Transcript Higher Grade Computing

COMPUTING
(Higher)
Unit 1
Computer Systems
Topic 3 – Peripherals
Slide 1
PERIPHERALS
Systems Booklet 2- Pages 3 - 4
What is a Peripheral?
Any hardware device external to the processor or main
memory is called a PERIPHERAL. These are used for
• Input, (Keyboard, Bar Code Reader, Microphone,
Webcam etc.)
• Output (Printers, VDU’s, LCD Panels, etc.) and
• Backing storage (Magnetic Tape, Optical Disk,
Solid State Storage, etc.)
Their ‘job’ is to connect the processor to the outside
world. However, most peripheral devices are designed to
be general-purpose, in that their design takes no account
of which processor they may be connected to.
Slide 2
Peripherals also work at much slower speeds than
the CPU. This is helped by
• Buffers and spooling. (look at later)
• Sound cards can have their own processor
and RAM.
• Video cards have their own own processor
and RAM.
As peripherals are processor independent, the
signals from them are not always compatible with
these peripherals, and in these cases an
INTERFACE is required.
What is an Interface?
An interface is the unit, hardware or software,
which allows two pieces of equipment that would
otherwise be incompatible to communicate with
each other. Interfaces allow for differences in speed
and data between peripherals and the processor. Slide 3
What does it do?
The interface is responsible for
• Data Conversion - changing data from the processor
form to the peripheral form (and vice versa)
• Data Storage - providing temporary storage of data
in transit.
• Status Information - supplying information to the
CPU concerning the readiness of peripherals.
• Control Signals - receiving and generating signals
for the control of the peripheral.
• Device Selection - find out which peripheral is
talking to the processor, or select as necessary
Slide 4
• Voltage – different voltage levels between
peripheral & computer need to be ironed out.
• Protocols – rules that govern transmission of data.
E.g. no of bits per packet, voltage levels etc.
• Speed - Different devices send and receive data at
different rates. The devices agree a rate prior to
transmission by utilising a protocol.
Slide 5
In some cases parallel to serial conversion is
required
• Some devices are serial,
• e.g.1 bit at a time is transferred.
• Serial used for long (over 2m) distances.
• Some are parallel (printers),
• e.g.8 bits at a time.
• Used for short distances
• Problems with skewing – loss of data
integrity.
Serial can be slow but current use of fibre-optic
cable makes it very fast.
Slide 6
Buffers
Since modern processors work at very high speeds, one
of the main problems associated with peripherals is, as
said previously, speed incompatibility between
themselves and processors.
To speed up processing, most computers have
specialised high-speed areas called buffers.
• An input buffer is a waiting area holding blocks of
data transferred from a peripheral.
• An output buffer stores data already processed by
the CPU awaiting output (for example to a printer).
Slide 7
Simultaneous Peripheral Operation
On-Line (Spooling)
This is another method of providing efficient use of
the processor. Data is sent to a spool file on backing
store until the output device is ready for it. (e.g.
Background printing)
Slide 8
Memory Mapped I/O
The physical layout of a particular memory system is
called a Memory Map and it shows the organisation
of memory.
Most processors use part of
their main memory to access
interfaces and if the processor
wants to send data to a
peripheral it writes the data to
the location specific to that
peripheral, i.e. its address.
Data can also be read from that
same location.
This is memory mapped I/O
Slide 9
Input & Output Peripherals
Keyboards
QWERTY keyboard
• has its roots in mechanical typewriters. The key layout is
designed to slow down operators to avoid jamming the
keys.
• Key press causes a code to be sent to the computer.
• Sent via serial coble to keyboard controller.
• Sent as ASCII Codes
Modified Keyboards
• Used to alleviate Repetitive Strain Injury (RSI)
• Customised keypads can have more (or fewer) keys all
programmable to suit particular situations.
• Adjustable split keyboard in 3 parts to allow flexibility.
Slide 10
Input & Output Peripherals
Scanners
Scanners
• Flat bed scanner allows for up to A4 size documents
• Document placed face downwards on glass panel and
scanned.
• Light beam reflects light from the document and photocells
measure the light reflected.
• Analogue data needs converted to digital (A DC)
• Modern scanners use high bit depths to allow high resolutions.
• Images must be matched to their purpose
• No point in scanning at a resolution of more than 75 dpi for a
screen based display.
• No point in scanning at 600 dpi for a printer rated at 300 dpi.
Slide 11
Input & Output Peripherals
Scanners
Accuracy – measured by how close the image is to the original.
• Resolution is the dots per inch (dpi) that can be detected by the
scanner hardware. A 600 dpi scanner has 600 photocells per
linear inch.
• Bit depth usually 24 bits
Capacity
• Little internal buffering, rely on techniques to transfer the data.
• Storage can be high e.g. A4 page at 600 dpi requires 33.28MB
for 8 bit and around 100MB for full colour.
Cost
• Dropped dramatically in recent years
• Bundled software often the major selling point.
Slide 12
Input & Output Peripherals
Sound
Naturally Occurring Sound
• Natural sound is analogue in form
• To input sound to a computer
• Software samples the incoming signal
• Coverts the signal into digital form
• Usually compresses the file
• This is called ADC – Analogue to Digital Conversion
• Simplest input device is a microphone with sound card but sound
files can be taken from a CD and downloaded from the Internet.
• Sound card performs the ADC and compression
Slide 13
Input & Output Peripherals
Sound sampling
Sampling
Sampler listens to sound
repeatedly and stores a
number representing the
amplitude each time
Sampling Rate
No of times per second sampler listens to the sound e.g. 22
kHz is 22,000 times a second
Sample Size
No of bits stored per sample e.g. 8 or 16 bit samples
Compression
Reduce storage space and reduce quality
Slide 14
Input & Output Peripherals
Sound
Accuracy
• Resolution – Three sampling resolutions in common use.
• 11.025 KHz (8-bit) – voice quality
• 22.05 KHz (8-bit) – Quality of AM radio
• 44.1 KHz (16-bit) – CD quality stereo [data sampled 44,100
times per second]
• Bit-Depth
• 8-bit sample size can hold 256 amplitudes per sample
• 16-bit sample size can hold 65,536 amplitudes per sample
Capacity
• No built-in cache. Depends on fast access via the sound card to
hard disk storage. 10.09MB to store 2 mins stereo audio.
• Compression required e.g. reduce sample rate / size or use a
compression technique to reduce file size.
Slide 15
Input & Output Peripherals
Video
Video Digitising
• is performed by special video digitising circuitry installed
on the motherboard of the computer.
• After market video cards can be purchased to enhance
video.
• File Formats
• Quick Time
• MPEG
• AVi
Slide 16
Input & Output Peripherals
Video
To playback video on a standard computer it will need to be
decompressed by hardware or software, usually on the video card.
Standards
• AVI – (Audio Video Interleave) or Video for Windows. Being
replaced by Active Movie which will playback AVI, QuickTime
and MPEG.
• QuickTime – CODEC s/w developed by Apple but used by both
Mac and PC.
• MPEG – Video board uses hardware to make compression much
faster.
Accuracy – Depends on Compression Technique, frame rate and
resolution.
Speed – Hardware must be fast enough to cope with stream of data to
memory and to the hard disk.
Cost – Not only card but good Multiscan Monitor required (17” and
19” nowadays)
Slide 17
Input & Output Peripherals
Digital Camera
Film replaced by an array of photosensitive cells.
• Images stored electronically using photosensitive diodes
called charge coupled devices (CCDs)
• Intensity of light recorded in an image.
• Analogue values converted to digital using ADC
Compression usually takes place.
• Bit map files turned into JPEG
Image transferred to computer
• Serial Cable or USB
• “Floppy Disk” adapter
• Can then be printed, e:mailed etc.
Slide 18
Input & Output Peripherals
Digital Camera
Accuracy
• Resolution
• Measured in pixels or mega pixels – the more the better. E.g.
640 x 480 pixels or in megapixel mode 1280 x 960.
• Accuracy depends on the array of photosensitive cells.. The
more sensors and the smaller they are the higher the
resolution.
• Bit Depth
• Number of bits in proportional to the number of colours that
can be represented.
Capacity
• Based on resolution and memory in the device.
• Compression v altering resolution
Cost
• Dropping as they become more common.
• Resolution main factor and also facilities (zoom, flash etc.).
Slide 19
Input & Output Peripherals
Printers – Inkjet Printer
Ink-jet Printers are based on one of three different types of
technology: continuous flow ink-jet, liquid ink-jet or phasechange ink-jet. We will look at how a liquid ink-jet printer works.
Liquid ink-jet or bubble-jet, operates by squirting tiny droplets of
ink onto the page. The ink is first heated by passing an electric
current through a coil. In milliseconds a bubble of vapour
appears, forcing a tiny drop of ink from the nozzle onto the paper.
Resolution is typically 600 to 1200 dots per inch, 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 15 pages
per minute, depending upon the model.
Slide 20
Input & Output Peripherals
Printers – Laser Printer
This type of printer uses lasers to "write" a page image onto a
special drum as an electrostatic charge. The charged drum attracts
toner particles which are transferred to the page and heated to set the
image. Usually a page is composed in the printer (often PostScript).
Capacity
On board RAM & processor needed to compose pages. The
more RAM the higher quality graphics can be printed.
Resolution
1200 dpi quite common (600 cheaper, 1200 expensive)
Speed
The faster in pages per minute (ppm)
the dearer ranges from 30 ppm to 50
ppm with 20 ppm being about
average.
Slide 21
Input & Output Peripherals
Multiscan Monitor
The CRT is the basis of most visual display technology. (slowly
shifting)
The screen is arranged as a series of lines of dots and each dot is made
up of three small areas of red, green and blue called a triad. The
intensity of light shone on each triad determines the actual colour of the
pixel.
The picture is redrawn between 50 and 100 times a second. This is the
refresh rate.
A monitor which operate at different refresh rates is known as a
multiscan or multisync monitor. The refresh rate is controlled by the
video adapter.
Screen resolution is quantified by the dot pitch, the distance between
the dots on the screen. Typically this is between 0.28 and 0.38mm,
corresponding to 100 to 70 dpi.
Slide 22
Storage Devices
Magnetic
Magnetic storage devices include hard disks, floppy disks, Zip disks
and magnetic tape.
They are called magnetic storage devices because their recording
surfaces are coated with a material that responds to magnetic fields to
enable data to be stored.
Storage devices can be fixed or removable.
Removable storage devices allow the user
to disconnect the device and physically
transport data from one computer to
another.
Varieties of removable devices include the
Iomega and Syquest hard disks and Jaz
cartridges.
Slide 23
Storage Devices
Magnetic Disk
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
• Rotational speed of hard disks has improved, from 3000 (rpm)
of early disks, to current rotational speeds of 5,400 and even
7,200 rpm.
• Performance is also measured in terms of the rate of data
transfer from the disk.
• SCSI - transfer rate 5Mb/sec
• Ultra Fast SCSIIII transfer rates - 40 Mb/sec.
Slide 24
Storage Devices
Magnetic Disk
Capacity
Hard disks have improved tremendously in their capacity to store
data in the last 10 years. From the modest 10Mb disks of the early
80s to current 1+ Tbyte disks on many of today’s PCs.
Access
The hard disk is a direct access device, meaning that data can be
directly read or written to any portion of the disk.
Slide 25
Storage Devices
Magnetic Tape
Storing data on tapes used to be the only solution to backing up large
capacity hard disks. Now, with large, removable magnetic disks and
optical CR-RW technology, this is no longer the case.
However, removable storage media is comparatively expensive
costing 10 times tape. Therefore tape is still widely used.
Tape is read and written on a tape drive. Data is written to tape in
blocks with inter-block gaps between them. A single operation writes
each block
Data is stored on magnetic tape as magnetised regions on the
surface of the tape induced by the magnetic recording head. To read
data, the tape passes under the read/write head and the stored
magnetised regions produce very small voltages in the head, leading
to a current in the head coil. This current can be analysed to give a
representation of the stored binary data.
Slide 26
Storage Devices
Magnetic Tape
Capacity
Magnetic tapes have large capacities, reaching up to several hundred
gigabytes and come in a variety of sizes and formats.
Since their introduction, tape drives have passed through many stages of
improvement with extremely reliable Digital Audio Tape (44.1 kHz, 16bit record and playback DAT) drives representing the current state of the
art. A 4mm DAT tape can now store up to 240 Gbytes of data!
Access
Tapes are sequential access devices. Accessing data on tapes is therefore
much slower than accessing data on disks.
They are not suitable as storage media for applications where data needs
be used regularly - where a disk is a more appropriate medium. Because
tapes are so slow, they are generally used only for long-term storage and
backup.
Slide 27
Storage Devices
Optical Storage
CD-ROM
A plastic disk is
scanned using a laser. It
reflects off pits on the
surface differently from
lands (bumps)
Re-writeable CD-ROM
is now very common
with re-writeable
DVD’s also now
available.
Capacity – About 650Mb
Speed – from single (150KB/sec) to
32x (or even 40x). The x refers to the
times faster than CD Audio.
Cost – CD-ROM Drives fairly cheap .
Access – Always random
Slide 28
Storage Devices
Magneto Optical Storage
Based on a combination of magnetic and optical technologies.
Active layer is magnetic material.
Recording – magnetic material heated beyond a particular
temperature by laser, allows magnetisation to be
reversed.
Reading – laser operates at much lower temp and reflected beam
rotated by magnetic field and detected by read head.
Capacity – 3.5” disks of 128, 230 and 384 Mb
Speed – Varies as multiple of standard single speed
Cost – decreasing all the time as different formats and capacities
become available.
Slide 29
Storage Devices
Solid State Storage Devices (SSSD)
Solid-state storage devices are made up entirely from electronic
components i.e. they have no moving parts.
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.
Slide 30
Selecting hardware to match
operational requirements
When given a scenario like setting up a System you have to consider:RAM requirements
• Memory must be enough to run the software and support all
the data in the system.
Backing Storage
• Big enough to hold the O/S, Applications and data.
Processor Performance
• Usually as fast as you can afford but must be fast enough to
support all the applications recommended.
Peripherals
• Specify type of printer, monitors etc.
Communications
• Attached to a network or set up a new network. Internet
connection (broadband?)
Slide 31