format

[mohamed1]

when i download programs at the internet i cant open them. how can i know in witch format to open it.

[L0DER]

dude, no one can help you if you don't say which format you downloaded.
My personal guess is some kind of compressed file, zip, rar etc. If that's what you got, download Winrarhttp://www.rarlab.com/download.htm
You have to give a name.

[myhexhax]

Try using 7zip, it opens everything you can think of (zip, rar, bzip, tar, gzip, 7z, exe, iso...... of course, you probably don't want to use it on the last two lol)

Help us help you by providing us with vital information that we can utilize to help you help us help you!
(i.e. what's the extension of what you were trying to open?)

[Liquid_Obsidian]

http://en.wikipedia.org/wiki/File_format#Magic_number

try to figure out the first few bytes of your file

get a hex editor
Win : winhex or the one your like
*nix: hd (even better : file)... (but a little something says me that this very one line is superfluous...)

then look here :

http://www.garykessler.net/library/file_sigs.html

You're welcome...