Operating Systems - Introduction

- May 02, 2018

Introduction

Operating system placement

An operating system (OS) is a software that manages hardware and software resources and provide common services for computer programs. Operating systems performs all the basic tasks of the computer like process management, memory management, file management, handling input and output and controlling peripheral devices such as disk drives and printers. Before go into further details, let's look into history of operating systems.

History

The First Generation (1945–55) Vacuum Tubes and Plugboards

The electronic computers first introduced in 1940s were run without any operating systems. They were designed, built, programmed, operated and maintained by a single group of people. They were programmed in absolute machine language, the basic functions of the machine were controlled using mechanical switches or jumper wires on plug boards. The programs on them were debugged using toggle switches and panel lights. ENIAC, in full Electronic Numerical Integrator and Computer, the first programmable general-purpose electronic digital computer was programmed using 1200 ten way switches.

Programmers Betty Jean Jennings (left) and Fran Bilas (right) operate ENIAC's main control panel at the Moore School of Electrical Engineering.

The Second Generation (1955–65) Transistors and Batch Systems

During this era instead of using plugboards, punched cards were used to program the computers. To run a program, a programmer would first write the program on paper, then punch it on cards. He would then insert those cards into the computer and wait until output was ready. When the output was ready, the operator would get output from the printer and carry it over to the output room, so the programmer can collect it later. Much computer time was wasted while operators were walking around the machine room. The solution for this was batch system. In the input room, full set of jobs were recorded onto a magnetic tape using an inexpensive computer. A much expensive machine was used for the real computing which was good at numerical calculations. Output was recorded in the second magnetic tape. When the output was ready, it was brought to the printing room for printing offline.

An early batch system

The Third Generation (1965–1980) ICs and Multiprogramming

Developing and maintaining two completely different product lines was an expensive task. IBM attempted to solve this problem by introducing System/360. The 360 was a series of software compatible machines differed only in price and performance. Since all the machines had the same architecture and instruction set, programs written for one machine could run on all the others. The 360 was designed to handle both scientific (i.e., numerical) and commercial computing. For 360 systems, IBM wrote extraordinary complex operating system called OS/360. It consisted of millions of lines of assembly language written by thousands of programmers and contained thousands of bugs. Every release fixed some bugs introducing new ones.

OS/360 and similar third-generation operating systems introduced a new way of performing multiple jobs at the same time called multiprogramming. Before this, it is needed CPU to sit idle and wait for I/O to finish. The solution that evolved was to partition memory into several pieces, with a different job in each partition. While one job was waiting for I/O to complete, another job could be using the CPU. If enough jobs could be held in main memory at once, the CPU could be kept busy nearly 100 percent of the time. Whenever a running job finished, the operating system could load a new job from the disk into the now-empty partition and run it. This technique is called spooling (from Simultaneous Peripheral Operation On Line) and was also used for output.

The 360 was the first major computer line to use Integrated Circuits (IC). The quick response time of these machines paved way for timesharing, a variant of multiprogramming. Timesharing allows a large number of users to interact concurrently with a single computer, lowering cost of providing computing power. The first serious timesharing system, CTSS (Compatible Time-Sharing System), was developed at M.I.T. on a specially modified 7094. The concept was to switch between each user quickly by keeping the state of the user and their programs in the machine. Switch between users would take up computer cycles, but the improvement in speed and increase in the size of core memory decreased the overhead of timesharing.

After the success of CTSS, MIT, Bell Labs, and General Electric decided to develop a machine that would support hundreds of simultaneous timesharing users. It was called MUL-TICS (MULTiplexed Information and Computing Service), influential early time-sharing operating system, based around the concept of a single-level memory. According to single-level storage, pages of memory may be in primary storage (RAM) or in secondary storage (disk); however, the current actual physical location of a page is unimportant to a process. It is usually called virtual memory. All the modern operating systems were heavily influenced by Multics. Multics featured several innovations but also presented severe problems. Because of this, Ken Thompson, Dennis Ritchie, Douglas McIlroy, and Joe Ossanna, who were the researchers at Bell Labs decided to reimplement Multics in a smaller scale. Later it was named as Unix.

Unix

Evolution of Unix and Unix-like systems

Unix is a portable, multitasking, multi-user operating system first developed in the 1960s, and has been under constant development ever since. Unix is a suite of programs that make the computer work. There are many different versions of Unix, the most popular varieties are, Sun Solaris, GNU/Linux, and MacOS X. Unix has Command line interface (CLI) as well as a Graphical user interface (GUI). Basically, Unix operating system is made up of three part.

The kernel - Allocates time and memory to programs. Handles file store and communication in response to system calls.
Shell - Executes commands typed by the user. Act as interface between user and the kernel. Commands are themselves small programs.
Programs

Unix systems are characterized by various concepts.

Directory - Directories hold files and other directories
Subdirectory - Directory inside other directory
Root directory - Top of the directory hierarchy on any Unix system
Current or Present working directory - Default directory for unix commands
Home directory - Directory for all user stuff
/home/course/csXXX/username
Path or Pathname - Gives address of location of file or directory
homeworks/hw1/prog1.cpp
Full or Absolute path - A path name starts at root directory. Begins with slash (/) character
/usr/bin/man
Relative path name - Path that starts form current directory
homeworks/test1
Command argument - Things that type at the prompt after the command name
ls -l homework
Command flag - Things that typed at the prompt as part of a command
ls -l
Text file / Binary file - A file that mainly contains letters, digits and punctuation symbols
Source code - A file that contains program code in C++ or some other programming language
Executable - A program that is ready to run
Compiling and Linking - Turning source code into an executable that can be run on the computer
Debugger - A program that allows to examine what an executable is doing while it's running
Background programs - Programs that do more stuff in background
Redirecting input into a program - Redirects input from a file into a program
command < File
Redirecting output from a program - You can capture output from a program and send it into a file
command > file
command >> file
Piping output from one program into another - You can capture output of a program and send it directly as input to another program
command1 | command2
Command history - When you execute a command, it is kept in history of login session. Use up and down arrows to access history

Everything in Unix is either a file or a process. Process is an executable program identified by a unique PID (Process identifier). A file is a collection of data, created by a user or a program. The terminal is a program that we can use to execute commands. Commands in Unix themselves are small programs. Following is a summary of the list of commands available in Unix. These commands also work in different varieties of Unix.

Command	Meaning	Examples
ls	list files and directories	ls ls ~/.. ls ~
ls -a	list all files and directories	ls -a
mkdir	make directory	mkdir mystuff
cd directory	change to named directory	cd mystuff
cd	change to home directory	cd
cd ~	change to home directory	cd ~
cd ..	change to parent directory	cd ..
pwd	display the path of current directrory	pwd
cp file1 file2	copy file1 and call it file2	cp myfile.txt myfilecopy.txt cp myfile.txt ../
mv file1 file2	move or rename file1 to file2	mv myfile.txt renamed.txt mv myfile.txt ../
rm file	remove a file	rm myfile.txt
rmdir directory	remove a directory	rmdir mystuff
cat file	display a file	cat myfile.txt
less file	display a file a page at a time	less myfile.txt
head file	display the first few lines of a file	head myfile.txt
tail file	display the last few lines of a file	tail myfile.txt
grep 'keyword' file	search a file for keywords	grep 'hello' myfile.txt
wc file	count number of lines/words/ characters in file	wc myfile.txt
command > file	redirect standard output to a file	cat > newfile.txt echo 'hello world' > myfile.txt
command >> file	append standard output to a file	cat >> newfile.txt echo 'hello world' >> myfile.txt
command < file	redirect standard input from a file	sort < myfile.txt
command1 \| command2	pipe the output of command1 to the input of command2	who \| sort
cat file1 file2 > file0	concatenate file1 and file2 to file0	cat file1 file2 > file3
sort	sort data	sort sort < myfile.txt sort > sorted.txt sort $lt; myfile.txt > sorted.txt
who	list users currently logged in	who
*	match any number of characters	ls txt ls myfile
?	match one character	ls ??file.txt
man command	read the online manual page for a command	man wc
whatis command	brief description of a command	whatis wc
apropos keyword	match commands with keyword in their man pages	apropos copy
ls -l	list access rights for all files	ls -l
chmod [options] file	change access rights for named file	chmod a+rw myfile.txt
command &	run command in background	sleep 10 &
^C	kill the job running in the foreground	^C
^Z	suspend the job running in the foreground	^Z
bg	background the suspended job	bg
jobs	list current jobs	jobs
fg %1	foreground job number 1	fg %1
kill %1	kill job number 1	kill %1
ps	list current processes	ps
kill 26152	kill process number 26152	kill 89

Reference: http://www.ee.surrey.ac.uk/Teaching/Unix/index.html

You can download MINIX, a clone of Unix for VirtualBox and try above commands.

Because of Unix's source code was widely available, various organizations developed their own versions of it. To make it possible to write programs that could run on any UNIX system, IEEE developed a standard for UNIX, called POSIX (Portable Operating System Interface). POSIX define a minimal system call interface that all Unix systems must support.

Minix

Minix is a small clone of Unix created by Andrew S. Tanenbaum in 1987. Minix was developed for educational purposes and included POSIX support. In 1991, a finnish student named Linus Torvalds started to develop his own operating system kernel on Minix which eventually became the Linux kernel.

Linux

Linux is a Unix-like, open source and community-developed operating system for computers, servers, mainframes, mobile devices and embedded devices. It is supported on almost every major computer platform including x86, ARM and SPARC, making it one of the most widely supported operating systems.

The Fourth Generation (1980–Present) Personal Computers

With the development of LSI (Large Scale Integration) circuits and introduction of microprocessor chips, the age of personal computers dawned. In 1974, Intel came out with the 8080, the first general purpose 8 bit CPU. Intel's one of the consultant Gary Kildall wrote a disk operating system called CP/M (Control Program for Microcomputers) for it. The OS was installed on an 8-inch floppy disk, making it the first microcomputer with a disk. Gary Kildall started Digital Research Inc. company and started to market CP/M OS to individual users.

In 1980s, IBM designed the IBM PC. After negotiations with Digital Research failed, IBM asked Bill Gates to provide an operating system for the IBM PC. Gates bought DOS (Disk Operating System), a clone of CP/M OS from Seattle Computer Products and hired the person who wrote DOS, Tim Paterson to make modifications for the DOS to meet IBM specifications. The modified system was named as MS-DOS (Microsoft Disk Operating System), Gates decided to sell MS-DOS to computer companies for bundling with their hardware. It is mainly developed targetting IBM x86 based personal computers.

Microsoft MS-DOS 6

Microsoft licensed MS-DOS to over 70 other companies. It could run on any 8086-family computers. MS-DOS was designed with a modular structure with internal device drivers, minimally for primary disk drives and the console, integrated with the kernel and loaded by the boot loader, and installable device drivers for other devices loaded and integrated at boot time. Command line interface was its default user interface. Following table shows mostly used DOS commands. Some of them still works in newer versions of Windows operating system.

Command	Meaning	Example
cd	change directory	cd Windows cd \Windows cd ..
dir	display available files and folder in current directory	dir dir .exe dir file dir fil?
copy	copy one or more files	copy .txt c:\ copy .* a: copy autoexec.bat c:\windows
del	delete one or more files	del test.tmp del c:\windows\test.tmp del c:\windows\temp\. del c:\windows\temp\?est.tmp
edit	a command line text editor	edit myfile.txt
move	move files or directories	move c:\windows\temp\. c:\temp
rename	renames files or folders	rename c:\computer hope
deltree	delete files and directories permanently from the computer	deltree c:\fake010
cls	clear screen	cls
format	erase information on a disk	format a:

Reference: https://www.computerhope.com/overview.htm

You can try above commands by downloading MS-DOS floppy disk images for VirtualBox.

In 1973, Engelbart who worked as a researcher at Xerox PARC developed the Alto personal computer, the first computer with a graphical user interface. It contained windows, icons, and menus (including drop-down menu) to support commands such as opening files, deleting files, moving files, etc. In 1981, Xerox introduced its pioneering product Star workstation. It was not commercially successful but influenced future developments of Apple, Microsoft and Sun Microsystems. Steve Jobs visited PARC realized the potential value of GUI. Apple released its first computer with GUI in 1983 called Lisa but it was too expensive. In 1984, Macintosh was released, with low-cost simplified design, it became commercially successful. Microsoft developed their GUI-based system in 1985 called Windows. Till 1995, Windows was just a graphical environment on top of MS-DOS. In 1995, a freestanding version of Windows, Windows 95 was released.

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