Topic 7.4 - External Hardware Devices

• Barcode Definition


  - Printed diagrams that consist of light and dark portions. They contain information that can be read by a computer using a barcode reader.

  - Two types: 1D and 2D (QR code).

  - 2D barcodes contain more information in the same amount of space, but require more processing for the information to be extracted.
• Barcode Reader Function


  - Mirror directs light from the laser onto a printed barcode.

  - Any light reflected from this passes through a lens and onto a photodiode, turning light into electrical charge.

  - This charge is measured and processed to form a digital signal representing the content of the barcode.

  - Light portions reflect the most light while dark sections involve incident light. These correlate to binary 1s and 0s.
• Barcode Error Detection


  - Can have check digits or parity bits built in, allowing a computer to know if the barcode has been read correctly.

  - If a barcode fails to scan E.G. due to obstruction, the reader will continue to scan until it has been read successfully.
• Digital Camera Components


  - Consists of a lens that focuses light onto a sensor.

  - The path of light between the lens and sensor is regulated by a shutter.
• Digital Cameras Function


  - Light enters through the lens; onto the sensor chip (CCD or CMOS);

  - Each sensor produces an electrical current/signal representing a pixel;

  - An (ADC) converts measurement of light intensity into digital data;

  - Filter is applied to generate separate data values for red, green and blue colour components;

  - The pixels are recorded as a group / array;
• Laser Printer Components


  - Output device that produces images on paper from digital signals, printing a whole page at a time.

  - Consists of a laser light source, a mirror, a drum, a toner roller, and fusers.
• Laser Printer Function (1)

  - Print drum coated in (positive static) charge.

  - Printer generates bitmap of page from the data.

  - Laser beams directed at print drum via rotating mirror.

  - Laser reverses electric charge on drum where image should be dark.
• Laser Printer Function (2)

  - Toner is given (positive) charge.

  - Charged drum picks up toner.

  - Toner transferred (from drum) to paper.

  - Toner is fused to paper by heated rollers.
• RFID Components and Definition

  - A method of transferring information wirelessly between a tag and a reader.

  - Inside an RFID tag is a chip containing a small amount of memory. The chip is attached to a coil of wire that acts as an antenna.
• Passive and Active RFID

  - Passive RFID tags induce enough power wirelessly from the reader to operate the chip. Most RFID tags are passive.

  - Active tags that contain a power supply E.G. a battery also exist, and can be held much further away than passive tags.
• RFID Function


  - When an RFID tag is scanned, the reader emits radio waves that are picked up by the tag's antenna.

  - The power induced in the tag's antenna is enough to power the chip which uses its antenna to emit its own radio wave, containing the information of the chip.

  - Wave is picked up by the reader which decodes the information and returns it to a computer.
• Primary vs. Secondary Storage

  - Primary storage is RAM or ROM (limited).

  - Secondary storage includes hard disk drives (HDDs), soild state drives (SSD), and optical disks.
• Hard Disk Drives Components

  - Consists of several magnetic circular platters.

  - Above each platter hovers an actuating arm containing a read/write head.
• Hard Disk Drives Function

  - The read/write head changes magnetic polarity of parts of the platter and the arm allows it to read the whole platter.

  - Data is written in concentric tracks, each of which is further divided into sectors.

  - The platter rotates thousands of times per minute.
• Hard Disk Drives Evaluation

  - Good read/write speeds.

  - High capacity (usually 500GB - 5TB).

  - Bulky and very susceptible to damage from movement, making them unsuitable for use in portable devices like phones.
• Solid State Drive Componenets

  - Consists of NAND flash memory cells and a controller that manages the structure of the data on the drive.
• Solid State Drive Function

  - NAND memory is non-volatile, so SSD contents are retained when there is no power supply.

  - Based on floating gate transistors that trap and store charge.

  - Data is stored in pages, which combine to form blocks.
• Solid State Drive Evaluation

  - SSDs are not capable of overwriting data, the controller must entirely erase a page before writing new information to it.

  - Due to no moving parts, read/write speeds are very quick, and suitable to be used in phones.

  - Relatively low capacity, usually under 1TB.
• Optical Disks Components


  - Include CDs, DVDs, and Blu-rays.

  - Can be read-only, recordable, or rewritable.
• Optical Disks Function


  - Low-powered lasers are reflected off of the disk onto a photodiode.

  - Pits scatter the light, lands reflect it directly. This correlates to binary 0s and 1s.

  - Recordable and rewritable disks use dye instead of permanently burnt-in pits.
• Optical Disks Evaluation


  - Very low capacity, highest are 25GB.

  - Lowest read/write speeds.

  - Small and lightweight, but damaged by scrapes and dirt.

  - Suitable for sharing and distributing small volumes of data.