Most of thesis specialized computers are located te centralized warehouses known spil mining farms. Many of them are located te China.
It’s also possible for individuals to mine bitcoin using laptop graphic cards or ASIC devices. However, due to the high difficulty level bitcoin is generally not profitable to mine for individuals.
The vast majority of individual mining done today, is done on the alternative currency side of the fence. Once the miner receives his altcoin, he can then exchange the coin into bitcoin. So this can be an zijdelings way to mine bitcoin and be profitable.
Here is a pagina containing a long list of currencies, most of which can be mined: Crypto-Currency Market Capitalizations