What is file extension in bitcoin wallet?

File extension has no relevance in bitcoin wallets. It can be any format. It's just a file which stores details like private key, public key etc. As a wallet developer, I can store keys and data in any format.

What is the Bitcoin data directory?

The data directory is the location where Bitcoin's data files are stored, including the wallet data file. Go to Start -> Run (or press WinKey+R) and run this:

Where can I store bitcoin data files?

You can also store Bitcoin data files in any other drive or folder. If you have already downloaded the data then you will have to move the data to the new folder. If you want to store them in D:BitcoinData then click on "Properties" of a shortcut to bitcoin-qt.exe and add -datadir=D:BitcoinData at the end as an example:

What is bitcoin banking and how does it work?

Unlike traditional banking where clients have only a few account numbers, with Bitcoin people can create an unlimited number of accounts (addresses). This can be used to easily track payments, and it improves anonymity. Advertised sites are not endorsed by the Bitcoin Forum. They may be unsafe, untrustworthy, or illegal in your jurisdiction.