Hi!
I can't seem to understand what exactly are registers.

Well, thats all I know. I know that I can store a variable in it, and I know that there are 8 bit and 16 bit registers. For example there are: AX - accumulator, BX - BASE etc.. Isn't they the same?

For example when I want to output text in DOS, I store value 9 into AH register and address of my variable that contains text into DX register. Why can't I store my address of my variable in BX register, and how does DOS know in what register I store my message?

There are also segment, index registers! What are they? Why are they so many? and what is the purpose for each register? Can anyone please explain me this? Or does anyone know any newbie friendly tutorial about this? Thank you!

[Matrix_Spell_Checking=adjust;reason="For Better searching"]Matrix[/Matrix_Spell_Checking]

DOS doesn't "know" anything
THAT is the reason you cannot put it in bx or any other,
because DOS always takes the ax register as input.

I think you answered your question yourself there

you don't need to touch segments very often (at least in 32bit mode)

I think you have to read some tutorials, because we cannot
explain all to you in these forums.

Thank you!
Now please can you suggest me any fasm tutorials? I have read this http://decard.net tutorial. Thank you!

I guess you haven't read any tutorials or searched the boards
http://flatassembler.net/docs.php?article=manual
http://board.flatassembler.net/topic.php?t=2530
http://board.flatassembler.net/topic.php?t=2527
...
another good resource is
http://webster.cs.ucr.edu/
Check out the AoA book and some windows programming resources

i also recommend you reading the basics before asking something, this board is not large enough to contain every basic questions like what is byte? or similar.

you should also take a look @
Flat Assembler Frequently Asked Questions (FAQ) (main)

its linked to other FAQs as well, and they should contain a large amount of links to tutorials. if you find tutorials explaining your problem well you can recommend them @ faq page like:

"i found this great tutorial about xxxx @ http://xxxx.com/whatisit.htm,
and you should add it to your faq."

this way it others have the same question, they will find it easily without searching in the FAQ

well i see your thread is already DUPE,

http://board.flatassembler.net/topic.php?t=2592

why do you post same question multiple times?