The other day I was just toying around in Windows trying to write a C program
that could generate *ALL* the possible 4 letter words.
The motivation came from the fact that 75% of the people use even no of letters
in their passwords as they are easy to remember. Most sites specify 4 as the
min no of letters, so 4 is a good starting point (comparing with all 4 letter
words is an *extremely* cumbersome procedure for hacking a password however
important it is!! But we as novices cannot think at this stage about more
advanced techniques!!!!)
Coming back to our C program, it is extremely simple. We just have to loop 4
times changing from a to z.
Here is the main part of the program.
int i, j, k, l;
for(i=’a’;i<=’z’;i++)
{
for(j=’a’;j<=’z’;j++)
{
for(k=’a’;k<=’z’;k++)
{
for(l=’a’;l<=’z’;l++)
{
printf(’’%c%c%c%c\n’’, i, j, k, l); //u could also put this into a file.
}
}
}
}
This loop runs 26*26*26*26 times. 456976 times!!!! generating all the possible
4 letter words.
It starts with:
aaaa
aaab
aaac
.
.
..
aaba
.
.
..........
zzzz
I tried to output the words on the monitor using printf(). My machine is a P3
550Mhz with 192MB of RAM with TurboC 3.0( I assure u that it is really really
fast!!! Ask any guys if u doubt!).
Windows slogged through the procedure. I didn’t have the patience to wait till
it finished. I calculated that it takes approximately 676 seconds to output all
the words (Run this program in TurboC and see. The second letter of the word
changes once every second. So, the first letter changes once every 26 seconds
26 times thus making 26*26 = 676 seconds). It takes 11 minutes to run!!
The same program in Linux(I use Red Hat Linux ver6.2), the same printf() statement,
and LO!
The words fly by and it is done in 15 seconds (Just try it in Linux and see!).
Now, how is Linux 44 times faster than Windows?
Linux is moreover a multitasking system and our program gets a small chunk of
CPU time whereas in Windows our program runs unperturbed by others and yet,
Linux just races away. It definitely is a tribute to its unique architecture
and design which makes this possible.
I am finding out the exact reason for this although I have a vague idea.
Meanwhile, a small excercise would help. Instead of generating output on the
screen using printf(), open a file and try to store the words in the file. Now
run both the programs in Windows and Linux. What did u find?
The result will be interesting and throw some light upon why this happens.
Rest of this after I learn exactly about what is happening.