Computer Hardware: Serial and Parallel Data Transfer

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Serial and Parallel are the two methods used to transfer data between computer terminals. Serial takes at least ten times (eight data bits, plus start and stop) longer to transmit one character along a cable than parallel, but is a considerably less expensive way of doing it. Serial data transmission which uses the RS232 serial ports on a PC sends or receives data one bit at a time in a continuous stream. Each character is made up of eight bits (ASCII format). To enable a serial character to be correctly recognised it begins with a start bit (LOW) followed by eight character bits and finally a stop bit (HIGH), a total of ten bits, requiring ten clock periods for the transfer of one character. The USB port is also a serial transfer method. Parallel transmission is through a minimum of eight identical cables. In practice there are additional links for handshaking (control) purposes. Parallel transmission is ten times faster than serial. Because of the multi-core cables required it’s more expensive which restricts it to short distances i.e. PC to printer is a good example. Data transfers across parallel cabling systems is usually done in standard binary format where a HIGH is measured as 5V and LOW as 0V. However, for serial transmission, over considerably longer distances by cable or even longer by satellite or fibre optics the data is converted to some other method using audio tones, radio signals or infrared light.

DATA STRUCTURES: Data Sorting. Interactive Content! A number of methods are used in the process of sorting data. Here we introduce one such technique, the ‘bubble sort’ where the sorted values move to the top or bottom of the sorted array, depending on the ascending or descending selection. The time taken to complete the sort depends on how the original data is arranged and the number of array interchanges to be made. The data to be sorted could originate from a list of data items (these could be names) in a disk file where to speed up the process it’s copied into an array. An array is a group of RAM locations that the central processor operates on. Once sorted the data can then be copied back to the original file. The process is as follows. Compare each consecutive pair of data items, if the value of position(n) in the array is greater or less than the position(n + 1), (depending on the ascending or descending selection) then exchange that pair. Repeat for the next pair and so on, looping back to the beginning until the sort is completed. It’s not possible to show all the intermediate sorting as the number of exchanges increases significantly for larger numbers of items in the array. If you follow through the first few exchanges you will quickly get a feel of how it works.

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