https://en.bitcoin.it/wiki/Running_Bitcoin
Loading bootsrap.dat torrent
Downloading the bootstrap.dat file is just as secure as downloading the blockchain from peers, but since all the data is already there, the only latency you suffer between blocks is going to your hard drive and finding the next block.
You simply need to place the bootstrap.dat in your %appdata%\Bitcoin folder, (on linux/unix in your .bitcoin folder). The file will be renamed to bootstrap.dat.old when the data import is complete. Using this, it took me only 4 hours to catch up with the network, as opposed to the 1-2 weeks it took me before reformatting on the same computer.
from stackexchange
https://bitcoin.stackexchange.com/questions/21473/how-can-i-import-blockchain-dat-into-bitcoind