#### Hey there! Welcome to another episode of Understanding the Blockchain.
You can check out previous episodes here:

##### 1. [Episode 1 | This Is How Money Works](https://peakd.com/hive-167922/@gamsam/this-is-how-money-works-understanding-the-blockchain-episode-1)
##### 2. [Episode 2 | Is Digital Money the Answer?](https://peakd.com/hive-167922/@gamsam/is-digital-money-the-answer-understanding-the-blockchain-episode-2)
##### 3. [Episode 3 | Before Bitcoin, Earlier Attempts at Crypto](https://peakd.com/hive-175254/@gamsam/before-bitcoin-earlier-attempts-at-crypto-understanding-the-blockchain-episode-3)
##### 4. [Episode 4 | Finally, Bitcoin!](https://peakd.com/hive-175254/@gamsam/finally-bitcoin-understanding-the-blockchain-episode-4)
##### 5. [Episode 5 | How is Crypto Acquired?](https://peakd.com/hive-175254/@gamsam/how-is-crypto-acquired-understanding-the-blockchain-episode-4)
##### 6. [Episode 6 | A Bitcoin Transaction in Depth](https://peakd.com/hive-175254/@gamsam/a-bitcoin-transaction-in-depth-understanding-the-blockchain-episode-6)
##### 7. [Episode 7 | What Happens When You Hit Send? ](https://peakd.com/hive-175254/@gamsam/what-happens-when-you-hit-send-understanding-the-blockchain-episode-6)
##### 8. [Episode 8 | An Overview of Mining](https://peakd.com/hive-175254/@gamsam/an-overview-of-mining-understanding-the-blockchain-episode-8-qdu39o)
##### 9. [Episode 9 | Introduction to Cryptography | Earlier Attempts at Cryptography](https://peakd.com/hive-175254/@gamsam/introduction-to-cryptography-or-earlier-attempts-at-cryptography)
##### 10. [Episode 10 | One Way Functions](https://peakd.com/hive-167922/@gamsam/one-way-functions-understanding-the-blockchain-episode-10)
##### 11. [Episode 11 | First Look at Hash Functions](https://peakd.com/hive-167922/@gamsam/first-look-at-hash-functions-understanding-the-blockchain-episode-11)

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<img src="https://cdn.pixabay.com/photo/2015/09/09/18/03/bullion-932218_960_720.jpg" alt="One-Way Functions">
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<h4>Hey! Welcome back</h4>

In the last episode, we talked about Hash Functions and what they mean. Today, I’ll be introducing another concept we need to understand to fully grasp how the blockchain works and that is the concepts of blocks.

The same way most application systems have a database, Bitcoin and other cryptocurrencies also have a database known as the ledger. The bitcoin ledger is made up of addresses of senders and receivers as well as the amount of bitcoin sent. There are a ton of transactions like this that make up the ledger. The actual ledger consists of over 300 million transactions on it all the way back to 2009.

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Now, as we discussed earlier, it is important that none of the information on any part of the ledger can be changed; the whole database needs to be secured. This can be achieved through fingerprinting with SHA-256 as we discussed in earlier episodes as well.

The problem now is that the whole ledger is over 200 gigabytes. SHA-256 fingerprinting the whole ledger would take an insanely large amount of time. Not only will it be done once, fingerprinting needs to be done whenever a new transaction is added to keep it up to date.

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##### HOW THEN DOES THE BITCOIN NETWORK HANDLE THE FINGERPRINTING OF THE LARGE NUMBER OF TRANSACTIONS?

### THEY BREAK IT INTO BLOCKS.

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In general, the network breaks the whole ledger into numerous blocks each containing about 2,400 which makes it about 1 megabyte per block. Remember the transactions are just a couple of pieces of information so it is incredibly easy to fingerprint a block. 

So, when new transactions are made, they begin to fill a block. When the transactions fill the block, the whole block is fingerprinted and saved and then new transactions start to fill up a new block. The approximate amount of time it takes for a block to be filled is about ten minutes. This keeps going on and new blocks keep getting fingerprinted. 


The key concept here is instead of one massive ledger, the ledger is broken into blocks every ten minutes approximately which are then fingerprinted individually instead of fingerprinting over 300 million transactions all at once.


<h4>Up Next</h4>

In the next episode, we’ll talk about what the term “blockchain” means.

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<h4>Resources</h4>

1.  "Blockchains: The great chain of being sure about things". The Economist. 31 October 2015. Archived from the original on 3 July 2016. Retrieved 18 June 2016. The technology behind bitcoin lets people who do not know or trust each other build a dependable ledger. This has implications far beyond the crypto currency."
2. Menezes, Alfred J.; van Oorschot, Paul C.; Vanstone, Scott A (1996). Handbook of Applied Cryptography
3. Trottier, Leo (18 June 2016). "original-bitcoin" (self-published code collection). github. Archived from the original on 17 April 2016. Retrieved 18 June 2016. This is a historical repository of Satoshi Nakamoto's original bit coin sourcecode"

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