2014 in review

The WordPress.com stats helper monkeys prepared a 2014 annual report for this blog.

Here’s an excerpt:

The concert hall at the Sydney Opera House holds 2,700 people. This blog was viewed about 15,000 times in 2014. If it were a concert at Sydney Opera House, it would take about 6 sold-out performances for that many people to see it.

Click here to see the complete report.

OS – Interview Preparation

Hi All,

Thanks for downloading(3000+ downloads) my ‘Best 100 Interview preparation pdf’ . I was requested to post some material for OS. I am not sure if these pdfs are still out there are Internet. I have collected them a few years ago, so uploading them here.

OS concepts

Segmentation And Paging

Concurrency Concepts

 

Funny facts about computers (compiled)

The first webcam was deployed at Cambridge University computer lab – its sole purpose to monitor a particular coffee maker and hence avoid wasted trips to an empty pot.

Although the MP3 standard was invented in 1991, it wouldn’t be until 1998 that the first music file-sharing service Napster, would go live, and change the way the Internet was used forever.

According to legend, Amazon became the number one shopping site because in the days before the invention of the search giant Google, Yahoo would list the sites in their directory alphabetically!

The nVidia GeForce 6800 ultra has 222 million transistors which is the record for the max. no. transistors on a chip.

One of every 8 married couples in the US last year met online.

In 1971, the first speech recognition software named, “Hearsay” was developed in INDIA.

Bill Gates’ house was designed using a Macintosh computer.

The average computer user blinks 7 times a minute, less than half the normal rate of 20.

The first domain name ever registered was Symbolics.com.

Tetris has sold over 40 million copies worldwide, since it began in 1982.That provided the creator 800 million in revenues.

The QWERTY keyboard layout is 129 years old.

The code name for the 12 engineers who designed the IBM pc was :-
‘The dirty dozen’.

The first popular web browser was called Mosaic and was released in 1993. 

Peter Norton of the fabled Norton anti-virus program once said that there was no such thing as a computer virus and considered the whole idea some sort of hoax.

Lenovo means “new legend” — “Le” for legend and “novo” for new.

Windows was originally named Interface Manager.

Views on Windows v/s Linux comparison

Windows and Linux has been ruling the hearts of computer users. But someone like a HR manager praises Windows for their GUI and someone like open source lover praises Linux.Both Windows and Linux come in many flavors. All the flavors of Windows come from Microsoft. Windows has two main lines. The older flavors are referred to as “Win9x” and consist of Windows 95, 98, 98SE and Me. The newer flavors are referred to as “NT class” and consist of Windows NT3, NT4, 2000, XP and Vista.

The various distributions of Linux come from different companies (i.e. Linspire, Red Hat, SuSE, Ubuntu, Xandros, Knoppix, Slackware, Lycoris, etc. ).

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Who starts faster? Linux/Windows?

In Linux, after the monolithic kernel has been loaded, the init process is started, which in turn invokes other processes. Practically, all the necessary system processes are started during the system start. So when a user sees login window (or screen) the only thing left to do is to attend to the KDE or GNOME graphical environments. Anything beyond that is ready to use.

In Windows, after starting the computer, the first thing which is loaded is a kernel indeed (ntoskrnl.exe). Next comes its best “friend”, namely HAL module – Hardware Abstraction Layer which manages drivers needed for system loading. When the environment is ready, a Session Manager is put into motion (smss.exe – Session Manager Subsystem) which starts identification and authentication programs – or using simple terms – which shows the login screen. A user satisfied that his Windows “is ready” to use, may enter a password, which makes the system load system permission data (Group Policy) and then have up and running the tasks defined in Runonce andRun keys placed in Windows Registry (e.g. HKLM\SOFTWARE\Microsoft\CurrentVersion\Runonce). At the end, Autostart (from Start Menu) applications are loaded.

Linux presents the login screen after everything is loaded whereas Windows presents it before the applications are loaded. Which one is better approach? Well, it’s like a user is psychologically pleased to see that OS is loaded in case of Windows. Though he know the fact that as soon as he enters password, he has to wait for apps to load. That’s not the case with linux. You enter password and its ready to use.

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Linux/Windows Kernel architecture – (Monolithic/Hybrid)

Linux is monolithic kernel with all functionality embedded into the kernel. The kernel is responsible for loading drivers, providing protection and handling access rights.

In Windows, the design is more like microkernel where kernel is not loaded with all functionalities. Its kept simple. However, we can call it hybrid and not microkernel because of helpers it needs while performing different tasks.

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Installation of new drivers :

On Windows, often the simplest changes to the system require a reboot, although sometimes this is more of a safety issue than an actual technical requirement. I would submit that this is one of the basic flaws of the MS operating systems. On Linux you could upgrade many of the driver modules and have little or not impact on the users. On Windows you might be required to reboot the entire box if you simply install a new application

The modular design of Linux also allows a system administrator to bring down a service, upgrade it and bring it back up without rebooting the operating system. In fact about the only time you must reboot a Linux operating system is when the kernel itself is being modified or upgraded.

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Protection :

In windows, protection is handled at user level. The protection subsystems are more complex and they run within the user layer. First of all, any program running in the user layer (protection is implemented as another program) is more vulnerable or prone to “disarmament” than protection implemented in the kernel layer. For second, one of the most popular computer protection systems, not playing with details, is a firewall. As it works in the user layer, it must be designed in such a way that it shouldn’t find itself not starting in the system’s loading process.

In Linux, safety tasks are run within the kernel layer.  Protection in Unix systems is always on, moreover, it is simple in terms of design and due to that statistically tougher to crack.

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At last, lets take a look at comparison with based on what pros and cons each of the OS has:

Windows :

Pros:

Compatibility: Almost every application, driver or game will work on Windows.

Technical support: Having so many users, you can always find someone (either online or offline) who can help you with Windows.Huge quantity of function: When you get to know Windows well, you’ll find out that there are so many functions that you can do almost anything quite easily.

Cons:

Viruses: You may need to buy an antivirus program, although free ones exist.

Slow: Windows, especially Vista and 7, requires a lot of computer resources (memory, processor, disk space), and thus, runs slower.

Price: It easily costs over a hundred dollars.

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Linux:

Pros:

Price: Linux is F-R-E-E. You can download it, install it, use it, modify it… All for a whooping 0$.

Variety: Linux is not a full operating system. It is just a kernel. To use the kernel, additional software needs to be bundled with Linux. Several hundreds of these bundles (called “distributions” or simply “distros”) exist. The most popular ones include Ubuntu, Mint and Fedora. The good thing is, with so many different flavours of Linux, there is always one to suit your needs!

Viruses: Although being more vulnerable to viruses than Mac (because it is open source), Linux still has very, very, very few viruses.

Cons:

Complicated: Although some distros are quite easy to use, most of them will required a good deal of computer knowledge in order to get them to work.

Compatibility: Like Mac, representing only a few percents of the market share, Linux does not have as many programs and games as Windows.

Vendors: You won’t find a lot of vendors selling Linux computers. Usually, you’ll just end up having to buy Windows computer, reformatting the hard drive, and installing Linux yourself.

In conclusion, no operating system is really better, the choice is up to you. If you’re a gamer, then you have no choice, go for Windows. Programmers might prefer Linux and video/graphics producers will probably tend towards Mac. The best thing to do is probably to try each OS and see which is best for you!

Interviews for higher education

What is the most common answer you get when you ask someone
about clearing interviews for pursing higher education in one of the best colleges?
“brush up your basics man”. Suddenly , lot of questions strike your mind at once but
you dont want to ask that. Well some of them are:
1. “Basics” means exactly what ?:-P
2. “Should i prepare all subjects” ?
3. “Should i mug up all definitions, examples
and real-life applications ?

Well, no you dont need to. Otherwise you will need one year to read
all the reference books just to revise all subjects. Brushing up basics means
when asked about certain topic from some subject, one should be able to express
what he learnt till date. Be honest and Say “you dont” know if you dont know it.
Just express what you know, do not try to express what you DONT know.

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Favorite subjects :

Sometimes people say ,”Just read about your favorite subjects thats it?”
No, be careful if you are preparing only your favourite subjects.
Sometimes , professors ask you about your favorite subjects and they will
not ask a single question about those subjects. ( Then you are dead , because
you get nervous. )
Just keep in mind, that they can ask you questions about any subject, so be
ready mentally to face questions. Someone can crack an interview surely, if he
is able to show that YES he wants to learn and study a lot.

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Confidence:

Be confident. Now, some people take this advice too seriously. Well here’s an
example :

Professor : You have opted for Mtech but not dual degree( Mtech + Phd 5 year course).
I think you should have opted for that.

Now, someone told the boy, always be confident and bold  in every answer you gave.
Speak truth always and express feelings without hestitation.
So the boys answers,

BOY:  Sir, trust me , I am not THAT kind of a guy.

Well, what he means by THAT kind of a guy? Such answer raises 1000’s of questions
in professor’s mind most of which are negative. Like,
– so the boy doesnt like people who do Phd
– the boy just wants to do Mtech for good salary and has no interest in studies.
– this boy doesnt like to study may be his parents forced him.
– n list goes on..
In short, dont be a DUDE out there, just be calm and answer like a decent guy.

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Answer carefully:

The professor asks you a simple question , and suppose you used heavy technical jargons
just to explain very simple concept then be careful. Each and every word that comes out
of your mouth, he is going to ask you questions related to those words.
So , if you say “Parser of a compiler interprets the grammar specified and analyzes syntax
of a program”. The professor will surely ask you next question as “what is grammar”?
And if you dont know that, BINGO ( professor – 1, you -0).

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Finally , to conclude i would say , just be calm and answer carefully.
Never be nervous by looking at students who keep on reading till the
last minute of interview. Its not that they want GEEKs or NERDs, they want person
willing to learn and still be a normal decent person.
So , be cool avoid getting tensed and start preparing. Best luck!!

Linux interesting commands

Hello readers,

Some commands that I personally find very useful are listed down here.
Internal and external commands
There are two types of commands in Linux.
1. Internal : These commands belong to OS , and does not
run an executable on firing them.
eg: cd
There is no executable for ‘cd’.

2. External : These commands when fired , shell performs
‘fork’ and ‘exec’. A new child process is created and the
corresponding executable is invoked.
These executables are searched in directories specified in PATH
variable.
eg: ls,which.

apropos
To use ‘man’ one must know , the command first and then he/she can
find details. What if you dont know the command at first place?
Use ‘apropos’. It searches in man pages for command whose description
will contain keyword specified with apropos.
To fire: apropos <keyword>

ls -l | cut -d ‘ ‘ -f2
CUT command can be handly when you want to display
a particular field or column of file contents.
Here , cut will display the first column ‘permissions’.
-d ‘ ‘ signifies the delimiter for separation of fields.

tee > a.txt
Most of the time ,we just need to write few lines
to some file , for some temporary person.
tee is handy in that case.
tee > a.txt will provide you prompt, write anything
and when you are done, press CTRL-D and it saves the content
to a.txt.
Advantage: Saves time , as you dont need to open

cat /etc/issue
This will help you to know about OS , currently being used on machine.

tar
Just archives the file , it never reduces size of the file.
so ten files, you tar it , then u get single file .tar with same size as that of
ten-files combined together.

Why to use ‘tar’ , why not use gzip or bzip2 directly?
Because , gzip/bzip2 operate on single file, and not on directory.
So , you need to ‘tar’ a directory then you get single file and
then you can use, gzip or bzip2 over it.

Shortcut: tar zcvf will ,’tar’ files and will also ‘gzip’ them to get ‘*.tar.gz’ .

bc
bc is an arbitrary precision calculator language.
If you want to caluclate 2^100 and such big calulations ,you can use ‘bc’.
It can perform square root operations in shell scripts. expr does not support square roots.

script
To record all the commands you run on promt.
Fire script and you will return to prompt.
Type commands you want to record , everything is written to file
name ‘typescript’ in current directory.
Usage: Employees can share certain steps to be executed by actually executing them
in their machines. Just fire ‘script’ before you start running commands’.
Once you are done, share typescript file with clients.

split
Split a large file into smaller chunks of some ‘x’ size.
split -b 2m bigfile MY_
This will split bigfile ( say of 100MB) into smaller chunks of
2MB whose names will start with ‘MY_’.

Background jobs
To start a background jobs : Add ‘&’ and end of command
ls ‘&’ : ls will run in background.

To view jobs running in backgroud:
jobs : this command will display background jobs with <jobid>.

To kill background jobs:
kill #! <jobid>

col
This command will help you to save man pages as plain text file.
man uname | col > uname_help.txt

Welcome

Hello Readers,

Thanks for visiting my blog. The primary purpose of this blog is to share knowledge and experiences with you all. Enjoy reading my blogs.