What is a peripheral

Peripherals are physical electronic devices that allow the computer to interact with the outside world. Systems that store or archive information are also considered peripheral.

Peripherals are all the devices that help the computer to interact with its exterior, meaning the mouse, keyboard, screen, printer and others. The word peripheral means additional but not essential, although today almost all peripherals are essential.

Peripherals allow you to perform input/output (I/O), storage, or communication operations. A peripheral can be connected to one of the ports that a computer has. Peripherals are considered part of the computer hardware, but not all hardware used by the computer is considered a peripheral.

There are 3 ways to control a peripheral:

1-Programmed Input/Output: The start of the I/O operation is performed at the initiative of the CPU depending on the program being executed. There are two variants:
a) Programmed I/O without status query: The CPU decides when the transfer takes place, so the device must always be ready to receive data (S) or send it (E).
b) Scheduled I/O with status query (Polling): Before performing an I/O operation, the CPU reads the status of the controller to check if the device is ready.

2-Interruptions: Through this technique, peripherals are allowed to act independently and interrupt the processor when there is any data or data block to be transmitted to or from memory.

3- Autonomous management of peripherals (DMA): Peripherals have direct access to memory and once the processor assigns them a task, they execute it completely independently, indicating to the
processor, through an interrupt mechanism, the end of the assigned task.


Below is a summary of how peripherals are classified, for more information and to see examples click on each item:

1.- Input peripherals: They allow data to be entered. They transform external information (instructions or typed data) according to one of the input/output codes.

2.- Output peripherals: They show the information to the outside of the computer. It transforms the information found inside the computer into written characters intelligible by the user.

3.- Storage peripherals: They store data and information. They transform external information into encoded signals, allowing their automatic transmission, detection, interpretation, processing and storage.

4.- Communication peripherals: They allow communication with other machines or computers.

The devices that make up the core of the computer are not peripheral, let us remember that they are three components of the heart of a computer: The CPU, central memory and the I/O subsystem.

It must be taken into account that there are auxiliary equipment used for a certain computer service, which are not peripherals. These equipments are not physically connected to the computer, their operation is independent from it and they serve to prepare or help in the preparation or use of the information that is given to, or produced in a computer. An example is the equipment used to record magnetic tapes manually through a keyboard.

Neither are units or devices that serve to support information, that is, those physical media on which the information goes, considered peripheral. For example floppy disks or cds.

The general characteristics of the peripherals are:

Reliability: It is the probability that an input/output error will occur and depends on the nature of the support (there are supports that are much less reliable than others), the environmental conditions in which the support is stored, or the characteristics of the Unit.

Duration: It is the permanence without alteration of the data over time. Some supports lose the written signal over time and end up losing the data due to physical obsolescence of the support.

Density: It refers to the amount of data (bits or characters) contained per unit of volume, surface or occupied length.

Reuse: An information support is said to be reusable when it allows us to save new information on data that is already obsolete. Manufacturers of optical disks (CD-ROM) have been faced with this problem, which until recently have not been capable of being reusable.

Type of access: Feature linked to the reader/writer device. A device is said to have sequential access if, in order to access a given piece of data, we must first access all those that physically precede it (Example: magnetic tapes). On the other hand, it is said that a device allows direct access if we can access data without having to go through the data that precedes it (Example: magnetic disk).

Transportability: We say that an information medium is transportable if it can be moved from one peripheral unit to another. Example: the diskette can be used in different diskette drives of the same format. On the contrary, there are fixed information supports, which cannot be extracted from the corresponding unit. (Example hard drive).

Each peripheral is usually made up of two clearly differentiated parts in terms of their mission and operation: a mechanical part and an electronic part.

The mechanical part is basically made up of electromechanical devices (manual switches, motors, electromagnets, etc.) controlled by electronic elements. The operating speed of a peripheral is based on the mechanical elements.

The electronic part is mostly included in the interface circuits.

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