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Computer Organization & Architecture

UNIT - 1

Functional blocks of a computer, Data representation

Q1) What is computer architecture explain?

A1)

A computer system is a machine that simplifies complicated tasks. It should maximize performance and reduce costs as well as power consumption. The different components in the Computer System Architecture are Input Unit, Output Unit, Storage Unit, Arithmetic Logic Unit, Control Unit, etc.

A diagram that shows the flow of data between these units is as follows −

Computer System Architecture

The input data travels from the input unit to ALU. Similarly, the computed data travels from ALU to the output unit. The data constantly moves from the storage unit to ALU and back again. This is because stored data is computed before being stored again. The control unit controls all the other units as well as their data.

Details about all the computer units are −

Input Unit

The input unit provides data to the computer system from the outside. So, 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 the computer process to the users i.e it links the computer with the external environment. Most of the output data is in the form of audio or video. The different output devices are monitors, printers, speakers, headphones, etc.

Storage Unit

The storage unit contains many computer components that are used to store data. It is traditionally divided into primary storage and secondary storage. Primary storage is also known as the main memory and is the memory directly accessible by the CPU. Secondary or external storage is not directly accessible by the CPU. The data from secondary storage needs to be brought into the primary storage before the CPU can use it. Secondary storage contains a large amount of data permanently.

Arithmetic Logic Unit

All the calculations related to the computer system are performed by the arithmetic logic unit. It can perform operations like addition, subtraction, multiplication, division, etc. The control unit transfers data from the storage unit to the arithmetic logic unit when calculations need to be performed. The arithmetic logic unit and the control unit together form the central processing unit.

Control Unit

This unit controls all the other units of the computer system and so is known as its central nervous system. It transfers data throughout the computer as required including from the storage unit to the central processing unit and vice versa. The control unit also dictates how the memory, input-output devices, arithmetic logic unit, etc. should behave.

Q2) Explain CPU(Central processing unit)

A2)

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.

CPU

CPU itself has the following three components.

Memory or Storage Unit

Control Unit

ALU(Arithmetic Logic Unit)

Computer Architectures

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 the 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. 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.

It communicates with input/output devices for the 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

The function of the 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

The function of the logic section is to perform logic operations such as comparing, selecting, matching, and merging data.

Q3) Explain memory and its types in detail

A3)

A memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage space in the computer, where data is to be processed and instructions required for processing are stored. The memory is divided into a large number of small parts called cells. Each location or cell has a unique address, which varies from zero to memory size minus one. For example, if the computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory locations. The address of these locations varies from 0 to 65535.

Memory is primarily of three types −

Cache Memory

Primary Memory/Main Memory

Secondary Memory

Cache Memory

Cache memory is a very high-speed semiconductor memory that can speed up the CPU. It acts as a buffer between the CPU and the main memory. It is used to hold those parts of data and program which are most frequently used by the CPU. The parts of data and programs are transferred from the disk to cache memory by the operating system, from where the CPU can access them.

Cache Memory

Advantages

The advantages of cache memory are as follows −

Cache memory is faster than main memory.

It consumes less access time as compared to main memory.

It stores the program that can be executed within a short period.

It stores data for temporary use.

Disadvantages

The disadvantages of cache memory are as follows −

Cache memory has limited capacity.

It is very expensive.

Primary Memory (Main Memory)

Primary memory holds only those data and instructions on which the computer is currently working. It has a limited capacity and data is lost when power is switched off. It is generally made up of semiconductor devices. These memories are not as fast as registers. The data and instruction required to be processed resides in the main memory. It is divided into two subcategories RAM and ROM.

Primary Memory

Characteristics of Main Memory

These are semiconductor memories.

It is known as the main memory.

Usually volatile memory.

Data is lost in case power is switched off.

It is the working memory of the computer.

Faster than secondary memories.

A computer cannot run without the primary memory.

Secondary Memory

This type of memory is also known as external memory or non-volatile. It is slower than the main memory. These are used for storing data/information permanently. CPU directly does not access these memories, instead, they are accessed via input-output routines. The contents of secondary memories are first transferred to the main memory, and then the CPU can access it. For example, disk, CD-ROM, DVD, etc.

Secondar Memory

Characteristics of Secondary Memory

These are magnetic and optical memories.

It is known as backup memory.

It is a non-volatile memory.

Data is permanently stored even if power is switched off.

It is used for the storage of data on a computer.

The computer may run without secondary memory.

Slower than primary memories.

Q4) Explain bus topology

A4)

Bus Topology

Computer Network Topologies

The bus topology is designed in such a way that all the stations are connected through a single cable known as a backbone cable.

Each node is either connected to the backbone cable by drop cable or directly connected to the backbone cable.

When a node wants to send a message over the network, it puts a message over the network. All the stations available in the network will receive the message whether it has been addressed or not.

The bus topology is mainly used in 802.3 (ethernet) and 802.4 standard networks.

The configuration of a bus topology is quite simpler as compared to other topologies.

The backbone cable is considered as a "single lane" through which the message is broadcast to all the stations.

The most common access method of the bus topologies is CSMA (Carrier Sense Multiple Access).

CSMA: It is a media access control used to control the data flow so that data integrity is maintained, i.e., the packets do not get lost. There are two alternative ways of handling the problems that occur when two nodes send the messages simultaneously.

CSMA CD: CSMA CD (Collision detection) is an access method used to detect the collision. Once the collision is detected, the sender will stop transmitting the data. Therefore, it works on "recovery after the collision".

CSMA CA: CSMA CA (Collision Avoidance) is an access method used to avoid the collision by checking whether the transmission media is busy or not. If busy, then the sender waits until the media becomes idle. This technique effectively reduces the possibility of collision. It does not work on "recovery after the collision".

Advantages of Bus topology:

Low-cost cable: In a bus topology, nodes are directly connected to the cable without passing through a hub. Therefore, the initial cost of installation is low.

Moderate data speeds: Coaxial or twisted pair cables are mainly used in bus-based networks that support up to 10 Mbps.

Familiar technology: Bus topology is a familiar technology as the installation and troubleshooting techniques are well known, and hardware components are easily available.

Limited failure: A failure in one node will not have any effect on other nodes.

Disadvantages of Bus topology:

Extensive cabling: A bus topology is quite simpler, but still it requires a lot of cabling.

Difficult troubleshooting: It requires specialized test equipment to determine the cable faults. If any fault occurs in the cable, then it would disrupt the communication for all the nodes.

Signal interference: If two nodes send the messages simultaneously, then the signals of both the nodes collide with each other.

Reconfiguration difficult: Adding new devices to the network would slow down the network.

Attenuation: Attenuation is a loss of signal that leads to communication issues. Repeaters are used to regenerate the signal.

Q5) Explain hard disk drive

A5)

Hard Disk Drive (HDD)

Hard Disk Drive Storage Device - GCSE

What is a hard disk drive?

Hard disk drives are non-volatile magnetic storage devices capable of remembering vast amounts of data.

An electromagnet in the read/write head changes the disk’s surface with either a positive or negative charge, this is how binary 1 or 0 is represented.

The read/write head is then capable of detecting the magnetic charges left on the disk’s surface, this is how data is read.

The disk surface is divided into concentric circles (tracks) and sectors (wedges). Dividing the surface in this way provides physical addresses to remember where data is saved.

A circuit board carefully co-ordinates the rotating disk and swinging actuator arm to allow the read/write head to access any location very quickly.

Typical HDD capacities are measured in Terabytes (TB).

They can be installed inside a computer or purchased in a portable (external) format.

Typical applications for hard disk drives

Desktop computers

Laptop computers

TV and satellite recorders

Servers and mainframes

Portable (external) drives are sometimes used to backup home computers or transfer large files

Benefits of hard disk drives

Capable of holding vast amounts of data at affordable prices

Fast read and write speeds

Reliable technology

Relatively small in size

Drawbacks of hard disk drives

Due to the nature of its moving parts, they will eventually wear and break

Although very fast, waiting for the moving parts means it will never perform as fast as solid-state drives

More fragile and less robust than a solid-state drive

Higher power consumption than an SSD

Some noise is created by the moving parts

Q6) Explain RAM in detail

A6)

Random Access Memory (RAM)

RAM - Storage Device, GCSE Computer Science

What is RAM?

RAM is a computer’s primary memory. It is a very fast solid-state storage medium that is directly accessible by the CPU.

Any open programs or files on a computer are temporarily stored in RAM whilst being used.

Being volatile, any data stored in RAM will be lost when power is removed. This makes RAM unsuitable for the long-term permanent storage of data – that is the role of an HDD or SSD instead.

Data is copied from secondary storage (HDD, SSD) to RAM as and when it is needed. This is because using an HDD as the primary memory would cause a computer to perform much slower (an HDD or SSD is not directly accessible to the CPU, and isn’t as fast as RAM).

RAM is a relatively expensive storage device and typical capacities are measured in Gigabytes (GB).

Computers operating with a capacity of RAM above the recommended minimum will benefit from better performance and multitasking.

There are two types of RAM (SRAM and DRAM), each with its advantages and disadvantages.

Typical applications of RAM

The fast and directly accessible temporary (working) memory needed by a computer

Benefits of RAM

Directly accessible to the CPU, making processing data faster

Fast solid-state storage, making processing data faster

Drawbacks of RAM

Relatively expensive memory

Volatile – any data stored in RAM is lost when power is removed

Static RAM (SRAM)

Data on SRAM does not require refreshing.

However, the technology is bulkier meaningless memory per chip.

More expensive than DRAM

Much faster than DRAM

Consumes less power

Commonly used in the cache memory

Dynamic RAM (DRAM)

The most common type of RAM in use.

The data needs to be continually refreshed otherwise it fades away.

Continually refreshing the data takes time and reduces performance speeds.

Cheaper than SRAM

Commonly used in main memory

Q7) What is a programming language?

A7)

We assume you are well aware of English Language, which is a well-known Human Interface Language. English has a predefined grammar, which needs to be followed to write English statements correctly. Likewise, most of the Human Interface Languages (Hindi, English, Spanish, French, etc.) are made of several elements like verbs, nouns, adjectives, adverbs, propositions, and conjunctions, etc.

Similar to Human Interface Languages, Computer Programming Languages are also made of several elements. We will take you through the basics of those elements and make you comfortable to use them in various programming languages. These basic elements include −

Programming Environment

Basic Syntax

Data Types

Variables

Keywords

Basic Operators

Decision Making

Loops

Numbers

Characters

Arrays

Strings

Functions

File I/O

We will explain all these elements in subsequent chapters with examples using different programming languages. First, we will try to understand the meaning of all these terms in general, and then, we will see how these terms can be used in different programming languages.

This tutorial has been designed to give you an idea about the following most popular programming languages −

C Programming

Java Programming

Python Programming

A major part of the tutorial has been explained by taking C as a programming language and then we have shown how similar concepts work in Java and Python. So after completion of this tutorial, you will be quite familiar with these popular programming languages.

Q8) What are the types of programming language?

A8)

A programming language defines a set of instructions that are compiled together to perform a specific task by the CPU (Central Processing Unit). The programming language mainly refers to high-level languages such as C, C++, Pascal, Ada, COBOL, etc.

Each programming language contains a unique set of keywords and syntax, which are used to create a set of instructions. Thousands of programming languages have been developed till now, but each language has its specific purpose. These languages vary in the level of abstraction they provide from the hardware. Some programming languages provide less or no abstraction while some provide higher abstraction. Based on the levels of abstraction, they can be classified into two categories:

Low-level language

High-level language

The image which is given below describes the abstraction level from the hardware. As we can observe from the below image that the machine language provides no abstraction, assembly language provides less abstraction whereas high-level language provides a higher level of abstraction.

Classification of Programming Language

Low-level language

The low-level language is a programming language that provides no abstraction from the hardware, and it is represented in 0 or 1 forms, which are the machine instructions. The languages that come under this category are the Machine level language and Assembly language.

Machine-level language

The machine-level language is a language that consists of a set of instructions that are in the binary form 0 or 1. As we know that computers can understand only machine instructions, which are in binary digits, i.e., 0 and 1, so the instructions given to the computer can be only in binary codes. Creating a program in a machine-level language is a very difficult task as it is not easy for the programmers to write the program in machine instructions. It is error-prone as it is not easy to understand, and its maintenance is also very high. A machine-level language is not portable as each computer has its machine instructions, so if we write a program on one computer will no longer be valid on another computer.

The different processor architectures use different machine codes, for example, a PowerPC processor contains RISC architecture, which requires different code than an intel x86 processor, which has a CISC architecture.

Assembly Language

The assembly language contains some human-readable commands such as mov, add, sub, etc. The problems which we were facing in machine-level language are reduced to some extent by using an extended form of machine-level language known as assembly language. Since assembly language instructions are written in English words like mov, add, sub, so it is easier to write and understand.

As we know that computers can only understand machine-level instructions, so we require a translator that converts the assembly code into machine code. The translator used for translating the code is known as an assembler.

The assembly language code is not portable because the data is stored in computer registers, and the computer has to know the different sets of registers.

The assembly code is not faster than machine code because the assembly language comes above the machine language in the hierarchy, so it means that assembly language has some abstraction from the hardware while machine language has zero abstraction.

Q9) Differences between Machine-Level language and Assembly language

A9)

The following are the differences between machine-level language and assembly language:

Machine-level language	Assembly language
The machine-level language comes at the lowest level in the hierarchy, so it has zero abstraction level from the hardware.	The assembly language comes above the machine language means that it has less abstraction level from the hardware.
It cannot be easily understood by humans.	It is easy to read, write, and maintain.
The machine-level language is written in binary digits, i.e., 0 and 1.	The assembly language is written in simple English language, so it is easily understandable by the users.
It does not require any translator as the machine code is directly executed by the computer.	In assembly language, the assembler is used to convert the assembly code into machine code.
It is a first-generation programming language.	It is a second-generation programming language.

Q10) Explain compiler and interpreter in detail

A10)

What is Compiler?

A compiler is a computer program that transforms code written in a high-level programming language into machine code. It is a program that translates the human-readable code to a language a computer processor understands (binary 1 and 0 bits). The computer processes the machine code to perform the corresponding tasks.

A compiler should comply with the syntax rule of that programming language in which it is written. However, the compiler is only a program and cannot fix errors found in that program. So, if you make a mistake, you need to make changes in the syntax of your program. Otherwise, it will not compile.

What is an Interpreter?

An interpreter is a computer program, which covers each high-level program statement into the machine code. This includes source code, pre-compiled code, and scripts. Both compiler and interpreters do the same job which is converting higher-level programming language to machine code. However, a compiler will convert the code into machine code (create an exe) before the program run. Interpreters convert code into machine code when the program is run.

KEY DIFFERENCE

The compiler transforms code written in a high-level programming language into the machine code, at once, before the program runs, whereas the Interpreter covers each high-level program statement, one by one, into the machine code, during the program run.

Compiled code runs faster while interpreted code runs slower.

Compiler displays all errors after compilation; on the other hand, the Interpreter displays errors of each line one by one.

The compiler is based on the translation linking-loading model, whereas the Interpreter is based on Interpretation Method.

The compiler takes an entire program whereas the Interpreter takes a single line of code.

Difference between Compiler and Interpreter

Basis of difference	Compiler	Interpreter
Programming Steps	Create the program. Compile will parse or analyses all of the language statements for their correctness. If incorrect, throws an error If no error, the compiler will convert the source code to machine code. It links different code files into a runnable program(known as exe) Run the Program	Create the Program No linking of files or machine code generation Source statements executed line by line DURING Execution
Advantage	The program code is already translated into machine code. Thus, it code execution time is less.	Interpreters are easier to use, especially for beginners.
Disadvantage	You can't change the program without going back to the source code.	Interpreted programs can run on computers that have the corresponding interpreter.
Machine code	Store machine language as machine code on the disk	Not saving machine code at all.
Running time	Compiled code run faster	Interpreted code run slower
Model	It is based on the language translation linking-loading model.	It is based on Interpretation Method.
Program generation	Generates output program (in the form of exe) which can be run independently from the original program.	Do not generate an output program. So they evaluate the source program every time during execution.
Execution	Program execution is separate from the compilation. It is performed only after the entire output program is compiled.	Program Execution is a part of the Interpretation process, so it is performed line by line.
Memory requirement	Target programs execute independently and do not require the compiler in the memory.	The interpreter exists in the memory during interpretation.
Best suited for	Bounded to the specific target machine and cannot be ported. C and C++ are a most popular a programming language which uses compilation model.	For web environments, where load times are important. Due to all the exhaustive analysis is done, compiles take a relatively larger time to compile even small code that may not be run multiple times. In such cases, interpreters are better.
Code Optimization	The compiler sees the entire code upfront. Hence, they perform lots of optimizations that make code run faster	Interpreters see code line by line, and thus optimizations are not as robust as compilers
Dynamic Typing	Difficult to implement as compilers cannot predict what happens at turn time.	Interpreted languages support Dynamic Typing
Usage	It is best suited for the Production Environment	It is best suited for the program and development environment.
Error execution	Compiler displays all errors and warning at the compilation time. Therefore, you can't run the program without fixing errors	The interpreter reads a single statement and shows the error if any. You must correct the error to interpret the next line.
Input	It takes an entire program	It takes a single line of code.
Output	Compliers generate intermediate machine code.	The interpreter never generates any intermediate machine code.
Errors	Display all errors after, compilation, all at the same time.	Displays all errors of each line one by one.
Pertaining Programming languages	C, C++, C#, Scala, Java all use complier.	PHP, Perl, Ruby uses an interpreter.

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