The physical components of a computer are known as hardware. A digital computer is not a single component machine but is made up of the five distinct elements, as shown in the following diagram.
The programmes used in a computer are known as software. INPUT DEVICES
Input devices are the means by which a computer is fed with the information required for problem solving and consist of the following typical hardware:
¾ Keyboard ¾ Scanner
¾ Touch sensitive screen ¾ Speech recognition ¾ Mouse
¾ Joy stick
¾ Data from sensors
As long as the data is identifiable, the computer’s processor is able to recognise it and accordingly routes it along the appropriate internal buses or data lines. These form a network of communication lines that connect the internal elements of the processor and lead to external connectors linking the processor to the other elements of the computer system. The following types of CPU buses exist:
¾ A control bus consists of a line that senses input signals and another line that
generates control signals from within the CPU.
¾ The address bus is a one-way line from the processor that handles the location of data in memory addresses.
¾ The data bus is a two-way transfer line that both reads data from memory and writes new data into memory.
Chapter 17 Computer Technology
CENTRAL PROCESSING UNIT
The Central Processing Unit (CPU) may consist of a single chip or a series of chips that are able to perform arithmetic and logical calculations. It can also control the operations of the other system elements. A microprocessor is a miniature CPU chip, which incorporates additional circuitry and memory. CPU chips and microprocessors consist of the functional sections shown below.
The CPU receives input data and uses that data to carry out specific instructions, from which an output is derived. Typical input data might be wind velocity and direction or even the distance to run to a destination. The CPU then carries out calculations on this data using the following parts to give output data, such as TAS or time to run to the next waypoint.
A central control unit coordinates the functions carried out in each section of the computer via a communication link or data transfer bus. The control unit decodes or reads the patterns of data held in a designated register, or temporary storage area, and keeps track of any instructions. The register also holds the location and results of these operations. The control unit translates the pattern into an activity, such as adding or comparing. It also indicates the order in which individual operations use the CPU and regulates the amount of CPU time that each operation may consume.
Memory is normally divided into either volatile memory, which is lost whenever the computer loses power, or non-volatile memory, which remains in the system until it is over-written with new data. The main types of internal memory are:
RAM (random access memory) is volatile memory. The data deposited in it is lost whenever the power is turned off or alternative states are written in.
ROM (read-only memory) is non-volatile memory and normally contains data that has been inserted on the chip during its manufacture. The ROM typically contains start-up details and mathematical formulae, which are maintained even after the power has been switched off. Replacing the entire chip is the only way to change the instructions on ROM.
Computer Technology Chapter 17
Electrics 17-5
Arithmetic and logic unit (ALU) chips give the computer its calculating capability, allowing both arithmetical and logical calculations using a combination of digital logic circuits. These circuits are used to make specific true-false decisions based on the presence of multiple true-false signals at the inputs. The signals may be generated by either mechanical switches or by solid-state transducers, which are combined together to form an integrated circuit (IC)
OUTPUT DEVICES
The output devices enable the user to see the results of the computer's calculations or data manipulations. The most common output device is the video display screen, which is a monitor that displays characters and graphics on a cathode-ray tube (CRT), or television-like screen, which is usually small. Portable computers commonly use liquid crystal displays (LCD) or other forms of screen.
Examples of such screens are the EFIS and ECAM displays on modern aircraft.
The standard output devices include printers and modems. A modem links two or more computers by translating digital signals into analogue signals so that data can be transmitted via telecommunications.
Outputs may also be in the form of signals that are sent to the operating devices and are typically used to control the engines or automatic flight control system on the aircraft.
STORAGE DEVICES
Computer systems can store data internally (in memory) and externally (on storage devices). External storage devices may physically reside within the computer's main processing unit or externally to the main circuit board. These devices store data as electrical charges on a magnetically sensitive medium such as an audiotape, a disk coated with a fine layer of metallic particles, or as an imprint on a laser readable disk. The most common external storage devices are floppy and hard disks. Floppy disks can contain from several hundred thousand bytes to well over a million bytes of data, depending on the system. Hard or fixed disks cannot be removed from their disk-drive cabinets, which contain the electronics to read and write data onto the magnetic disk surfaces. Hard disks can store from several million bytes to a few hundred million bytes. CD-ROM technologies, which use the same laser techniques that are used to create audio compact disks (CDs), also provide storage capacities in the range of several gigabytes (billion bytes) of data.