The UGC NET Computer Science (Computer System Architecture)

 The UGC NET Computer Science (Computer System Architecture)

Introduction

In this article, you will be able to know and learn about some important terminologies, and MCQs that are frequently asked in the UGC NET Computer Science (Computer System Architecture).

Computer System Architecture

·       Computer System Architecture is the organization of the components which make up a computer system and the meaning of the operations which guide its function.

·       Computer System Architecture is a set of interconnected building blocks, each of which performs a particular function in the system.

·       Computer System Architecture is the conceptual design and fundamental operational structure of a computer system.

·       Computer System Architecture defines what is seen on the machine interface, which is targeted by programming languages and their compilers.

·       Computer System Architecture includes a CPU, a memory unit, and a GPU (Graphical Processing Unit).

In a computer system, data transfer takes place between processor registers and memory and between processor registers and the input-output systems.

General register organization

·       General register organization is the processor architecture that stores and manipulates data for computations.

·       The main components of a register organization include registers, memory, and instructions.

Register

·       A set of flip-flops forms a register.

·       A register is a small, high-speed storage area within a computer’s processor or CPU.

·       A register is the most elementary data-storing device that is implemented onto the processor chip itself.

·       Registers hold operands or instructions that the CPU would be currently processing.

·       The processor can directly access the data stored in registers.

·       Registers allow the processor to quickly access and manipulate the stored information.

·       Registers can be controlled.

Register transfer

Register transfer refers to the availability of hardware logic circuits that can perform a given micro-operation and transfer the result of the operation to the same or another register.

Register transfer micro-operations

Register transfer micro-operations transfer binary information from one register to another.

Micro-operations

·       Micro-operations are also known as micro-ops.

·       Micro-operations refer to the operations made by the CPU to fetch values (operands) stored in memory (registers) and execute instructions.

·       A Micro-operation is an elementary operation performed on the information stored in one or more registers in the CPU.

·       Some examples of Micro-operations are shift, count, clear, and load.

Arithmetic micro-operations

Arithmetic micro-operations perform arithmetic operations on numeric data stored in registers.

Logical micro-operations

Logical micro-operations perform bit manipulation operations on data stored in registers.

Shift Micro-operations

Shift Micro-operations are used for the serial transfer of data and also support in conjunction with arithmetic, logic, and several data-processing operations.

The Register transfer language

The Register transfer language is the symbolic representation of notations used to specify the sequence of micro-operations.

Memory

·       Memory is a data storage device used to store data, instructions, and computer programs.

·       Memory holds instructions and the data about the currently executing program required by the CPU.

·       Memory is typically larger and more long-term in nature.

· Memory can’t be controlled. 

The unit of transfer in memory

The unit of transfer in memory is the number of bits read out of or written into memory at a time.

Block of data

·       A block is also called a physical record.

·       A block is a sequence of bytes or bits, usually containing some whole number of records, having a maximum length; a block size.

·       A data block is the smallest data unit used by a database.

·       Data are often transferred in many large units than a word, which is referred to as blocks.

Memory transfer

·       Memory transfer means the transfer of data from memory to the external environment or the transfer of new data into the memory.

·       Operations of Memory transfer are Read, Write, and both.

Write operation

·       Write operation refers to transferring new information stored in the memory.

·       The memory transfer in the write operation is the transfer of data from the memory buffer register (MBR) to the address register (AR) with the chosen word M for the memory. (A memory word is symbolized by M).

Read operation

Read operation refers to transferring information from a memory unit to the user.

Main memory

·       Main memory holds instructions and data when a program is executing.

·       Objective of the main memory is to store data and applications that are currently in use.

·       Main memory is the primary, internal workspace in the computer.

·       RAM is the main memory of a computer.

·       The operating system controls the usage of main memory.

Associative memory

·       Associative memory is also known as content addressable memory

·       (CAM) or associative storage or associative array.

·       Two types of associative memory in computers are auto-associative and hetero-associative.

·       Associative memory is optimized for performing searches through data.

Auxiliary memory

·       Auxiliary memory holds data and programs not currently in use and provides long-term storage.

·       Auxiliary memory holds data and programs for future use.

·       Auxiliary memory is used to store inactive programs and to archive data.

·       Auxiliary memory is non-volatile.

Memory hierarchy

·       Memory hierarchy refers to arranging different kinds of storage on a computing device based on the speed of access.

·       At the top, the highest-performing storage is CPU registers which are the fastest to read and write to.

·       Memory hierarchy is register memory, cache memory, main memory, magnetic disks, and magnetic tapes.

Cache hierarchy

Cache hierarchy or multi-level caches refers to a memory architecture that uses a hierarchy of memory stores based on varying access speeds to cache data.

Bus

·       In Computer System Architecture, a Bus is a communication system that transfers data between components inside a computer or between computers. In a digital system of registers, a path must be provided to move information.

·       A bus is a high-speed internal connection.

·       A bus is made up of a collection of common lines, one for each bit of a register, that are used to transfer binary data one by one.

·       Two methods in bus transfer are Bus transfer using Multiplexer, and Bus transfer using three states bus buffer.

·       Buses are used to send control signals and data between the processors and other components.

·       Three types of buses are address bus, data bus, and control bus.

Address bus

Address bus carries memory addresses from the processor to other components such as primary storage and input/output devices.

Data bus

The data bus carries the data between the processor and other components. The data bus is bidirectional.

Control bus

·       Control bus carries control signals from the processor to other components. The control bus also carries the clock’s pulses.

·       The control bus is unidirectional.

Interconnection structure

·       Interconnection structure refers to the collection of paths connecting the various modules.

·       Five types of interconnection structures are (a) time-shared common bus (b) multiport memory (c) crossbar switch (d) multistage switching (e) Hybercube system.

Time-shared common bus

In any multiprocessor system, the time-shared common bus interconnection structures provide a common communication path by connecting all the functional units like I/O, processor, and memory units.

 Basic computer organization

·       Computer organization is concerned with the structure and behavior of a computer system as seen by the user.

·       The basic organization of a computer system is the processing unit, memory unit, and input-output devices.

·       Five basic components of computer organization are CPU, memory unit, control unit, and ALU.

 Processing unit

The processing unit controls all the functions of the computer system.

Stored program organization

·       The simplest way to organize a computer is to have one processor register and an instruction code format with two parts. The first part specifies the operation to be performed and the second specifies an address.

·       Some common examples of stored programs are RAM and ROM.

Computer instruction

· Computer instruction is an order given to a computer processor by a computer program.

·       At the lowest level, each instruction is a sequence of 0s and 1s that describes a physical operation the computer is to perform.

Instruction code

An instruction code is a group of bits instructing the computer to perform a specific operation.

Operation Code of an Instruction

·       The Operation code of an Instruction is a group of bits that define operations such as addition, subtraction, shift, and complement.

 ·       The three different types of Instruction codes are memory reference instruction, register reference instruction and input-output instruction.

·       Each Instruction code is 16-bit and consists of three parts called fields, which include the mode, the op-code, and the address.

Memory reference instruction

Memory reference instruction uses 12 bits to specify the address and 1 bit to specify the addressing mode.

Register Reference Instruction

·       Register Reference Instructions are recognized by the opcode 111 with a 0 in the leftmost bit of instruction.

·       A Register Reference Instruction specifies an operation on or a test of the AC (Accumulator) register.

Programming language

·       A programming language refers to a system of notation for writing computer programs.

·       Programming languages are text-based formal languages, but they may also be graphical.

·       Programming languages are used to write all computer programs and computer software.

·       Some common examples of programming languages are Python, Ruby, Java, JavaScript, C, C++, and C#.

Machine language

·       Machine language is also known as machine code or object code in which instructions are executed directly by the CPU.

·       Machine language is the language understood by a computer.

·       Machine language is a low-level programming language made out of binary numbers or bits that can only be read by machines.

·       All programs and programming languages eventually generate or run programs in machine language.

Assembly language

·       Assembly language is a type of low-level programming language that is intended to communicate directly with a computer’s hardware.

·       An Assembly language consists mostly of symbolic equivalents of a particular computer’s machine language.

·       An Assembly language allows a software developer to code using words and expressions that can be easier to understand and interpret.

·       Assembly languages are designed to be readable by humans.

High-level language

·       High-level language is any programming language that enables the development of a program in a much more user-friendly programming context.

·       High-level language is generally independent of the computer’s hardware architecture.

·       A High-level language has a significant abstraction from the details of computer operation.

·       A High-level language does not require addressing hardware constraints when developing a program.

·       Every program written in a high-level language must be interpreted into machine language before being executed by the computers.

·       Some common examples of High-level languages are BASIC, C/C++, and Java.

Assembler

·       An assembler is a program that takes basic computer instructions and converts them into a pattern of bits that the computer’s processor can use to perform its basic operations.

·       An assembler completes the task in two passes. (a) It produces a machine code in form of mnemonics. (b) It produces binary code in form of 0’s and 1’s.

·       Some common examples of assemblers are Java, C, and C++.

Multiprocessor system

·       A Multiprocessor system is also known as a strongly connected system.

·       A Multiprocessor system refers to a system with more than one processor or multiple processors.

·       A Multiprocessor system contains a number of CPUs linked together to enable parallel processing to take place.

·       A Multiprocessor system is used to boost a system’s execution speed.

·       Multiprocessors have the advantage of higher throughput, increased dependability, and economies of scale.

Main characteristics of Multiprocessor

Parallel computing

Parallel computing involves the simultaneous application of multiple processors.

Distributed computing

Distributed computing involves the usage of a network of processors. Each processor in this network can be considered a computer in its own right and have the capability to solve problems. These processors are heterogeneous, and generally, one task is allocated to a single processor.

Supercomputing

·       Supercomputing involves the usage of the fastest machines to resolve big and computationally complex problems.

·       Supercomputing machines were vector computers, but at present, vector or parallel computing is accepted by most people.

Vector computing

Vector computing involves the usage of vector processors wherein operations such as “multiplication” are divided into many steps and is then applied to a stream of operands (“vectors”).

Pipelining

·       Pipelining is a process of arrangement of hardware elements of the CPU such that its overall performance is increased.

·       Pipelining is a method wherein a specific task is divided into several subtasks that must be performed in a sequence.

·       Pipelining is a technique where multiple instructions are overlapped during execution. Simultaneous execution of more than one instruction takes place in a pipelined processor.

·       Pipelining process happens in a continuous, orderly, and overlapped manner.

·       Pipelining allows storing, prioritizing, managing, and executing tasks and instructions in an orderly process.

·       Pipelining in 8086 processor, fetching the next instruction while executing the current instruction is called pipelining.

Pipeline stages are

1.  Instruction fetch

2.  Instruction decode

3. Instruction Execute

4. Memory Access

5. Write back

Instruction fetch

·       In case of instruction fetch - the CPU reads instructions from the address in the memory whose value is present in the program counter.

Memory access

·       In the case of memory access memory operands are read and written from the memory present in the instruction.

·       Efficiency = S/S_max = Given speed up/ Max speed up

·       Throughput = No. of instructions / Total time to complete the instruction

Arithmetic pipeline

·       Arithmetic pipeline separates a given arithmetic problem into sub-problems that can be executed in different pipeline segments.

·       An Arithmetic pipeline is used for multiplication, floating-point operations, and other calculations.

Control unit (CU) design

·       A CU is circuitry within a computer’s processor that directs operations.

·       CU instructs the memory, logic unit, and both output and input devices of the computer on how to respond to the program's instructions.

·       A control memory is a part of the CU. Any computer that involves micro-programmed control consists of two memories. They are the main memory and the control memory. Programs are usually stored in the main memory by the users.

·       CU is used by CPUs and GPUs.

Interprocessor Communication (IPC)

·       IPC is the mechanism provided by the OS that allows processes to communicate with each other.

·       IPC allows you to move data between loosely coupled processors using the multi-processor interconnect facility (MPIF) and channel-to-channel (CTC) communication links.

·       IPC is used for programs to communicate data to each other and to synchronize their activities.

·       Some common methods of IPC are semaphores, shared memory, and internal message queues.

·       Some common examples of IPC are POSIX uses the shared memory technique, Windows XP uses the message passing technique, and Mac uses the message passing technique.

Interprocessor arbitration

Interprocessor arbitration refers to the mechanism to solve the dispute in the system bus such that only one of the mentioned components can access it.

Interprocess synchronization

Interprocess synchronization communication refers to the exchange of data between different processes.

Synchronization

·       Synchronization refers to the special case where the data used to communicate between processors is control information.

·       Synchronization is an essential part of interprocess communication.

Stack

·       The Stack is a collection of memory locations containing a register that stores the top-of-element address in digital computers.

·       Stack is a data storage structure in which the most recent thing deposited is the most recent item retrieved.

·       Stack is based on the LIFO concept.

·       A Stack is a memory unit with an address register. This register influences the address for the stack, which is known as Stack Pointer (SP). There are two types of stacks (a) the register Stack and (b) the memory stack.

·       The two operations of a Stack are the insertion and deletion of items.

·       Nothing is pushed or popped in a computer stack.

·       The five basic operations of a Stack are (a) push (b) pop (c) is Empty (d) isFull (e) top. Push Stack is inserting an item into a Stack. Pop Stack deletes an item from the Stack. Peek or top displays the contents of the Stack. The “top” element of the Stack is the element that was last pushed and will be the first to be popped. The “bottom” element of the Stack is the element that, when removed, will leave the Stack empty.

·       Some common examples of a Stack are a pile of books, a Stack of dinner plates, and a box of Pringles potato chips.

Instruction formats

·       Instruction formats refer to a sequence of bits in a machine instruction that defines the layout of the instruction.

·       The instruction format is a pattern of bits that the control unit of the CPU can decode.

·       Instruction in computers comprises groups called fields.

Vector processing

·       Vector processing is the process of using vectors to store a large number of variables for high-intensity data processing.

·       In Vector processing, the program size is small as it requires less number of instructions.

·       A Vector processor acts on several pieces of data with a single instruction.

·       A Vector processor can improve performance on certain workloads and numerical simulation.

·       Some common examples of vector processing are weather forecasting, human genome mapping, and GIS data.