PERSONAL COMPUTERS

PERSONAL COMPUTERS

The components of a personal computer (PC) are divided between those that are designed to be handled by the user—peripheral devices—and those that would be damaged or dangerous if exposed. Peripheral devices typically perform the function of input (keyboard, mouse, microphone, and camera), output (monitor and speakers), or external storage.

The system case/chassis houses the internal components. These include the motherboard, central processing unit (CPU), system memory modules, adapter cards, fixed disks, and power supply unit. Most cases use a tower form factor that is designed to be oriented vertically and can be placed on a desk or on the floor.

PCs can also be purchased as all-in-one units. All-in-one means that the internal components are contained within a case that is also a monitor.

To perform PC maintenance, you must understand how to open a desktop computer’s case.

A tower case has a side cover that can be removed by sliding the panel from its housing. Cases might be secured by screws or retaining clips and might have anti-tamper security mechanisms. Always refer to the system documentation, and follow the recommended steps.
The front panel provides access to the removable media drives, a power on/off switch, and light- emitting diodes (LEDs) to indicate drive operation. The front cover can be removed but may require the side panel to be removed first to access the screws or clips that secure it.

Features on the front of a typical PC case. (Image © 123RF.com)

The rear panel provides access to the power supply unit (PSU) sockets. The PSU has an integral fan exhaust. Care should be taken that it is not obstructed, as this will adversely affect cooling. There may be an additional case fan.

Features on the rear panel of a typical PC case. (Image © 123RF.com)

Below the PSU, there is a cutout aligned with the motherboard’s input/output (I/O) ports. These allow for the connection of peripheral devices. The spaces between the ports are covered by an I/O shield

At the bottom of the rear panel there are cutout slots aligned with the position of adapter card slots to allow cables to be connected to any I/O ports on the cards. These slots should either be covered by an adapter card or a metal strip known as a blanking plate.

The I/O shield and blanking plates are necessary to prevent gaps in the system case. Gaps create the following problems:

Dust can enter the case and settle on the components, increasing the risk of damage through overheating.
Components are more exposed to touching, increasing risks from electrostatic discharge (ESD). ESD means that a static charge on someone’s finger or on a tool is conducted into a computer chip. This can cause a temporary or permanent fault in the chip. Pins in the I/O shield connect the external metal parts of the ports to the metal case, which in turn is bonded to the PSU, which connects to the building’s ground system when plugged in. This provides a safe path for ESD to drain into, rather than flashing over into a chip.
Components are more exposed to electromagnetic interference (EMI). EMI is energy from magnetic and electrical sources, such as motors or other electronic devices and radios, that can cause temporary or permanent faults. The PC’s case absorbs this energy, but gaps can reduce this protection.

PERIPHERAL DEVICES

An input/output (I/O) port allows a device to be connected to the PC via a peripheral cable. Some ports are designed for a particular type of device, such as a graphics port to connect a monitor. Other ports support a variety of device types. External ports are positioned at the rear or front of the PC through cutouts in the case. They can be provided on the motherboard or as an expansion card.

Interfaces, Ports, and Connectors

A hardware port is the external connection point for a particular type of bus interface. A bus allows the transfer of data to and from devices. The connector is the part of a peripheral cable that can be inserted into a port with the same shape or form factor. Each bus interface type might use multiple connector form factors. Most connectors and ports now use edge contacts and either have an asymmetric design called keying to prevent them from being inserted the wrong way around or are reversible.

Binary Data Storage and Transfer Units

When comparing bus interfaces, it is important to use appropriate units. Computers process binary data. Each binary digit or bit (b) can have the value one or zero. Storage is often measured in multiples of eight bits, referred to as a byte (B). A lowercase “b” unit refers to a bit, while uppercase means a byte.

Transfer rates are expressed in units per second of the following multiples of bits and bytes:

• 1000—Kilobits (Kb/s or Kbps) and kilobytes (KB/s and KBps).
• 1000×1000—Megabits (Mb/s) or megabytes (MB/s).
• 1000x1000x1000—Gigabits (Gb/s) and gigabytes (GB/s).