AI+A11Y 11MAY2024 HYDERBAD GAAD 2024 - HelloA11Y (11 May 2024)
Hcs Topic 3 Peripherals V2
1. Topic 3 Peripherals 3.1 Interfaces 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 such as disk drives, printers etc. work in different ways and linking a peripheral to the processor is a difficult task.
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3. 1. Buffering 3. Voltage conversion 4. Protocol conversion 2. Data format conversion Interface functions 5. Status signal handling An interface will have to perform many of the functions listed below. This will vary depending on the characteristics of the device. (jobs)
4. 1. Buffering 3. Voltage conversion 4. Protocol conversion 2. Data format conversion 5. Status signal handling Buffering Processors can send data at a faster rate than most peripherals can deal with it. 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.
5. 1. Buffering 3. Voltage conversion 4. Protocol conversion 2. Data format conversion 5. Status signal handling Data Format conversion 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. Two common format conversions required are: Serial to parallel Analogue to digital
6. 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.
7. 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.
8. Analogue to digital Signals being received by a modem on a telephone line. Recording using a microphone. An interface performs the data format conversion. 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:
9. 1. Buffering 3. Voltage conversion 4. Protocol conversion 2. Data format conversion 5. Status signal handling Voltage Conversion 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.
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12. Interfaces - current trends Current common interface standards include: USB Firewire Bluetooth www.en.wikipedia.org/wiki/Firewire www.electronics.howstuffworks.com/bluetooth.htm/printable www.usb.org
13. Universal Serial Bus (USB) This is now a very common interface for use with printers, scanners, digital cameras and it can also be used for keyboards and mice. www.usb.org 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 2 transfer speed 480 megabits per second. USB 1 transfer speed 12 megabits per second.
14. www.en.wikipedia.org/wiki/Firewire Firewire IEEE 1394 i Link 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. 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. It can supply modest power services to devices. aka aka
15. Bluetooth It transmits very weak signals on a 2.45 gigahertz frequency for communication over short distances, typically up to 10 metres. Bluetooth is a wireless technology which is used for computers, PDAs, mobile phones, headphones, mice and keyboards. Bluetooth transfer speed up to 1 megabit per second. www.electronics.howstuffworks.com/bluetooth.htm/printable www.electronics.howstuffworks.com/bluetooth.htm/printable
16. serial port: 115kbits/s standard parallel port: 115kBYTES/s IDE: 3.3-16.7MBYTES/s SCSI-1: 5MBYTES/s SCSI-2 (Fast SCSI, Fast Narrow SCSI): 10MBYTES/s Fast Wide SCSI (Wide SCSI): 20MBYTES/s Ultra SCSI (SCSI-3, Fast-20, Ultra Narrow): 20MBYTES/s UltraIDE: 33MBYTES/s Wide Ultra SCSI (Fast Wide 20): 40MBYTES/s Ultra2 SCSI: 40MBYTES/s Wide Ultra2 SCSI: 80MBYTES/s Ultra3 SCSI: 80MBYTES/s Wide Ultra3 SCSI: 160MBYTES/s Other standard interfaces include the following: These are mainly used for Hard drives and other internal peripherals.
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22. Input devices 3 Sound Card A sound card takes an analogue sound and converts into a digital one. The sound is sampled by listening and measuring the sound every n th 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.
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32. Buffers & Spoolers 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
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46. Backing Storage devices 4 Solid State storage Solid state storage devices have no mechanical or moving parts and use integrated circuits rather than magnetic or optical media. Current technology means that capacity is lower than magnetic or optical media but costs are falling and capacities are increasing. Data transfer takes place at very high speeds and the devices are very robust . Flash cards are a popular form of solid state storage and are commonly found in digital cameras and mobile phones .
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49. Development trends in Backing Storage devices & media 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 Capacities for all devices are increasing and cost per byte is falling . HD-DVD.