input, output and storage

1.1.3 a) uses of input, output and storage devices

• input devices include:

  • keyboards, webcams, magnetic stripe readers or barcode readers

• output devices include:

  • speakers, printers or projectors

• a touch screen is both an input and an output device

• performance factors for both input and output devices include..

  • speed, accuracy, cost and relevance to task

1.1.3 b) magnetic, flash and optical storage devices

optical storage

• read from and written to using lasers

• binary information represented by portions of the disc which either reflect or scatter the incident laser light:

  • a pit scatters light and represents a 0

  • a land reflects light and represents a 1

• pits and lands are written in spiral tracks on the disc’s surface

Compact Discs (CDs):

• use optical technology to store small quantities of information

• most commonly used for audio files

• can also be used to store text and digital images

• small, thin and light so very portable

• easily damaged by scratches

• limited storage capacity

• relatively slow transfer speeds

Digital Versatile/Video Discs (DVDs):

• higher storage capacity than CDs

• suited to storing digital videos

Blu-Ray:

• more than five times as much storage than traditional DVDs

• useful for storing ^^high-resolution films ^^

magnetic storage

• represent binary information using two magnetic states

  • polarised

  • un-polarised

• most common type is hard disk drives

• magnetic tape also stores information magnetically

Hard Disk Drives (HDDs):

• typically have high capacities of between 500GB and 5TB

• rotate magnetic platters at high speeds under a read/write head on an actuating arm

• most will have multiple platters stacked to maximise storage capacity

• have somewhat slow data transfer speeds

• many moving parts introduces tendency to be damaged by movement

magnetic tape:

• popular storage medium through to the 1980s

• long stretches of tape wound onto reels passed through readers

• a space consuming way to store data

floppy disks:

• a thin magnetic disk enclosed in plastic to protect the disk from dust and dirt

• thin size and low weight made them extremely portable

• typical storage capacity of 1MB

flash storage

• logic gates used to store electrical charge in one of two states: high or low

• silicon semiconductors form the logic gates NAND and NOR

  • NOR gate is used for storing small quantities of data

  • NAND is the preferred technology for larger files

• information stored in blocks, combined to form pages

• can be erased and reprogrammed electronically

• fast and compact form of storage

• flash memory is generally more expensive per gigabyte than other methods of data storage

Solid State Drives (SSDs):

• extremely light and portable

• no moving parts

• much more resistant to damage from movement than hard disk drives

• renowned for high data transfer rates

• primary disadvantage is cost

• another disadvantage is limited lifespan:

  • when a page is written to, the voltage required increases..

  • over time, this will become too high

1.1.3 c) RAM and ROM

Random Access Memory (RAM):

• fast, volatile main memory

• stores data and programs that the computer is currently using

• speeds up the computer’s execution

• higher access speeds than even flash memory

• more expensive per gigabyte than secondary storage devices

• computers often have only 4 - 8 GB of RAM

Read-Only Memory (ROM):

• non-volatile

• cannot be modified

• once programmed, the state of the memory cells inside does not change

• useful for storing fixed sequences of instructions like a computer’s startup (bootstrap) routine

1.1.3 d) virtual storage

• name given to storing information remotely so that it can be accessed by any computer with access to the same system, for example over the Internet (e.g. cloud storage services and networked storage used in offices and schools)

• as internet speeds increase, virtual storage is becoming more popular

• often an abstraction of multiple drives acting like one

• disadvantages include:

  • limitations of a user’s network speed

  • high costs