Guide | The Blockchain
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The Blockchain

What is the blockchain?

The blockchain is a file that contains a list of every bitcoin transaction ever made.

The blockchain

The blockchain

Everyone on the bitcoin network shares a copy of this file, and it updates regularly with the latest transactions.

The Bitcoin Network: Everyone sharing a file of transactions (called the blockchain).

The Bitcoin Network: Everyone sharing a file of transactions (called the blockchain).

Why is the blockchain important?

The blockchain tells you how many bitcoins each person owns.

This is because having a complete list of transactions allows you to work out how many bitcoins are located at each address. Therefore, you can figure out how many bitcoins each person has.

The blockchain is like a logbook, or a ledger.

Ledger – a book in which the monetary transactions of a business are posted in the form of debits and credits.

Why is it called the blockchain?

Because transactions aren’t added to the file individually. Instead, they are bunched together and added in blocks. Hence, blockchain.

Also, these blocks are linked together, so any changes made to a block lower down the chain will change the blocks above it. So _linked_blocks, or blockchain.

Transactions are added to in blocks, and these blocks are chained together.

Transactions are added to in blocks, and these blocks are chained together.

The block-ing of transactions makes it easier for everyone to share a copy of the blockchain. With the Internet connection speeds we’ve got, it’s much easier to share a file that updates once every 10 minutes, than one that updates multiple times a second.

The _chain_ing of transactions is a security feature. It makes it difficult to tamper with the blockchain without anyone noticing.

How is the blockchain shared?

The blockchain is shared by the nodes on the bitcoin network, in the same way a totally legit and non-copyrighted video file might be shared on the BitTorrent network.

Bitcoin peer-to-peer file sharing of the blockchain. If my file hasn’t got the latest blocks of transactions, someone will share them with me.

Bitcoin peer-to-peer file sharing of the blockchain. If my file hasn’t got the latest blocks of transactions, someone will share them with me.

P2P file sharing is a topic of it’s own, but for now just know that the blockchain is shared like a BitTorrent file across the bitcoin network.

Where can I get a copy of the blockchain?

You can get your own copy of a genuine, bona fide, electrified monorail blockchain by downloading the original bitcoin client.

Once installed and running, the client will connect to the network and start downloading the blockchain. It’s 20+GB, so give it some time.

When the download finishes you’ll have a complete copy of the blockchain, and a list of every bitcoin transaction ever made is in your hands. Furthermore, every time you run the bitcoin client you will be helping to share this file with everyone else joining the network. Some of your friends may even start calling you a “Full Node”.

By keerping a copy of the blockchain and sharing it with other people on the network, you make bitcoin stronger.

If you’re a fan of bittorrent, you could think of yourself as seeding the blockchain. Everyone loves a seeder.

Where is the blockchain file stored on my computer?

The blockchain is stored in files with names like this: blk00000.dat. There’s also blk00001.dat, blk00002.dat, and so on. (It’s split in to multiple files because it’s easier than working with one huge file.)

Their location depends on what operating system you’re using:

Linux
/home/[username]/.bitcoin/blocks/ Windows
C:\Users\[username]\AppData\Roaming\Bitcoin\ Mac
~/Library/Application Support/Bitcoin/

However, these .dat files contain data that is designed for a computer to read, so if you open one you’ll see a lot of mumbo-jumbo. But trust me, all the transactions are in there.

If you want to browse around a readable version of the blockchain, try http://blockexplorer.com. This website takes the data from the blk*.dat files (the very same copies you have), parses it, and makes a website out of it.

Greg Walker, 20 Feb 2015

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