Computer Architecture
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The document provides an overview of computer architecture, detailing the components of a computer system such as the CPU, memory, control unit, and ALU. It explains the functions of these components, the communication between them, and the architecture's implications on processing speed, as well as describing instruction formats and multiprocessor systems. The advantages and disadvantages of multiprocessor systems are also examined, highlighting economic benefits and complexities involved in their operation.
Computer Architecture
- 1. Introduction to Computer Science Computer Architecture Prepared By: S. K. Barnwal Assistant Professor Arka Jain University Research Scholar (NIT, JSR)
- 2. Introduction • A computer system is basically a machine that simplifies complicated tasks. It should maximize performance and reduce costs as well as power consumptions. The different components in the Computer System Architecture are Input Unit, Output Unit, Storage Unit, Arithmetic Logic Unit, Control Unit etc. • Computer architecture is a set of rules and methods that describe the functionality, organization and implementation of computer systems. ALU CU M/M I/P O/P
- 3. CPU (Central Processing Unit) • A central processing unit (CPU) is the electronic circuitry within a computer that carries out the instructions of a computer program by performing the basic arithmetic, logical, control and input/output (I/O) operations specified by the instructions. • The input data travels from input unit to ALU. Similarly, the computed data travels from ALU to output unit. The data constantly moves from storage unit to ALU and back again. This is because stored data is computed on before being stored again. The control unit controls all the other units as well as their data. Central Processing Unit (CPU) consists of the following features − • CPU is considered as the brain of the computer. • CPU performs all types of data processing operations. • It stores data, intermediate results, and instructions (program). • It controls the operation of all parts of the computer.
- 4. CPU CPU itself has following three components. • Memory or Storage Unit • Control Unit • ALU(Arithmetic Logic Unit) Memory or Storage Unit • This unit can store instructions, data, and intermediate results. This unit supplies information to other units of the computer when needed. It is also known as internal storage unit or the main memory or the primary storage or Random Access Memory (RAM). • Its size affects speed, power, and capability. Primary memory and secondary memory are two types of memories in the computer.
- 5. CPU Functions of the memory unit are − • It stores all the data and the instructions required for processing. • It stores intermediate results of processing. • It stores the final results of processing before these results are released to an output device. • All inputs and outputs are transmitted through the main memory. Control Unit • This unit controls the operations of all parts of the computer but does not carry out any actual data processing operations. Functions of this unit are − • It is responsible for controlling the transfer of data and instructions among other units of a computer. • It manages and coordinates all the units of the computer. • It obtains the instructions from the memory, interprets them, and directs the operation of the computer.
- 6. CPU • It communicates with Input/Output devices for transfer of data or results from storage. • It does not process or store data. ALU (Arithmetic Logic Unit) • This unit consists of two subsections namely, • Arithmetic Section • Logic Section • Arithmetic Section: Function of arithmetic section is to perform arithmetic operations like addition, subtraction, multiplication, and division. All complex operations are done by making repetitive use of the above operations. • Logic Section: Function of logic section is to perform logic operations such as comparing, selecting, matching, and merging of data.
- 7. Communication between Various Units of a Computer System • Input Unit: The input unit provides data to the computer system from the outside. So, basically it links the external environment with the computer. It takes data from the input devices, converts it into machine language and then loads it into the computer system. Keyboard, mouse etc. are the most commonly used input devices. • Output Unit: The output unit provides the results of computer process to the users i.e it links the computer with the external environment. Most of the output data is the form of audio or video. The different output devices are monitors, printers, speakers, headphones etc. • CPU: CPU is considered as the brain of the computer. CPU performs all types of data processing operations. It stores data, intermediate results, and instructions (program). It controls the operation of all parts of the computer.
- 8. The Instruction Format Computer perform task on the basis of instruction provided. An instruction in computer comprises of groups called fields. These fields contain different information as for computers every things is in 0 and 1 so each field has different significance on the basis of which a CPU decide what to perform. The most common fields are: • Operation field which specifies the operation to be performed like addition. • Address field that consist the location of operand, i.e., register or memory location. • Mode field which specifies how operand is to be founded. • Zero Address Instructions – A stack based computer do not use address field in instruction. (Ex; PUSH A, POP A)
- 9. The Instruction Format • One Address Instructions– This uses a implied ACCUMULATOR register for data manipulation. One operand is in accumulator and other is in register or memory location. Implied means that the CPU already know that one operand is in accumulator so there is no need to specify it. (Ex; ADD A, MUL C, ADD 55 etc) • Two Address Instructions – This is common in commercial computers. Here two address can be specified in the instructions. Unlike earlier in one address instruction the result was stored in accumulator here result cab be stored at different location rather than just accumulator, but require more number of bit to represent address. Here destination address can also contain operand. (Ex; ADD A, B; ADD R1, A) • Three Address Instructions – This has three address field to specify a register or a memory location. Program created are much short in size but number of bits per instruction increase. (Ex; ADD R1, A, B)
- 10. Instruction Set The instruction set, also called ISA (instruction set architecture), and is part of a computer that pertains to programming, which is more or less machine language. The instruction set provides commands to the processor, to tell it what it needs to do. The instruction set consists of addressing modes, instructions, native data types, registers, memory architecture, interrupt, and exception handling, and external I/O. Examples of instruction set • ADD - Add two numbers together. • COMPARE - Compare numbers. • IN - Input information from a device, e.g., keyboard. • JUMP - Jump to designated RAM address. • JUMP IF - Conditional statement that jumps to a designated RAM address. • LOAD - Load information from RAM to the CPU. • OUT - Output information to device, e.g., monitor. • STORE - Store information to RAM.
- 11. Processor Speed • Processor speed measures (in megahertz or gigahertz; MHz or GHz) the number of instructions per second the computer executes. • A computer’s processor clock speed determines how quickly the central processing unit (CPU) can retrieve and interpret instructions. This helps our computer complete more tasks by getting them done faster. • Faster clock speeds mean that we’ll see tasks ordered from our CPU completed quicker, making our experience seamless and reducing the time you wait to interface with our favorite applications and programs.
- 12. Multiprocessor Systems Most computer systems are single processor systems i.e they only have one processor. However, multiprocessor or parallel systems are increasing in importance nowadays. These systems have multiple processors working in parallel that share the computer clock, memory, bus, peripheral devices etc. There are two types of multiprocessors, one is called shared memory multiprocessor and another is distributed memory multiprocessor. In shared memory multiprocessors, all the CPUs shares the common memory but in a distributed memory multiprocessor, every CPU has its own private memory.
- 13. Multiprocessor System Advantages of Multiprocessor Systems • More reliable Systems: In a multiprocessor system, even if one processor fails, the system will not halt. This ability to continue working despite hardware failure is known as graceful degradation. For example: If there are 5 processors in a multiprocessor system and one of them fails, then also 4 processors are still working. So the system only becomes slower and does not ground to a halt. • Enhanced Throughput: If multiple processors are working in tandem, then the throughput of the system increases i.e. number of processes getting executed per unit of time increase. If there are N processors then the throughput increases by an amount N. • More Economic Systems: Multiprocessor systems are cheaper than single processor systems in the long run because they share the data storage, peripheral devices, power supplies etc. If there are multiple processes that share data, it is better to schedule them on multiprocessor systems with shared data than have different computer systems with multiple copies of the data.
- 14. Multiprocessor System Disadvantages of Multiprocessor Systems • Increased Expense: Even though multiprocessor systems are cheaper in the long run than using multiple computer systems, still they are quite expensive. It is much cheaper to buy a simple single processor system than a multiprocessor system. • Complicated Operating System Required: There are multiple processors in a multiprocessor system that share peripherals, memory etc. So, it is much more complicated to schedule processes and impart resources to processes than in single processor systems. Hence, a more complex and complicated operating system is required in multiprocessor systems. • Large Main Memory Required: All the processors in the multiprocessor system share the memory. So a much larger pool of memory is required as compared to single processor systems.