Transcript 2. Data format conversion - Sabbir Saleh

Computer peripherals such as disk drives, printers etc. work in
different ways and linking a peripheral to the processor is a
difficult task.
They work at different speeds, use different codes, transfer
different amounts of data at a time, and even work at different
voltages.
An interface is the hardware and software needed between a
processor and a peripheral device in order to compensate for
differences in their operating characteristics. The interface
allows the two devices to communicate correctly.
Computer Peripherals and Interfacing
1
An interface will have to perform many of the functions (jobs)
listed below. This will vary depending on the characteristics of
the device.
1. Buffering
2. Data format conversion
3. Voltage conversion
4. Protocol conversion
5. Status signal handling
Computer Peripherals and Interfacing
2
Processors can send data at a faster rate
than most peripherals can deal with it.
1. Buffering
2. Data format conversion
3. Voltage conversion
4. Protocol conversion
5. Status signal handling
e.g. an inkjet printer is a mechanical device. It takes time to
spray the ink, physically move the paper etc.
Many interfaces have a buffer to store data. A buffer is an
amount of RAM in the peripheral device which is used to store
data until the device is able to process it.
It allows the processor to send data at high speed and then
continue with other tasks while the device can work at its own
slower pace to complete the task.
Computer Peripherals and Interfacing
3
The processor and the peripheral
device may format data in different
ways and so the interface may have to
convert the format of the data.
1. Buffering
2. Data format conversion
3. Voltage conversion
4. Protocol conversion
5. Status signal handling
Two common format conversions required are:
Serial to parallel
Analogue to digital
Computer Peripherals and Interfacing
4
Serial to parallel
Serial transmission is where data is sent along a single
line one bit at a time.
Parallel transmission is where data is sent several
bits a time along multiple lines.
The processor uses parallel transmission but many
devices send and receive data serially so the data
format has to be converted.
Computer Peripherals and Interfacing
5
Comparing Serial and parallel in terms of performance
Parallel is faster over short distances
When data is sent over longer distances in parallel
the data can fall out of alignment and so becomes
corrupted. This known as “skew”
Serial transmission is more efficient when longer
distances are involved.
Computer Peripherals and Interfacing
6
Analogue to digital
The processor is a digital device and works with digital signals.
Some devices sense analogue signals and so these signals
have to be converted into digital signals for processing.
Examples of analogue signals would include:
Signals being received by a modem on a telephone line.
Recording using a microphone.
An interface performs the data format conversion.
Computer Peripherals and Interfacing
7
1. Buffering
2. Data format conversion
3. Voltage conversion
4. Protocol conversion
5. Status signal handling
Most peripherals work with higher voltages than the processor.
These voltages have to be altered to allow communication to
take place.
e.g. a keyboard generates 9 volt signals.
This voltage has to be reduced to a 5 volt signal before it
can be handled by the processor.
An interface performs the voltage conversion.
Computer Peripherals and Interfacing
8
1. Buffering
2. Data format conversion
3. Voltage conversion
4. Protocol conversion
5. Status signal handling
When two devices want to communicate they need to agree
on a set of rules for effective communication to take place.
These sets of rules are called protocols.
The protocols will set out rules such as:
•
Speed of data transfer
•
Voltage levels
•
Size of data units e.g. 7 bit or 8 bit transfer.
The interface makes sure that data is sent/received
according to the agreed rules.
Computer Peripherals and Interfacing
9
1. Buffering
2. Data format conversion
3. Voltage conversion
4. Protocol conversion
5. Status signal handling
A peripheral device interface stores information about the
current state of the device itself.
Examples of status signals would include:
•
•
•
off-line Not ready to receive data
busy
Buffer full – not able to receive data
ready On-line and ready to receive data.
The processor and the interface communicate before data is
sent to make sure that the device is ready to send/receive.
Computer Peripherals and Interfacing
10
Current common interface standards include:
USB
www.usb.org
Firewire
www.en.wikipedia.org/wiki/Firewire
Bluetooth
www.electronics.howstuffworks.com/bluetooth.htm/printable
Computer Peripherals and Interfacing
11
www.usb.org
This is now a very common interface for use with printers,
scanners, digital cameras and it can also be used for
keyboards and mice.
It allows “hot swapping” which means that you can plug and
unplug it while the computer is on.
You can attach up to 128 USB devices at the same time using
hubs in a “daisy chain”.
The USB connection also provides power to the devices.
USB 1 transfer speed 12 megabits per second.
USB 2 transfer speed 480 megabits per second.
USB 3 transfer speed 640 MegaBytes per second.
12
aka
aka
www.en.wikipedia.org/wiki/Firewire
This is the standard interface for use with digital video
camcorders, some storage devices and the first Apple Ipod.
It allows hot swapping and up to 63 Firewire devices can be
connected at the same time.
It can supply modest power services to devices.
FireWire 400 transfer speed 400 megabits per second.
FireWire 800 transfer speed 800 megabits per second.
IEEE 1394b transfer speed 3.2 gigabits per second.
Computer Peripherals and Interfacing
13
www.electronics.howstuffworks.com/bluetooth.htm/printable
Bluetooth is a wireless technology which is used for computers,
PDAs, mobile phones, headphones, mice and keyboards.
It transmits very weak signals on a 2.45 gigahertz frequency
for communication over short distances, typically up to 10 metres.
Bluetooth transfer speed up to 1 megabit per second.
Computer Peripherals and Interfacing
14
Other standard interfaces include the following:
serial port:
standard parallel port:
IDE:
SCSI-1:
SCSI-2 (Fast SCSI, Fast Narrow SCSI):
Fast Wide SCSI (Wide SCSI):
Ultra SCSI (SCSI-3, Fast-20, Ultra Narrow):
UltraIDE:
Wide Ultra SCSI (Fast Wide 20):
Ultra2 SCSI:
Wide Ultra2 SCSI:
Ultra3 SCSI:
Wide Ultra3 SCSI:
115kbits/s
115kBYTES/s
3.3-16.7MBYTES/s
5MBYTES/s
10MBYTES/s
20MBYTES/s
20MBYTES/s
33MBYTES/s
40MBYTES/s
40MBYTES/s
80MBYTES/s
80MBYTES/s
160MBYTES/s
These are mainly used for Hard drives and other internal
peripherals.
Computer Peripherals and Interfacing
15
For the Higher course you need to be aware of how peripherals
work and of the current specifications and trends.
pctechguide.com
howstuffworks.com
You should be aware of the following characteristics for each
type of device:
•
•
•
•
•
resolution
speed
capacity
cost
type of interface
Computer Peripherals and Interfacing
16
Keyboards generally follow the standard Qwerty layout
although new innovative designs are available which attempt
to improve user comfort and ease of use.
•
•
resolution n/a(not applicable)
speed
Speed of input is determined by the user’s typing
ability. This is always very slow in computer terms
and so speed is not a performance issue.
Computer Peripherals and Interfacing
17
•
capacity
A keyboard has a very small buffer to store several
keypresses but again capacity is not particularly relevant
for keyboards.
•
cost
Keyboards are inexpensive items with prices ranging from
£8 up to £50 and more for more stylish models.
Manufacturers include Microsoft, Logitech and Benq.
•
type of interface
The PS2 interface was the standard but USB, Bluetooth
and infra red are becoming more common.
Computer Peripherals and Interfacing
18
Scanners are used to convert graphic images into a digital
format suitable for processing in a computer.
Text can also be input when the scanner is used with Optical
character recognition (OCR) software.
• resolution
The resolution of a scanner is measured in dots per inch
(dpi). Note that 600 dpi means that every square inch has
600 x 600 dots = 360000 dots.
The bit depth also affects quality with modern scanners
offering 48 bit depth.
Computer Peripherals and Interfacing
19
•
speed
The speed of a scanner is measured by how long it takes
to scan a page at a particular resolution and bit depth.
•
capacity
•
cost
Scanners cost from £50 to £300 depending on features.
Manufacturers include Canon and Epson.
•
type of interface
The USB 2 interface is the standard with SCSI and
Firewire also available.
n/a
Computer Peripherals and Interfacing
20
A sound card takes an analogue sound and converts into a
digital one. The sound is sampled by listening and measuring
the sound every nth fraction of a second and storing the
sample as a digital number.
The sampling rate determines how often per second a sample is
taken. CD quality samples at 44.1 kHz = 44,100 times per
second.
The sample size/bit depth determines the range of sounds
which can be recorded each time. CD quality works at 16 bit
depth which gives a range of 65,536 different sounds.
Computer Peripherals and Interfacing
21
•
speed n/a
•
capacity n/a
•
cost
Sound cards cost from £10 to £200 depending on features.
Manufacturers include Creative Labs and Terratec.
•
type of interface
The PCI interface is the standard with USB and Firewire
also available.
Computer Peripherals and Interfacing
22
A digital camcorder takes moving images and converts them
into a series of individual digital images.
A CCD(Charge coupled device) detects light intensity and
converts it into an electrical signal.
• resolution
The number of pixels in the CCD can affect quality.
More expensive models have 3 CCDs, one for each
primary colour, which also improves quality. A high
optical zoom also allows good quality.
Computer Peripherals and Interfacing
23
•
speed
Digital camcorders allow video display at 25 frames per
second following the PAL standard which is used in most
of Europe.
•
capacity
The capacity of a camcorder depends on the type of
backing storage used. These include MiniDV,
Digital8, Hi8 tapes and optical DVD.
•
cost
Costs range from £200 to £3000 depending on features.
Manufacturers include Sony, Canon and JVC
•
type of interface
Firewire is the standard interface for digital camcorders.
Computer Peripherals and Interfacing
24
A digital camera takes a still image and converts it into a
digital image.
A CCD(Charge coupled device) detects light intensity and
converts it into an electrical signal.
• resolution
The number of pixels in the CCD affects quality.
CCDs of 4 megapixels and upwards are now
common. Cameras typically use 24 bit depth for
colour. A high optical zoom also allows good quality.
Computer Peripherals and Interfacing
25
•
speed
Shutter speeds are relevant for taking photographs in
different situations, e.g. sports shots, night scenes.
•
capacity
The capacity of a camera depends on the type of backing
storage used. These include SD, XD, Compact flash
which are all solid state memory cards, and a microdrive
which is a miniature Hard drive.
•
cost
Costs range from £40 to £5000 depending on features.
Manufacturers include Fuji, Olympus, Canon and Nikon
•
type of interface
USB 2 is the standard interface for digital cameras.
Computer Peripherals and Interfacing
26
Tiny droplets of ink are heated and explode onto the page.
Printers can print text and graphics, colour and a range of
greyscales.
• resolution
Resolution is measured in dpi and 4800 x 1200 is
typical. 24 bit depth is commonly used for colour.
•
speed
Printer speed is measured in pages per minute (ppm).
The speed depends on the size of the page and the
complexity of the image being printed.
Computer Peripherals and Interfacing
27
•
capacity
Printers store data about to be printed in a buffer. A large
buffer will allow the user to begin other work on the
computer while the printer is still processing the page.
•
cost
Costs range from £40 to £300 depending on features.
Manufacturers include Epson, Lexmark, Canon &
Hewlett Packard (HP).
Running costs for inkjet printers are very high as cartridges
have a limited capacity and are very expensive
•
type of interface
USB is the standard interface for modern inkjet printers with
older models using serial or parallel interfaces.
Computer Peripherals and Interfacing
28
Lasers 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 fuse the
image onto the paper.
• resolution
Resolution is measured in dpi and 600 x 600 is typical.
Monochrome models are very common in offices and
colour models are coming down in price.
• speed
Printer speed is measured in pages per minute (ppm). The
speed depends on the size of the page and the complexity
of the image being printed.
Computer Peripherals and Interfacing
29
•
capacity
Printers store data about to be printed in a buffer. A large
buffer will allow the user to begin other work on the
computer while the printer is still processing the page.
•
cost
Costs range from £70 to £13,000 depending on features.
Manufacturers include Epson, Lexmark, Canon &
Hewlett Packard (HP).
Running costs for laser printers are low as laser toner
cartridges have a larger capacity than inkjets. Laser toner
for colour lasers however is still very expensive.
•
type of interface
USB, serial, parallel and ethernet interfaces are used for
laser printers.
Computer Peripherals and Interfacing
30
Two techniques are used with printers to cope with the fact
that they work slowly compared to the processor.
These involve the use of buffers and spoolers.
Buffer
You have already met the concept of buffering, using RAM to
store data until the printer is ready to process it. Look back at
slide 3 for more details
Computer Peripherals and Interfacing
31
Spooler
Spooling is a similar technique but here the file to be printed is:
• Sent to the computer’s hard disk for temporary storage.
• Stored in a queue and sent to the printer in stages as a a
background job during the processor’s idle moments.
This can slow down printing but allows the user to carry on with
other tasks while printing is taking place in the background
On our school network every time you print, a spool file is
created and sent to the server for printing.
The server then takes over the job of sending it down to
the printer when the printer is ready.
Computer Peripherals and Interfacing
32
CRT Monitors are large and bulky and use a similar technology
to traditional television sets. The Cathode Ray Tube is the
bulky part which sticks out at the back.
•
resolution
Resolution is measured in dpi and CRT monitors can
display at different resolutions.
The size of the display directly affects resolution. An
image on a 21-inch monitor with an 800x600 resolution
will not appear nearly as sharp as it would on a 15-inch
display at 800x600.
Computer Peripherals and Interfacing
33
The refresh rate is the number of times that the image on
the display is drawn each second. A CRT monitor with a
refresh rate of 72 Hertz (Hz) cycles through all the pixels
from top to bottom 72 times a second.
•
•
•
•
A low refresh rate means that the screen flickers and
this can cause headaches and eye strain.
n/a
speed
capacity n/a
cost
Costs range from £50 to £600 depending on size and
features. Manufacturers include Samsung, Phillips,
Viewsonic.
type of interface
The VGA interface is common with the new DVI digital
interface becoming more popular.
Computer Peripherals and Interfacing
34
Thin Film Transistor(TFT) Monitors use Liquid Crystal
Display(LCD) technology to create monitors which are very
slim and light. These are used on laptops and are rapidly
becoming the standard type of display on desktops.
•
resolution
Resolution is measured in dpi and TFT monitors are built
with a particular resolution for best quality.
Lower resolutions can be set but quality is poor.
1024 x 768 is common for laptop displays. This
requires 2,359,296 transistors etched onto the glass.
Computer Peripherals and Interfacing
35
There is no need to worry about refresh rate or flickering
on a TFT monitor as transistors are either on or off.
Due to manufacturing limitations TFT panels virtually
always have some dead pixels which do not display
correctly.
•
speed
•
•
capacity n/a
cost
Costs range from £100 to £1600 depending on size and
features. Manufacturers include NEC, Sony, LG.
•
type of interface
The VGA interface is common with the new DVI digital
interface becoming more popular.
n/a
Computer Peripherals and Interfacing
36
Hard Disks and floppy disks are the main examples of magnetic
disk with floppy disks rapidly becoming obsolete due to their
limited capacity of 1.44 Mb.
The read/write head moves to the required track and waits
until the requested block spins past the head.
The following characteristics refer to hard disk.
•
resolution
n/a
Computer Peripherals and Interfacing
37
•
speed
Speed of access is important. The main factor
here is the rotational speed of the disk with
typical figures being 5,400 or 7,200 rpm.
(Revolutions per minute) The type of
interface also affects the speed of access.
•
capacity
The capacity of modern hard disks ranges from
500 GB to 2 TB.
•
cost
Costs range from £30 to £160 depending on
capacity and type of interface. Manufacturers
include Maxtor and Seagate.
•
type of
interface
Interfaces include IDE, SCSI, ATA and SATA.
Computer Peripherals and Interfacing
38
These include CD-ROM, CD-R, CD-RW, and their DVD
equivalents.
The disk surface is a mirror covered with billions of tiny lands
and pits that are arranged in a long, tightly wound spiral.
A laser reads and interprets the information as bits of data.
ROMs
R
RW
•
are read only.
can be written to once but not erased.
can be written to and erased using special software.
resolution
n/a
Computer Peripherals and Interfacing
39
•
speed
CD Speed is measured as a multiple of single
speed audio which runs at 150 Kbps. Typical
speed is now x52.
Single speed DVD is 1,250 Kbps and x16 speed
is common.
Speeds for reading and writing differ with
reading speed normally being the fastest.
•
capacity
CD – 650 MB
DVD – Between 4.7 GB and 17 GB depending
on single/double sided, single/double
layered.
Computer Peripherals and Interfacing
40
•
cost
Costs range from £10 to £130 depending on
type and whether the drive is internal or
external. Manufacturers include Pioneer,
Lite-On and NEC.
•
type of
interface
Interfaces include IDE, USB2 and firewire.
Computer Peripherals and Interfacing
41
Magnetic tape drives are still commonly used for backup
purposes although removable magnetic disks and optical RW
technology can now also be used for backups. Tapes have a
higher capacity than any of the optical media is use today.
Tape drives are relatively expensive but tapes are cheap.
The school network backs up all user data files every night at
midnight and five generations are kept.
•
resolution
n/a
Computer Peripherals and Interfacing
42
•
speed
Tapes allow serial/ sequential access and so
their use is generally restricted to making
backups.
Transfer rates range from 2 to 30 Mbps
depending on model and price.
•
capacity
Capacities vary widely depending on model
and price. Data can be stored in a
compressed format which increases capacity
but reduces transfer rates.
Figures up to 1.3 TB were found on
current price lists. (June 2009)
Computer Peripherals and Interfacing
43
•
cost
Costs range from £80 to £6,000 depending
on type, capacity and data transfer rate.
Manufacturers include Seagate, Travan and
Hewlett Packard.
•
type of
interface
Interfaces include IDE, USB and SCSI.
Computer Peripherals and Interfacing
44
Solid state storage devices have no mechanical or moving parts
and use integrated circuits rather than magnetic or optical
media.
Data transfer takes place at very high speeds and the devices
are very robust.
Current technology means that capacity is lower than magnetic
or optical media but costs are falling and capacities are
increasing.
Flash cards are a popular form of solid state storage and are
commonly found in digital cameras and mobile phones.
Computer Peripherals and Interfacing
45
Memory sticks have virtually replaced floppy disks as a
portable storage medium being easy to carry around.
Some even double up as key rings or mp3 players.
•
resolution
n/a
•
speed
With no moving parts, data transfer speeds
are high at up to 480 Mbps using a USB2
interface
Computer Peripherals and Interfacing
46
•
capacity
Capacities vary widely depending on type.
Figures from up to 16 GB were found on
current price lists. (June 2009)
•
cost
Costs vary up to £45 depending on type and
capacity.
Manufacturers include Crucial, Kingston and
Sony.
•
type of
interface
USB 2
Computer Peripherals and Interfacing
47
Capacities for all devices are increasing and cost per
byte is falling.
Solid state storage is replacing floppy disks as the
portable medium.
DVD is replacing CD as the main optical drive in
computer systems.
Blu Ray is now the standard for High definition DVD
technology. It won against its rival HD-DVD.
Computer Peripherals and Interfacing
48