Higher Computing: Unit 1: Topic 4 – Peripherals St Andrew’s High School, Computing Department (4-2-12)1 Higher Computing Topic 4 Peripherals

St Andrew’s High School, Computing Department (4-2-12)

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Higher Computing: Unit 1: Topic 4 – Peripherals

Higher Computing

Topic 4Peripherals


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Input Devices

KeyboardsAs well as the traditional QWERTY keyboard you should realise that there are alternative designs that are specialised to carry out less traditional tasks. An example is the Dvorak keyboard.


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Input Devices - Scanners•The flatbed scanner can normally work with documents up to A4 size. When a document is scanned the resultant digital representation of the scanned image is a bit map.•Accuracy is a measure of how close the computer image representation is to the original. This is influenced by the resolution and bit depth capability of the scanner.


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Input Devices - Scanners•Resolution is measured in dpi (dots per inch). •An image with a resolution of 600 dpi that measures 4 inches by 6 inches will have:-

inches x inches x dpi x dpi=4 x 6 x 600 x 600 bits (pixels)=8640000 bits / 8=1080000 bytes / 1024=1054.6875 Kb =1055 Kb to store the file


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Input Devices - Scanners•Bit depth describes the number of bits that is used to store the colour of a pixel. For example, 8 bits can represent 256 colours. Most scanners nowadays have a bit depth of 24 bits; this means that each pixel can have one of 224 colours.


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Input Devices - Scanners•A scanned picture measures 5 inches by 4 inches and has been scanned by a scanner with a resolution of 600 dpi and a bit depth of 24 bits. How much storage would be required for the scanned image? inches x inches x dpi x dpi x colours

=5 x 4 x 600 x 600 bits x 3 bytes=21600000 bytes / 1024=21093.75 Kb / 1024=20.599 Mb =21 Mb to store the file

(24 bits = 3 bytes)


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Input Devices – Digital Cameras•A digital camera is one of the fastest ways to use pictures into a computer. No need to develop film or scan images from a printed copy. Pictures are ready to use right away in presentations or send in email messages. It is possible to print at home and achieve photo quality results.•Digital photos are bit maps, made up of thousands or millions of pixels with values to represent image brightness and colour. Digital image data is stored in a memory card inside the camera.


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Input Devices – Digital Cameras•Accuracy is measured by the resolution and bit depth capability of digital camera.•In cheaper range cameras the resolution is of VGA standard i.e. 640 x 480 pixels, capturing 307,200 pixels in each picture. •Other cameras support "megapixel" representation, able to take high-resolution shots at 1024 x 768 or 1280 x 960 pixel resolution.•Most cameras have a bit depth of 24 bits


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Input Devices – Sound Cards•Sound is an analogue signal and needs to be converted to a digital form to be able to be stored/used by a computer. •Digital representation is achieved by sampling the sound. The more often a sample is taken, the sampling frequency, and the more data that is stored about each sample, the sample size, the better the quality of sound that is represented.


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Input Devices – Sound Cards•How closely the digitised sound matches the original will clearly depend on the sampling frequency and sample size. •The higher the sample frequency and the more bits used per sample, the closer the digital representation will be to the original analogue form.•Sound is stored directly to disk and so it does not really make sense to talk of the capacity of a sound card. As with all digitisers, you should be aware of the amount of backing storage that will be required to hold the data permanently.


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Input Devices – Sound Cards•A simple calculation with a sample frequency of 44.1 kHz (CD quality), a sample size of 16 bits, lasting for 2 minutes requires: Number of Samples =44100 x 120 (secs)

=5292000

Number of Bytes Required

=5292000 x 2 bytes=10584000 bytes / 1024=10335 Kb / 1024=10.09 Mb


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Output Devices – Inkjet Printers•Resolution is typically 300 to 600 dots per inch. They support the printing of text and graphics, colour and a range of shades. Speed is pretty slow with a range of 4 pages per minute to 8 pages per minute, depending upon the model.


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Output Devices – Laser Printers•Resolution is typically 300 to 600 dpi, although higher resolutions are available if you are prepared to pay the price. Colour and a range of shades are supported. Speed ranges between 4 pages per minute and 40 pages per minute.


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Output Devices – Monitors•Scan Rate – number of times the screen is re-drawn. That is the number of times it scans from the top of the screen to the bottom per second. This rate needs to occur at least 50 times per second, (50 Hz) to stop screen flickering.•A video graphics adapter sets the scan rate and some manufacturers provide adapters with different screen proportions and resolutions. A resolution of 640 x 480 pixels (VGA) will require a different scanning rate than a resolution of 800 x 600 pixels (SVGA). •Multiscan monitors are able to deal with these different scanning frequencies.•TFTs are flat panels common in desktops/laptops.


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Buffers

•A buffer is an area of RAM (computer memory), normally on the device eg printer. It is allocated to transferring data between the computer and a peripheral. A buffer will be used when a fast acting part of the system is exchanging data with a slow acting device. The buffer stores data until it can be dealt with. For example, a printer operates at a much slower speed than the computer. A program can continue operating without waiting for each character to be printed if the data is sent to a buffer. The buffer is normally managed by the operating system, which sends the data to the printer when it is ready to receive data.

Buffers store data after the data has been received (data received by a printer and stored and waits till it is printed out).


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Spoolers•When large amounts of data are to be sent to a peripheral device, or when the peripheral is shared across a network then spooling is a preferred method of coping with the difference in speeds of the processor and the peripheral. •Spooling involves the input or output of data to fast backing storage (eg disk). This, for example, allows output to be queued from many different programs and sent to a printer by a print spooler (special operating system software). The print spooler stores the data on fast backing storage in files and sends it to the printer when it is ready, using a print queue.

Spoolers store data before it is sent (eg queue for the printer, data is still to be sent to the printer).


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Backing Storage Devices – Hard Drive (Magnetic)•All the sectors around the disk, equidistant from the centre, form a track. With multiple platters, the collection of tracks on each platter, equidistant from the spindle is called a cylinder. When data is to be read or written, the read and write heads are moved to the appropriate track, where they wait until the relevant sector spins past.•Speed•The speed of access to data stored on a hard disk depends on the rotational speed and the type of interface being used, for example, SCSI.


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Backing Storage Devices – Hard Drive (Magnetic)•Capacity•Hard disks have improved tremendously in their capacity to store data in the last 10 years. Many of today’s PCs have 80Gb hard disk drives.•Access•The hard disk is a direct access device, meaning that data can be directly read or written to any portion of the disk.


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Backing Storage Devices – Tape Storage (Magnetic)•Storing data on tapes used to be the only solution to backing up hard disks of large capacity. Tape is read and written on a tape drive. This drive winds the tape from one reel to the other causing it to move past a read/write head.•Capacity•Magnetic tapes have large capacities, typically up to 20 Gb.


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Backing Storage Devices – Tape Storage (Magnetic)•Access•Tapes are sequential access devices, which means that to get to a particular block of data on the tape, it must go through all the preceding blocks of data. Accessing data on tapes is therefore much slower than accessing data on disks.•Not suitable when data needs to be used regularly - disk is more appropriate. Because tapes are so slow, they are generally used only for long-term storage and backup.


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Backing Storage Devices – CD-ROM, R, R/W (Optical)•The most common optical storage device is the CD-ROM. Read-only medium whose contents cannot be altered once data is written to it.•The read-only limitation of CD-ROMs has been overcome by the creation of writeable CDs. CD-Rs can be written to once with a CD-Writer, and CD-RWs can be written to many times using a CD re-writer.•Capacity•CD-ROMs are typically 650/700 Mbytes in capacity.


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Backing Storage Devices – CD-ROM, R, R/W (Optical)•Speed•In a single speed CD reader, audio data can be read adequately, but is very slow for motion video or large image files. Multiple speed CD readers, such as 48xCD-ROM or 24xCD-ROM can read these types of files properly. •Write and Rewrite speeds are also multiples of the single-speed rates. For example, a re-writable drive advertised at x48 x16 x4, means that it can read CD-ROMs at x48, write once to CD-R at x16 and re-write to CD-RW at x4.•Access is Direct


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Solid State Storage Devices Solid-state storage devices are made up entirely from electronic components i.e. they have no moving parts. They are also called RAM disks, as they take the place of a magnetic disk as a mass storage device. They can be in the form of a plug-in card or cartridge containing memory chips. The chips of a SSSD are typically static RAM or Electrically Erasable Programmable ROM (EEPROM or Flash EPROM).•SSSD are used with devices where space is at a premium e.g. in a camera, or when portability is desirable e.g. a USB flash drive.


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Interfacing Interfacing hardware means making the appropriate connections so that two pieces of equipment can communicate or work together effectively. This section considers the 4 factors that have to be resolved between the devices before communication can happen.


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Interfacing - Data Format Conversion• Data to be communicated has to be

arranged in such a way to be understood by the hardware or software doing the sending or receiving. The data format may have to be converted from

– serial to parallel and vice versa eg keyboard input (serial) needs converted to parallel

– or from analogue to digital and vice versa eg an analogue input sensor on a robot must converted to digital using (ADC). For an analogue output device eg motor the signal must be changed from Digital to Analogue (DAC).


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Interfacing - Voltage Conversion• Voltage is the electrical force that

allows devices to work. It is also required to send data signals between devices. As devices operate and send signals at differing voltages then these quantities must be changed to allow successful communication.


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Interfacing - Protocols Conversion• A protocol is a set of rules that

govern the transmission of data. Certain standards are set to allow for successful communication.

• The standard (or protocol) will dictate things like data format, timing, voltage levels etc required by devices to allow for data exchange.


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Interfacing - Status Signal HandlingStatus signals are messages passed between the processor and peripherals. Status signals can confirm that data has been sent/received. Status signals confirm whether a device is ready to send/receive data. Eg the status of a hard disc must be established before the processor sends data to be written to the disk, the disk may be reading data already, the processor must delay transmitting the data until the status of the hard disc changes to idle.


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Not in ArrangementsInterfacing - Buffering• Different devices send and receive

data at different rates. If a device sends data at too high a rate, then the receiving device must cope with that, possibly by buffering the data, ie, storing it until it is able to deal with it.


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Interfacing - Types of Interfaces• The type of interfaces that are in

use today include:

Fast

Interface Typical Use

Serial Mouse/Keyboard

Parallel Old printers

USB Current printers, digital cameras, etc

Firewire Digital video

Slow


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Interfacing - Wireless Communication• At the moment the move is towards

wireless technology – wireless keyboards, mouse, etc. Wireless communications can be achieved using WAP (Wireless Application Protocol). This, like any protocol, is a set of communication rules to standardise the way that wireless devices can be used.

• Typically, wireless communication allows communication between devices in a short radius of about 10 metres. One such technology is Bluetooth.

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Higher Computing: Unit 1: Topic 4 – Peripherals St Andrew’s High School, Computing Department (4-2-12)1 Higher Computing Topic 4 Peripherals