, then it will be reflected elsewhere.
  • This can be used to represent 1 and 0.

Properties of Optical Media:

  • Low Capacity – Disks are small and fairly cheap, so it can be easy to gain a high capacity of storage by buying multiple disks. (Low capacity per disk)
  • Slow Speed – the parts in the optical media drive have to move to find the right bit of data on the disk, this means that the access times can be quite slow and writing to a disk is a slow process.
  • Great Reliability – Optical media is waterproof and shockproof. (robust) This makes it ideal for portability (transporting) However, moving parts can cause the disk drive to break and can be scratched.

Types of Optical storage:

  • Blu-Ray Disks (BD) – These are used to store high definition movies or games. There store around 25GB of data.
  • Compact Disk (CD) – CDs are the original optical media standard. A single CD can store about 700MB of data. CDs are very cheap to produce.
  • Digital Versatile Disk (DVD) – These are often used to store games or standard-definition movies for home viewing. A single DVD can store around 4.7 GB of data.

Form of Optical storage:

  • Re-writable (RW) – A CD-RW, DVD-RW, OR BD-RW is a disk which can be overwritten whenever the user would to. These are often used for backups which might be updated in the future.
  • Write-once (R) – A CD-R, DVD-R, OR BD-R s a disk which can be written once by the user at home. This means that once the user has written data to the disk, they cannot overwrite it.
  • Read-Only Memory (ROM) – A CD-ROM, DVD-ROM, or BD-ROM is a disk which can be read only. This is because the manufacturer writes the initial data, and this cannot be changed. This is often used in content distribution so that people cannot accidentally overwrite the content.

Magnetic Storage:

Storing a bit: The value of each bit of data (0 or 1) is represented as a positively or negatively charged magnetic particle.

  • These particles are part of a magnetic disk called the platter.

Accessing Data: Data is stored magnetically in small areas called sectors within circular tracks. A magnetic read/write head is used to access sectors while the platter spins.

Reliability:

  • The Hard Disk Drive has moving parts.
  • Although the HDD is generally reliable, any device with moving parts will be subject to wear and tear.
  • Also, they can be damaged by shocks and vibrations. They are not robust.

Properties of Magnetic Media:

  • Slow Speed: Magnetic media have moving parts. This makes magnetic media slow to access.
  • Good Reliability: Magnetic media is reliable and lasts for a long time. However, it is not robust, it tends to break on impact or during vibrations.
  • Low cost: Magnetic media is very low cost per gigabyte (or low cost per unit capacity)
  • High capacity: Magnetic media can store a large quantity of data in a compact way. This makes them an ideal choice for archives and home computers.

Example of magnetic storage:

  • Hybrid drives: Combination of magnetic and solid state storage is knowing as a hybrid drive. This offers the benefits of both systems. (Been told that this will not be asked in the exam, but you never know. No harm in not knowing)
  • Hard Disk Drives: (HDD) – Main form of secondary storage in a computer system. Stores the operating system, applications and user data.

Magnetic tapes:

These are used for archiving due to the fact they have a much greater storage capacity than HDDs.

They come in plastic cassettes which contains reels of tape. A cassette requires a special tape-drive for read/writing.

Tape is read and written sequentially. This means that it reads/writes from the beginning to the end. (or stopped by the computer) This means tape is very slow when finding specific data stored on it. However, it has a fast read/write speed once it is in the correct place to begin reading/writing.

Solid state storage:

Storing a bit: Solid state drives are made of flash memory. Flash memory stores the value of each bit in a semi-conductor chip.

Reliability:

  • Solid state drives are robust. They have no moving parts. This means they are not easily damaged by shocks or vibrations.
  • SDD have a limited number of read/write cycles. They can only be flashed (rewritten) a certain number of times before they start to degrade.

Accessing Data: Data can be assessed randomly. This means that any piece of data can be accessed in a constant amount of time. This is achievable because there are no moving parts.

Properties of solid state media:

  • High speed: Solid stare media have very fast read/write times compared to magnetic and optical storage media.
  • High cost: Solid state media has a higher cost-per-GB compared to magnetic media. A person may pay more for the increase in performance. For example, faster data access speeds.
  • Good capacity: They have a good capacity but not on the scale compared to magnetic media.
  • Good reliability: Solid state drives are robust. They have no moving parts. This means they are not easily damaged by shocks or vibrations.

Virtual Storage: (The combination of physical storage devices into a virtual single storage device)

  • It is remote storage that can be accessed anywhere.
  • There is no need to hire specialist staff or back up the data as security is someone else’s responsibility.

Memory: (Where Binary Data (in 0s & 1s) is stored)

RAM: Random Access Memory.

ROM: Read Only Memory.

Purpose of RAM:

  • Stores data that is currently in use so it can be accessed quickly by the device’s processor.
  • When programs are opened by the user, they are loaded from secondary storage onto the RAM. This is so that the CPU can access the data and instructions at a quicker rate. This is because if the CPU reads the program instruction and data from secondary storage then the data access would be extremely slow. This is why RAM is so important.

Purpose of ROM:

  • Stores the boot instructions of the computer that allows the CPU to access in order to start the computer.

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