A Level Computing for AQA Teacher’s Resource CD-ROM 20 CHAPTER: Communication methods Serial and parallel communications, bandwidth, bit rate and baud rate

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Communication Communication is the process of transmitting data and instructions between: –the processor, memory and the I/O controllers –the computer and the peripheral devices –one computer and another computer on a local or global network.

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Serial communication Serial communication means sending data one bit at a time in sequence. It is used for most communications over 1 metre, including transmission of data around local and global networks. High transmission rates can be achieved through: –USB, which provides high speed data cabling from peripherals –network cables, which transmit at 100Mbps (Megabits per second).

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Parallel communication Parallel communication uses a number of parallel wires, so that more bits can be transmitted simultaneously. It is only used over short distances, as the wires are expensive to produce, the signal degrades over distance and synchronising the data down each wire can be complex. It is mainly used inside the computer in microscopic form in: –data, address and control buses –the internal architecture of the processor.

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Serial and parallel compared

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Bandwidth Bandwidth is the term that describes the amount of data that can be transmitted along a communication channel. It relates to the range of frequencies that can be used to carry data. The greater the range of frequencies, the greater the volume of data that can be transmitted within a given time-frame. Bandwidth is measured in bits per second (bps), which is how many binary digits it can send each second. Measurements are usually recorded in Kilobits per second (Kbps) or Megabits per second (Mbps).

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Examples of bandwidth Bandwidth has become a vital measure in assessing the speed of access to the Internet. A 28.8Kbps modem will transmit and receive data at up to 28,800 bits per second. A 56Kbps modem has twice the bandwidth and will transmit twice as much data in the same time frame. Broadband technology claims rates of 1Mbps which, in theory, is 20 times faster than normal dial-up access.

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Bit rate Bit rate is the term used to describe the speed at which a particular data transmission is taking place. It is closely linked to bandwidth, as bit rate is limited to the bandwidth available. It is measured in bits per second (bps) and is the actual rate of transmission. A 56k modem has a bandwidth of 56Kbps, but the bit rate is probably around 45Kbps. This is because not all the bits are being used to transmit data – some bits are parity bits or start/stop bits.

A Level Computing for AQA Teacher’s Resource CD-ROM © 2005 Bob Reeves, Dave Fogg/Hodder Murray Baud rate Baud rate is another measurement of the speed of data transmission. One baud represents one electronic state change in frequency on the carrier wave. Therefore, one baud roughly equates to one bit per second. Baud measurements were used before the widespread use of the Internet. It is sufficient to state that one baud per second is the equivalent of one bit per second.