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IIT (BHU) CSE

Administrative Details

• Lectures, Tutorials and Lab
• Assignments – Lab, Theory
• Mid-Sem and End-Sem Exams
• Programs can be run online or in desktop, smartphones
• Online – Use GNU compiler – For example look at - https://www.onlinegdb.com/online_c_compiler
• Desktop – Install gcc compiler
• Smartphone Apps – Coding C

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Some History

• Computer technology made immense progress in last 70 years - Cost of a computer in 1985 was 1 million dollars!!!
• In 1960’s computers were stored in multiple rooms with operators overseeing their support – Used for business data processing and large-scale scientific computing
• Microprocessors came in 1970’s
• Desktop based microprocessors in 1980’s
• Emergence of Internet and World Wide Web in 1990’s
• Cellphones/smartphones (embedded computer) from 2000’s

Computer Architecture

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• Input Devices – Keyboard, Mouse
• Output Devices – Monitor, Printer
• Central Processing Unit (CPU)
• Memory – Main, Secondary

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CPU

Input Devices

Output Devices

Memory

Central Processing Unit (CPU)

• Brains of the Computer - E.g., Intel i7
• Decisions are made, computations are performed
• Contains three components
• Arithmetic Logic Unit (ALU) – Arithmetic and logical operations are performed (in binary system)
• Control Unit (CU) – Decodes and executes the instructions
• Register Set – Store pointers, counters, return address and other temporary data

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Memory Unit

• Stores program and data processed by computer
• Types – Main, Secondary, Cache
• Main memory – Random Access Memory (RAM)/Read Only Memory (ROM) - Temporary/Permanent – Fast access
• Secondary memory – Hard disk, USB pen, DVD – Permanent – Slower access
• Cache memory (Not to be confused with browser cache) – Temporary – Very fast access – Expensive
• Note temporary/volatile means data is available only till the power is on.

Operating System

• The software which runs the computer hardware

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Computer hardware

Operating system

Application programs

User

More About Operating Systems (OS)

• Hides the hardware architecture and instruction set
• Provides with standard instructions to work with irrespective of the hardware
• Acts as a resource manager – allocation and management of resources to programs
• Core of the OS is called kernel
• On top of this is a command line interpreter (CLI) also called shell
• Some application programs like text editor also come together with OS

More About OS

• Note application programs can directly access kernel services through system calls
• Common system calls – read, write, open, close, wait, exec, fork, kill
• read, write, open, close: are for files – wait: process waits for other process to complete – exec: execution of process – fork: creates a copy of itself – kill: sends termination signal to a process
• Also provides security – kernel mode/user mode
• Control over system performance

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Examples of OS

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• Some examples – UNIX/Linux, Windows –
• We also have other types like embedded OS and real-time OS
• UNIX is a powerful multitasking, multiuser operating system – 90% of world’s fastest supercomputers
• Closely associated with C language
• Linux is open source (GNU), UNIX like
• Android has Linux kernel !!

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Operating System Functions

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• Process management

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• Memory management

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• File system management

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• Device management

Process Management

• Program in execution is called process
• Each process has an address space (a list of memory locations) used to store executable program, its data and stack
• Scheduling of process – allocation of the processor
• Deadlock avoidance – deadlocks are situations when two or more processes get into stalemate situation
• OS also provides mechanism for inter-process communication

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Memory Management

• Deals with the main memory which has to be shared between OS and application programs
• Keeps programs from the programs in interfering with one another
• Management of programs address space (recall what is present in an address space?)
• Concept of virtual memory – OS keeps part of the address space in main memory and part in secondary memory – Shuttles it back and forth as needed
• Can you guess the need for virtual memory?

File system management

• Files systems are abstract organized collection of files
• Provides system calls to create, read, write, close, open, remove files
• Concept of directories where files are grouped together – system calls to manage these
• Concept of pipes related to both process and file management
• pipe is a pseudofile that connects two processes - one can send data to another by writing into this pseudofile

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I/O Device Management

• Computer receives information through input and ouput devices
• Processes access devices these using system calls
• Some part of it is device independent and others device dependent called device drivers
• Device driver controls/operates a particular device like keyboard or monitor – It’s’ a software interface to OS and application programs to use the device without knowing details about hardware
• Devices are efficiently shared among requiring them
• In UNIX I/O devices are also viewed as files!!

High-Level Programming Language

• Provides strong abstraction from the details of the computer
• Easier to use, or may automate or hide significant areas of computing systems (e.g. memory management)
• Makes the process of developing a program simpler and more understandable relative to a lower-level language
• Structured – code can be divided into smaller units or blocks
• Unstructured – single continuous or unbroken block

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Assembly Code

• Assembly Language – Mnemonics and memory addresses
• How it looks like?

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LD Acc, #12836 ;

ADD [37846] ;

STO Acc, 45632 ;

:loop ;

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Machine Code

Instructions are sequences of binary numbers

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0010011010011001

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1101010011100101

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1100010101001010

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0100101101010010

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Compiler and Interpreter

• Compiler: Translates source code from a high-level programming language to a lower level language (e.g., assembly language, object code, or machine code)

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• Interpreter:
• It’s a computer program that directly executes
• Performs, instructions written in a programming or scripting language without previously compiling into a machine language program

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Source file Hello.c

Compiler

Executable file:

Hello.exe

Integrated Development Environment (IDE)

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• IDE - Software application that provides comprehensive facilities to computer programmers for software development.

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• IDE typically consists of a source code editor, build automation tools (compiler) and a debugger.

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• For C language : Code::Blocks,Visual Studio

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Screenshot of an IDE

Some References for the course

• For C Language:
• Programming in ANSI C – Balagurusamy
• Let Us C – Kanetkar
• C Programming Language – Kernighan and Ritchie,
• C in Hindi – Kuldeep Chand
• For basics to be covered this week:
• Online resources like geeksforgeeks, tutorialspoint and several youtube channels