It is an electronic machine which takes data as input, processes it and gives information as output. A computer that represents discrete(digital) information by numerical (binary) digits is called a digital computer. Generally it uses binary number system and thus it can understand only 0 and 1.
Basic Units of Digital Computer :
- Input: The user gives a set of input data.
- Processing: The input data is processed by a well-defined and finite sequence of steps.
- Output: Some data available from the processing step are output to the user.
The basic components of a digital computer :
In order that a digital computer can solve problems, it should be equipped with the following components:
These are the devices using which the user provides input instances. In a programmable computer, input devices are also used to input programs. Examples: keyboard, mouse.
These devices notify the user about the outputs of a computation. Example: screen, printer.
The central processing unit (CPU) is the brain of the computing device and performs the basic processing steps. A CPU typically consists of:
- An arithmetic and logical unit (ALU): This provides the basic operational units of the CPU. It is made up of units (like adders, multipliers) that perform arithmetic operations on integers and real numbers, and of units that perform logical operations (logical and bitwise AND, OR etc.).
- A control unit: This unit is responsible for controlling flow of data and instructions.
- General purpose registers: A CPU usually consists of a finite number of memory cells that work as scratch locations for storing intermediate results and values.
The amount of memory (registers) resident in the CPU is typically very small and is inadequate to accommodate programs and data even of small sizes. Out-of-the-processor memory provides the desired storage space. External memory is classified into two categories:
- Main (or primary) memory : This is a high-speed memory that stays close to the CPU. Programs are first loaded in the main memory and then executed. Usually main memory is volatile, i.e., its contents are lost after power-down.
- Secondary memory : This is relatively inexpensive, bigger and low-speed memory. It is normally meant for off-line storage, i.e., storage of programs and data for future processing. One requires secondary storage to be permanent, i.e., its contents should last even after shut-down. Examples of secondary storage include floppy disks, hard disks and CDROM disks.