☎️Methods

Serial Vs Parallel

Computers can transmit data between each component in two different ways: serially or as parallel.

Serial Transmission

This is when data is sent one bit at a time, one after another thought a single .

Serial transmission is usually used for medium to long distances (usually for communications over 2m). They are usually used for hardware peripherals such as mouse and keyboards.

In this type of communication, only one line is needed to send data in one direction. Two lines will be required for two-way communication.

Parallel Transmission

This is when multiple communication lines are used to send multiple bits between components simultaneously.

The more lines a parallel communication medium uses, the more bits can be transferred simultaneously. In this type of communication, double number of lines are needed for two way communication.

Each communication line in the parallel communication medium will have slightly different electrical properties. This means that the time it takes to completely transmit a single bit may vary from line to line, meaning that bit sent together may not be received together, thus causing the problem of skew.

The longer the communication line distance, the worser the skew gets. In some cases, data from different pulses may overlap, which can corrupt the data. Also parallel communication mediums are more expensive as they have multiple lanes. This is why parallel data transmission is usually used over short distances such as between parts of the CPU and within RAM.

Another problem with parallel communication is known as crosstalk. This is when lines are tightly packed, and electromagnetic interferences incur between adjacent parallel wires which can corrupt the data. This becomes worse as the frequency (speed of transmission) increases.

Why serial > parallel

Since serial communication doesn't suffer from problems such as crosstalk and skewing, it is more reliable, especially for long distance. Also, serial communication uses just one line, thus making it cheaper.

Synchronous Vs Asynchronous

In synchronous transmission, a clock signal is used to time when signals are sent (shared both by sender and receiver). These are used by the busses in the computer's processor during the fetch-decode-cycle.

The signals are sent as regular intervals, and they are received in the same order they are sent in. This makes synchronous data transmission suitable for transmitting info in real time systems.

On the other side, asynchronous uses start and stop bits to indicate the duration of a transmission, this means that no shared clock signals are required.

The start bit can either be 0 or 1, however it must be the opposite of the stop bit.

Also, a parity bit may be added for error detection.

This type of communication is useful in systems where maintain constant clock signal is difficult.

A disadvantage of asynchronous transmission is that it is relatively slow owing due to the number of bits being sent. However, It is cheap and effective form of serial transmission, well suited to low speed connections such as keyboard and mouse.

Keywords

Symbol — Pattern of bits represented by a signal. E.g. the symbol for 4 bits can be 1101.

Baud rate — Number of signal changes in the medium per second. 1 Baud (1Bd) is equal to 1 symbol change per second.

Bit rate — Number of bits transmitted over the medium per second. Usually measured as bits per second (bps).

Therefore, a communication system’s bit rate is equal to its Baud rate multiplied by the number of bits per signal in the communication medium.

Bit Rate = Baud Rate × Number of bits per signal

A communication medium’s bit rate will be higher than its Baud rate if there is more than one bit sent per signal.

Bandwidth — Describes the range of frequencies that a communication medium is capable of transmitting. There is a direct relationship between bandwidth and bit rate. Higher bandwidth results in higher bit rate.

Protocol — Set of rules relating to communication between devices, Internations organisation decide them so that different devices, made by different manufacturers, are enabled to communicate with one another.