I've heard of people losing bitcoin because they threw out a hard drive. And I've heard that you can control bitcoin with just a brain wallet (a memorized passphrase). Do you need just a passphrase, or do you also need a wallet.dat file (if you're not using an online wallet)? If someone could provide a simple explanation or point me to one I'd appreciate it.
This thread might be of interest:
https://bitcointalk.org/index.php?topic=488560.0I was a bit confused about this too but apparently, the private key is all that really matters. Your computer could burn to ashes tomorrow and you'd still be able to access your funds if you have your private key written down somewhere. In the case of brain wallets, a passphrase is memorized which is used to generate a unique private key but it's the private key that ultimately matters.
If you lose your computer but you have the wallet.dat file backed up somewhere then that can also be used to access your wallet since it contains the private keys of all the addresses in your wallet.
Some wallet programs like Electrum and Armory have a feature that lets you backup your entire wallet (ie. all your addresses and private keys) by writing down a short phrase called a seed. That way, if your computer is either lost or destroyed, you can still regenerate your wallet from this. Not sure exactly how it works though.