What is the part component of the computer that manages instructions including the functions of the input and output devices?

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The central processing unit (CPU) is the primary component of any digital computer system, consisting of the main memory, the control unit, and the arithmetic-logic unit. It is the physical heart of the entire computer system, to which various peripheral equipment, such as input/output devices and auxiliary storage units, are connected. The CPU in modern computers is housed on an integrated circuit chip known as a microprocessor.

A microprocessor is a small electronic device that contains the arithmetic, logic, and control circuitry required to perform the functions of a digital computer’s central processing unit. In practice, this type of integrated circuit is capable of interpreting and executing program instructions in addition to performing arithmetic operations.

The central processing unit’s control unit regulates and integrates the computer’s operations. It selects and retrieves instructions from the main memory in the correct sequence and interprets them so that the other functional elements of the system can perform their respective operations at the appropriate time. All input data are transferred via main memory to the arithmetic-logic unit for processing, which includes the four basic arithmetic functions (addition, subtraction, multiplication, and division) as well as certain logic operations such as data comparison and selection of the desired problem-solving procedure or a viable alternative based on predetermined decision criteria.

The Central Processing Unit (CPU) has the following characteristics:

• The CPU is regarded as the computer’s brain.
• The CPU is responsible for all data processing operations.
• It saves information such as data, intermediate results, and instructions (program).
• It directs the operation of all computer components.

The CPU itself is made up of the three components listed below.

1. Memory or Storage Unit
2. Control Unit
3. Arithmetic Logic Unit

Memory or Storage Unit

This unit has the capability of storing instructions, data, and intermediate results. When necessary, this unit sends data to other computer units. It is also referred to as an internal storage unit, main memory, primary storage, or Random Access Memory (RAM). Its size has an impact on its speed, power, and capability. In a computer, there are two types of memories: primary memory and secondary memory. The memory unit’s functions are as follows:

• It saves all of the data and instructions needed for processing.
• It saves intermediate processing results.
• It saves the final results of processing before they are sent to an output device.
• The main memory is where all inputs and outputs are routed.

The Control Unit

This unit manages the operations of all computer components but does not perform any actual data processing. To function properly, all CPU components must be synchronized. The control unit performs this function at a rate determined by the clock speed and is in charge of directing the operations of the other units through the use of timing signals that run throughout the CPU.

This unit’s functions are as follows:

• It is in charge of controlling the transfer of data and instructions among the various components of a computer.
• It manages and coordinates all of the computer’s units.
• It reads instructions from memory, interprets them, and directs the computer’s operation.
• It communicates with Input/Output devices to transfer data.
• It neither processes nor stores data.

Arithmetic Logic Unit

This unit is divided into two subsections, namely,

Sections of Arithmetic and Logic

Arithmetic Unit
The arithmetic unit’s function is to perform arithmetic operations such as addition, subtraction, multiplication, and division. All complex operations are carried out by repeatedly performing the aforementioned operations.

Logic Unit
The logic unit’s function is to perform logic operations on data such as comparing, selecting, matching, and merging.

The arithmetic logic unit (ALU) is responsible for the computer’s arithmetic and logical functions. The input data is held in the A and B registers, and the result of the operation is received in the accumulator. The instruction register stores the instruction that the ALU will execute.

When adding two numbers, for example, one is placed in the A register and the other in the B register. The addition is performed by the ALU, and the result is stored in the accumulator. The data to be compared is placed into the input registers if the operation is logical. The comparison result, a 1 or 0, is stored in the accumulator. The accumulator content is then placed into the cache location reserved by the program for the result, whether it is a logical or arithmetic operation.

The ALU also performs another type of operation. The result is a memory address, which is used to calculate a new memory location to begin loading instructions. The outcome is stored in the instruction pointer register.

Instruction register and pointer

The instruction pointer identifies the memory location in which the CPU will execute the next instruction. When the current instruction is completed, the CPU loads the next instruction into the instruction register from the memory location specified by the instruction pointer.

Cache

The CPU never has direct access to RAM. Modern CPUs have one or more cache layers. The CPU’s calculation speed is much faster than the RAM’s ability to feed data to the CPU.

Cache memory is faster than system RAM and, because it is located on the processor chip, it is closer to the CPU. The cache stores data and instructions to keep the CPU from having to wait for data to be retrieved from RAM. When the CPU requires data—and program instructions are considered data—the cache checks to see if the data is already in residence and returns it to the CPU.

If the requested data is not in the cache, it is retrieved from RAM and used to move more data from RAM into the cache using predictive algorithms. The cache controller analyses the requested data and attempts to predict what additional data from RAM will be required. It loads the expected data into the cache. By storing some data closer to the CPU in a faster-than-RAM cache, the CPU can stay busy and avoid wasting cycles waiting for data.

Our simple CPU has three cache levels. Levels 2 and 3 are intended to predict what data and program instructions will be required next, and to move that data from RAM to a location closer to the CPU so that it is ready when needed. These cache sizes typically range from 1 MB to 32 MB, depending on the processor’s speed and intended use.

Computer: A computer is a combination of hardware and software resources which integrate together and provides various functionalities to the user. Hardware are the physical components of a computer like the processor, memory devices, monitor, keyboard etc. while software is the set of programs or instructions that are required by the hardware resources to function properly. 
There are a few basic components that aids the working-cycle of a computer i.e. the Input- Process- Output Cycle and these are called as the functional components of a computer. It needs certain input, processes that input and produces the desired output. The input unit takes the input, the central processing unit does the processing of data and the output unit produces the output. The memory unit holds the data and instructions during the processing. 

Digital Computer: A digital computer can be defined as a programmable machine which reads the binary data passed as instructions, processes this binary data, and displays a calculated digital output. Therefore, Digital computers are those that work on the digital data. 

Details of Functional Components of a Digital Computer

• Input Unit :The input unit consists of input devices that are attached to the computer. These devices take input and convert it into binary language that the computer understands. Some of the common input devices are keyboard, mouse, joystick, scanner etc.
• Central Processing Unit (CPU) : Once the information is entered into the computer by the input device, the processor processes it. The CPU is called the brain of the computer because it is the control center of the computer. It first fetches instructions from memory and then interprets them so as to know what is to be done. If required, data is fetched from memory or input device. Thereafter CPU executes or performs the required computation and then either stores the output or displays on the output device. The CPU has three main components which are responsible for different functions – Arithmetic Logic Unit (ALU), Control Unit (CU) and Memory registers
• Arithmetic and Logic Unit (ALU) : The ALU, as its name suggests performs mathematical calculations and takes logical decisions. Arithmetic calculations include addition, subtraction, multiplication and division. Logical decisions involve comparison of two data items to see which one is larger or smaller or equal.
• Control Unit : The Control unit coordinates and controls the data flow in and out of CPU and also controls all the operations of ALU, memory registers and also input/output units. It is also responsible for carrying out all the instructions stored in the program. It decodes the fetched instruction, interprets it and sends control signals to input/output devices until the required operation is done properly by ALU and memory.
• Memory Registers : A register is a temporary unit of memory in the CPU. These are used to store the data which is directly used by the processor. Registers can be of different sizes(16 bit, 32 bit, 64 bit and so on) and each register inside the CPU has a specific function like storing data, storing an instruction, storing address of a location in memory etc. The user registers can be used by an assembly language programmer for storing operands, intermediate results etc. Accumulator (ACC) is the main register in the ALU and contains one of the operands of an operation to be performed in the ALU.
• Memory : Memory attached to the CPU is used for storage of data and instructions and is called internal memory The internal memory is divided into many storage locations, each of which can store data or instructions. Each memory location is of the same size and has an address. With the help of the address, the computer can read any memory location easily without having to search the entire memory. when a program is executed, it’s data is copied to the internal memory and is stored in the memory till the end of the execution. The internal memory is also called the Primary memory or Main memory. This memory is also called as RAM, i.e. Random Access Memory. The time of access of data is independent of its location in memory, therefore this memory is also called Random Access memory (RAM). Read this for different types of RAMs
• Output Unit : The output unit consists of output devices that are attached with the computer. It converts the binary data coming from CPU to human understandable form. The common output devices are monitor, printer, plotter etc.

Interconnection between Functional Components

A computer consists of input unit that takes input, a CPU that processes the input and an output unit that produces output. All these devices communicate with each other through a common bus. A bus is a transmission path, made of a set of conducting wires over which data or information in the form of electric signals, is passed from one component to another in a computer. The bus can be of three types – Address bus, Data bus and Control Bus. 

Following figure shows the connection of various functional components: 

The address bus carries the address location of the data or instruction. The data bus carries data from one component to another and the control bus carries the control signals. The system bus is the common communication path that carries signals to/from CPU, main memory and input/output devices. The input/output devices communicate with the system bus through the controller circuit which helps in managing various input/output devices attached to the computer.
 

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