peripherals and interfaces

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Unit 1 Computer Systems

Peripherals and

Interfaces

St Kentigern’s Academy



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



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



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.



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.



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.



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.



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.



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.



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.



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



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:



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



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.



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.



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



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.




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.




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.




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.




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.




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.



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.



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.



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.



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!!!



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.



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).



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



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.



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.



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.



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



Features and Advantages of


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.





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.





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.



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.




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.




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.



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.



Selection of Suitable

Hardware

The possession of a basic computer systemconsisting of processor, monitor, keyboard,mouse and hard disk is assumed.




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




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.




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.



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




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.




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.




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.




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.




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.




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)




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.




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.




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.

peripherals and interfaces

Documents