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8/10/2019 Peripherals and Interfaces
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Unit 1 Computer Systems
Peripherals and
Interfaces
St Kentigern’s Academy
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What I need to know…
Description of the use and advantages of buffers andspooling;
Description of a suitable selection of hardware, including
peripherals, to support typical tasks including productionof a multimedia catalogue, setting up a LAN in a school,development of a school website;
Justification of the hardware selected in terms of
appropriate characteristics including resolution, capacity,speed, cost and compatibility;
Description of the features, uses and advantages of solidstate storage devices including flash cards
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What I need to know…
Description of the development trends in backingstorage devices;
Description of the following functions of an interface:
buffering, data format conversion (serial to paralleland analogue to digital), voltage conversion, protocolconversion, handling of status signals;
Distinction between parallel and serial interfaces; &
Description and explanation of the current trendstowards increasing interface speeds and wirelesscommunication between peripherals and CPU
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Peripherals
Peripherals are any device that can beattached to a CPU, e.g. hard disk, mouse,printer.
Peripherals are slow. They hold up the CPUfrom carrying out its’ tasks.
For Example - playing a game and it needs toload the next level. The level is being readfrom the CD and written to memory.
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Interfaces
What is an interface?The interface is the combination of
hardware and software needed to link theCPU to the peripherals and to enable them
to communicate with the CPU despite alltheir differing characteristics.
The hardware is the bit you connect the cable
into e.g. USB, parallel Firewire.
The software is the driver disk that you usuallyneed to install when you get the device, e.g.
printer diriver.
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Interfaces
Computer peripherals all have differentcharacteristics. For example, they may:
Have different data transfer rates;
Use a wide variety of codes and control signals;
Transmit data in serial or in parallel form;
Even work at higher voltages than the CPU; &
All operate at much slower speeds than the CPU.
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Interfaces
The main functions of an interface that you need to knowabout are:
Buffering;
Converting data to and from serial and parallel forms;
Converting data to and from analogue and digital forms;
Voltage conversion;
Protocol conversion; &
Handling of status signals.
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Interfaces
Buffering:This is an area of RAM within the interface which
stores the data while in transit between theprocessor and the peripheral.
The interface uses the buffer to temporarilystore the data it is working with.
It also uses the buffer to compensate for the
differences in speed between the peripherals andthe CPU by temporarily storing incoming data sothat the faster CPU can process it in manageableblocks rather than waiting for the slowerperipheral.
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Interfaces
Converting data to and from serial and parallelforms:Data transmission is the passing of data from one
device to another.
A serial interface uses serial data transmission;A parallel interface uses parallel datatransmission.
Serial data transmission - is when data istransmitted along a communication channel one bitafter another in sequence. Very slow but efficient
over long distances.
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Interfaces
Parallel data transmission - transmitseveral bits of data simultaneously across aseries of parallel channels, often transmitting16 at 32 bits at a time. Very fast but only
suitable for short distances.
The buses internal to the processor areparallel channels. Any data coming from aserial device has to be sent to an interfacewhich buffers the data then converts it toparallel form before it is passed to the
processor.
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Interfaces
1 0 1 0 10
1
0
1
0
1
0
1
0
1
0
1
0
Serial data format
Interface
Parallel data format
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Interfaces
Converting data to and from analogue and digitalforms:Analogue signals – many electrical signals are analogue
signals. These signals vary between two limits. Analoguesignals that are sent in from peripherals to the digital form
that the CPU can handle. If you could see an analogue signalit would look roughly like this:
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Interfaces
Digital signals – computers can only work with digitalsignals, which have only two values – on or off. A digitalsifnal therefore consists of a series of ‘ons’ and ‘offs’. Anon signal is represented by a 1 and an off by a 0
0 1 1 0 0 1 1
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Interfaces
ADC and DAC A computer is connected to a peripheral
by an interface. This interface has to be
able to change the digital signals from thecomputer to an analogue signal that theother device can understand. This is doneby a DAC – Digital to Analogue Converter.
Signals can be changed in the otherdirection by an ADC – Analogue to DigitalConverter.
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Interfaces
Voltage Conversion
Peripherals send data using a different voltagefrom that used by the processor and its
associated components on the motherboard of thecomputer.
An interface is used to compensate for thesedifferences.
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Protocol ConversionA protocol is a standard that enables the connection,
communication and data transfer between computers orbetween a computer system and a peripheral. Protocol
conversion means ensuring that the protocols used by theperipheral can be understood by the computer it isattached to and vice versa.
Handling of Status SignalThe purpose of the status information is to show whether
or not a peripheral device is ready to communicate. Thisinformation is used to inform the user of a problemrequiring attention. Some printers
Interfaces
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Buffers and Spoolers
Buffers and spoolers are terms generallyassociated with printers.
The terms are not dedicated to printers butthat is the context that will be described.
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Buffers and Spoolers
What is a Buffer?
A buffer is an area of memory used for the transferof data between a computer and a peripheral.
A buffer provides temporary storage of data.
Using a buffer provides a link between a device and
the processor and helps compensate for anydifferences in their working speeds.
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Buffers and Spoolers
Why use buffers?
Peripherals operate at much slower speeds than theCPU. Using buffers helps the computer system
compensate for the differences in operating speedsbetween CPU and its peripherals.
When transferring data out to a peripheral such as aprinter, the processor can transfer it faster into thebuffer and the buffer will send it to the printer at aspeed that the printer can cope with.
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Buffers and Spoolers
Why use buffers?
The use of buffers reduces the frequency withwhich the CPU is interrupted to deal with input.Data from a keyboard is stored in a buffer untilthere is a larger amount of data for the CPU toprocess.
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Buffers and Spoolers
Spoolers
Spooling is another technique used in the transfer of
data to a slow peripherals. In this case the dataintended for the peripheral, the best example is aprinter, is transferred to storage, often a hard disk.Then when the processor is idle it will transfer thedata to the printer at an acceptable speed. This is
also called background printing.
This frees up the much faster CPU to process othertasks. Spooling is another possible method ofimproving system performance.
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Buffers and Spoolers
Buffer v’s Spooler
If the CPU is very busy and doesn’t get much idle
time then spooling can be a very slow process.
Spooler v’s Buffer
A buffer is limited by the amount of RAMwhereas a spooler uses backing storage whichhas a very large capacity.
Use BOTH for optimum efficiency.
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Current Interface Trends
and Wireless Comms.
New interfaces are continually beingdeveloped.
One focus of development is to increase thespeed at which interfaces allows theperipheral and computer to communicate.
Another aim is to allow wirelesscommunication between peripheral devicesand the CPU.
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Increasing Interface Speeds
Interface speeds are measured in Megabitsper second (Mbps).
N.B. do not confuse Megabits and Megabytes
Manufacturers normally use Megabits persecond in their advertising as this allowsthem to print larger numbers on theiradvertisements.
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Increasing Interface Speeds
One example of increasing interfacespeeds is the development of the USB 2 and the Firewire 800 interfaces.
The USB 2 improves upon the maximum 12Mbps speed of the USB 1 interface by 40times to 480 Mbps.
The Firewire 800 interface provides 800Mbps, double the speed of the Firewire 400 interface.
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Interface Standards
Interface Description
RS232 Recommended Standard (Serial)SCSI Small computer Systems Interface ( Parallel)IDE Integrated Drive ElectronicsSATA Serial Advanced Technology Attachment – up to 1.5Gbps
IEEE Institute of Electrical and Electronic Engineers e.g. firewireMIDI Musical Instrument Digital InterfacePCI Peripheral Component InterconnectPCMCIA Personal Computer Memory Card International AssociationUSB1 & 2 Universal Serial Bus
The use of interface standards by a computer manufacturer means that theircomputers will be able to connect to peripherals using the same standards.
The use of interface standards by peripheral manufacturers means that theirperipherals will connect to a computer which uses the same standards.
Makes them COMPATABLE!!!
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The latest Interfaces
Interface Description Transfer Speeds
USB1 Universal Serial Bus Fast transfer rate:A means of connecting 12 MBPS for fastexternal devices devices
USB2 An improvement of the Up to 480 MbpsUSB.
Firewire A high speed serial interface In its latest version,used for connecting audio/ IEEE 1394b, up to avisual and multimedia max of 800Mbps.applications like digital 3.2Gbps are undercamcorders. Development.
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Wireless Co
mmunication
Current trends in wireless communication includethe standards WiFi and Bluetooth.
Bluetooth and WiFi both use radio waves at thesame frequency.
Radio waves can pass through most materialsand walls, and devices do not need to be pointingat one another, unlike, infrared datatransmission (TV remote control).
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Wireless Co
mmunication
BluetoothBluetooth can make short-range links between personal
devices, such as mobile phones and headsets, palmtops
(PDA) and laptop (notebook) computers.
Bluetooth is also used for wireless keyboards and mice.
It is expected that later versions of Bluetooth will beable to transmit data at a speed of 2 Mbps and forlonger distances
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Wireless Co
mmunication
WiFiWiFi stands for the Wireless Fidelity Alliance.
The main use for WiFi is in wireless local areanetworking (WLAN). WiFi devices have typical rangesfrom 15 to 50 meters and typical data transfer ratesfrom 5 to 20 Mbps.
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Solid State Storage Devices
A solid-state storage device contains no movingparts.
Examples include flash cards and USB flash memory
Both of these types of device contain the same type ofbacking storage medium, namely flash ROM.
The effective difference between them is that they usedifferent interfaces to connect to a computer system oranother peripheral.
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Flash Cards
Flash cards are used mainly for data storage in cameras,although they can hold any type of program or data file.
There a number of different standards of flash cards.
Each digital camera normally uses only one type of flashcard
Specialised card readers have been developed which have‘slots’ to fit all the different varieties of flash cards. So called ‘all-in-one’ devices (printer, scanner, photocopies) have
slots into which flash cards may be placed. This allows documentsto be printed directly from the card, without a computer systemhaving to be connected.
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USB l sh Memory
There are two types of USB Flash Memory,according to the type of interface being used.The are USB 1 and USB 2.
Most of these devices are now compatible withUSB 2.
USB2 devices are always backwards compatible.In this case the speed of access will be USB 1
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Features and Advantages of
Solid State Storage Devices
Solid-state storage devices are small .
Flash cards can fit inside the camera.
USB flash memory can fit on key rings and inwatches.
Solid-state storage devices are robust becausethey have no moving parts.This means that they are ideal for wearing because they
are unaffected by vigorous movement.
iPods take advantage of this feature of Solid-statestorage devices.
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Features and Advantages of
Solid State Storage Devices
Solid-State storage devices use less
power than hard disk drives.This lower power requirement means that a
music player which uses solid-state storagewill play music for a longer time relative to a
hard disk-based music player with the samebattery capacity.
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Features and Advantages of
Solid State Storage Devices
Solid-state storage devices are available in a range ofcapacities, from 256 Mb to 8 Gb (at the time of writing).
USB flash memory has now replace floppy disk as aconvenient, portable storage medium, which can fit intoalmost any modern computer system.
USB flash memory is used for security applications.One type has fingerprint recognition and another type
works with security software to prevent a computer systemfrom starting up unless the USB flash memory is plugged in.
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Developments in Backing
Storage Devices
Increased capacityDVDThe DVD-Recordable format capacity was
increased with the introduction of the duallayer DVD-R disk with a capacity of 8.4 Gb
(Single –layer DVD-R capacity is 4.7 Gb)
Most computers now incorporate this duallayer drive.
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Developments in Backing
Storage Devices
Blu-rayBlu-ray disc (BD) is the name of the next
generation optical disc format.
The format was developed to enablerecording, rewriting and playback of high-
definition video (HD).
The format may become a standard for PCdata storage and high-definition movies.
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Developments in Backing
Storage Devices
Increased read and write speeds Faster interfaces are constantly being developed, e.g. USB 2, Firewire
800, with speeds of 480 Mbps and 800 Mbps, respectively
Reduced Physical Size In 2004, Guinness World Records certified that Toshiba’s 0.85 inch
diameter hard disk drive as the smallest hard disk drive in the world.
Lower Cost Per Unit of Storage In 1995, a 100 Mb capacity hard disk drive cost £300. In 2005, a 100
Mb capacity ZIP drive cost £5, and a 512 Mb USB flash memory cost£25.
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Developments in Backing Storage
Devices
Implications of Development Trends
One implication may be that new peripherals and media may notwork with old ‘legacy’ hardware. An older computer may not have a USB port, or if it does, it may
not be USB 2, only USB 1.A DVD re-writer may not be able to read or write to new disk
formats. Care must also be taken with archived data, to make sure that it
is regularly copied to a current storage format so that it canalways be accessed.
In 2004 we say some electrical stores discontinue the sales ofVHS video recorders in favour of DVD.
Digital video cameras, which record directly to DVD instead oftape are now common.
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Selection of Suitable
Hardware
The possession of a basic computer systemconsisting of processor, monitor, keyboard,mouse and hard disk is assumed.
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Selection of Suitable
Hardware
Production of a multimedia catalogue A multimedia catalogue is a database of products or items
which contains variety of media, such as sound, graphics andvideo.
The following list of hardware and media would be
appropriate to support this task: Digital video camera Digital still camera Graphics tabletMicrophone – may be part of the computer system Sound card - may be part of the computer system
Video capture card - may be part of the computer system ormay require to be purchased separately
Additional backing storage:• External hard disk• CD-R/DVD-R drive – most computer systems have these as standard• Blank CD-R and DVD-R media
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Selection of Suitable
Hardware
JustificationResolution – an expensive professional standard of
video camera is not essential.
A still camera of 2-3 megapixels resolution would beappropriate since enlargements of images are notrequired, they are only to be displayed on a screen.
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Selection of Suitable
Hardware
CapacityDigital video camera - minimum 5 minute recording
time.
Digital still camera – a 256 Mb flash memory cardwould hold over a hundred images at 3 megapixels(compressed as JPEG). Additional hard disk, around200 Gigabytes.
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Selection of Suitable Hardware
CostDigital still camera £100,
Digital video camera £300,
additional hard disk £200,Video capture card £100,
Sound card £100,
Graphics tablet £100,Blank media:CD-Recordable £15 per 100,
DVD-Recordable £15 for 25
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Selection of Suitable Hardware
CompatibilityJPEG is a standard format for still images.
Mini DV format is supported by a wide range
of digital video cameras.IEEE 1394 (Firewire) is a standard interface
for digital video cameras.
USB is a standard interface for digital stillcameras.
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Selection of Suitable Hardware
Setting Up a LAN in a School Local Area Networks are common in schools.
In order to be connected to the network,each computer system must have a network
interface card.
Suitable cabling such as category 5unshielded twisted pair (UTP) must be
installed throughout the school in order toconnect the computers together and createthe network.
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Selection of Suitable Hardware
Depending on the topology chosen,switches of hubs may be required.
In addition a suitable number ofprinters may be added.
A fileserver is required to create aclient-server network.
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Selection of Suitable Hardware
As an alternative to cabling the school,a wireless network may be set up.
At least one wireless base station willbe required, depending upon the physical
extent of the network.
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Selection of Suitable
Hardware
Each computer will require a wireless networkcard in order to communicate with the base
station.
Other servers, such as database or web, maybe required depending upon the application(s)of the LAN. A network operating system isalso required, although this section only dealswith hardware.
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Selection of Suitable Hardware
Justification
Speed – A minimum of 100 Mbps for the transmission
speed of the network including hubs,switches, cabling and network interfacecards.
A server, if required, should use a gigabitnetwork interface (1000 Mbps)
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Selection of Suitable Hardware
Development of School WebsiteVery little additional hardware other than
the basic computer system described above
is required to create a school website.
A digital still camera would be useful for
photographs of school activities and events.
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Selection of Suitable Hardware
Justification
ResolutionA digital still camera of 2-3 megapixels
resolution would be appropriate sinceenlargements of images are not required,
they are only to be displayed on a screen.
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Selection of Suitable Hardware
Capacity Digital still camera
a 256 Mb flash memory card would hold over a hundredimages at 3 megapixels (compressed as JPEG).
Additional hard disk, around 200 Gigabytes.
CostDigital still camera £100
CompatibilityThe developed website should be tested on a range of
browsers running under a variety of operating systems toensure the widest possible compatibility.