This is the best block chain 101 video I've seen. Most often people explaining it don't sound like they understand what they're endeavoring to describe.

I salute a fellow stereotypical nerd

Best, most technically understandable explanation of the blockchain that I have ever heard.

This guy is brilliant. Finally someone who explained so clear with good enough knowledge but accessible for anyone who is not in the world of cryptocurrency and blockchain technologies.

It's interesting that the people criticising this guy's pronunciation can't post simple comment using correct spelling and grammar. Great video. I learned more in five minutes of this description than in a couple of hours worth of other videos.

Thanks for /finally/ taking the time to make a in-depth video about Bitcoin/Blockchain on Computerphile!

This video actually explained it to me. thank you. many podcasts and blogs have failed, but the whole public private key explanation made it click! thanks

Out of all the vague explanations about blockchains and cryptocurrencies available out there.. this is the best I have seen and most technically explained, and in a very short time.

He looks so nervous I want to give him a hug. Perfectly explained though

I have seen multiple simplified explanations of bit coins, the block chain and, mining and never understood it. Thank you Computerphile!

I already understood the components of this, but a clear brain-to-mouth presentation made it make sense (fully-ish). Thanks.

This is by far the best explanation of the system that I have heard yet. The ending of the video was rather sobering however. An hour or more to have a verified transaction is way too long for much of the world's trading, especially when we still have to pay a fee for the transaction.

I feel this would have been easier to understand if they had gone over version control system before this

This is the hardest Computerphile video to watch while eating cereal

Still mining 12.5btc per block till 2020. Much love to all involved in doing this vids!

This guys is very good at explaining the system Good job!

More on this topic please! And please talk about other implementations of the blockchain too. But Bitcoin is inherently interesting ofc.

for anyone interesed in learning more about bitcoin the princeton course available in youtube is very well done

Holy moly, I have watched many explanations on blockchain and this is the first one that made me go "Aha!". Thank you!

Great video. Hope to see you in more Computerphile videos!

Best explanation I've seen thus far. Fantastic video. -Cheers

Great video, would like to see more detail in the future about the network side of things behind this, like keeping track of transactions which were lost in a forked chain etc.

This is a MUCH better explanation of blockchain technology than his video on Smart Contracts.

wow. in depth and great explanation. Thank you!

I totally love that you write on a perforated computer paper.

His shirt is killing the antialias when you play it in a small window

Great video! Keep them coming! Just please pay attention: When looking for the merkle root C is duplicated and hashed with itself to get hash(C,C). It won't be hashed together with B!

The block reward is halved every 210,000 blocks (about 4 years), not every 21,000 bitcoins.

OMG hadn't seen dot matrix paper in more than 15 years, nearly cried :)

i watched the Video a 2nd time, the first time i was really impressed of such a cute pronouncing. But then i want to really know something about the Blockchain. And wow! by far the best technical Explanation of Blockchain here on KZfaq. Could be a bit more Graphical, but it is to 95% top! :D Nice work and keep up, i saw you made already an 2nd Video. Nice! i respect you a lot.

Excellent explanation of block chain. Thanks a lot!

it was a nice talk, from which i learned something. but it could use some more emphasis on practical details of: - how the concepts tie together - maybe just a tiny bit more about how public and private keys are normally used - could also mention that the sender chooses the transaction fee

very smart in explaining the process I loved it

brilliant video and well explained.

11:23 - Basically, if you mine a block but it ends up on the shorter chain, then you lose your block reward!

Is it necessarily the longest chain that wins? Couldn't I just create a longer chain in isolation on a reduced difficulty and then broadcast that chain to the network?

12:30 The txs on a fork chain are not "out of luck" or illegitimate(the block is orphaned or illegitimate the txs aren't), they simply go back into the mempool and get added to the next block on the valid chain. The end user isn't effected and he will get confirmations like normal.

Nice description of proof-of-work.

so many questions...who decides or sets the policy over how long the miners should take on average to decrypt the key? dont these people hold a lot of power over the bitcoin market? also, what if there arent enough miners around? then the transactions would take ages to validate, unless the keys are made easier to decrypt (which would mean constant adjustment of their difficulties?)?

will have a watch one more time cause it's high level for me! Thanks!

Each block is 12.5 Bitcoins right now, not 6.

I'm glad you guys managed to talk about "the blockchain" in 2017 by mentioning only bitcoin and leaving out ponzi schemes fraudulent securities and vaporware projects. However, despite the superficial overview about mining, one cannot talk about bitcoin and immutability without a more in-depth explanation about proof-of-work and how the process of burning energy is key to achieve that immutability and secure the network.

Very useful and detailed video!

Just what skynet needs. First, a distributed internet now a distributed currency.

Can someone tell me, in video description that mention about Note1, why the C is hashing to itself, not with B?

Great explanation! Thank you. :)

kripkee from big bang is here boys and girls. very well explained

So how does the value in USD come about?

I always thought that 'nonce value' meant the number of people in the Tory cabinet. Thanks for clearing that up!

thanks for this great explanation.

Can you make a new video explaining SegWit (and maybe the Lightning Network)?

Man this video solved my puzzle to understand blockchain you deserve a heart coin ❤.

Guys, why are you so mean? This man tells interesting stuff, he is definitely cool guy, why do you care so much about how he pronounces "s"?

Why is the puzzle where the miner varies the nonce value to eventually meet the hash criteria made to be so difficult? Is it to provide enough delay time for some process to prevent the same transaction getting grouped into two different blocks or something? Or just to slow down the mining process? I don't get it

I was hoping for information about the split. Good intro video though!

Great work !

Still a little confused about the nonce hash. Is the purpose simply to increase the computing difficulty of the blockchain creation?

This is a bit focused on crypto coins like Bitcoin used as cash. I recommend discussing blockchain tech for distributed computing, for instance, Ethereum.

i really like this subject, but i just realized i know very little about it...

How about a video on ethereum now?

Bitcoin is going through a turbulent time right now as miners can't currently achieve consensus on how Bitcoin should scale to increase .capacity for more transaction volume.

really well done!

Brilliant. I think I finally get (some of) it. Thanks.

amazing explanation, thank u very much

Very interesting video, very informative

Point of clarification in Bitcoin. It isn't the longest chain that defines bitcoin but the "Most worked VALID chain" that defines it. Bitcoin testnet and many alts have longer chains. Economic nodes define what is valid or not through consensus and the most worked is the combination of the cumulative weight on a chain of PoW (Proof of work)

Awesome video! Thanks!

I like to use blockchain and this video was cool but I am now more confused about how the system works

Great video!

This is a very brave man.

After many years I finally understand Bitcoin. Kinda. Thank you so much! :)

Thanks learnt a lot from this

Thanks for the explanation

I actually like his voice. Would like him to explain more things

Question: Who makes the criteria for the block puzzles? (Or how are they generated?)

Although they did not use the term blockchain, there existed software that proceeded Bitcoin that uses blockchains. One prominent example is git, and it's not a coincidence that it's also a distributed decentralised system.

brilliant,thank you!

There have been estimations about total power consumption of crypto-currency servers, miners, exchanges and cracking/manipulation attempts. The total electrical energy used far exceeds the net worth of, say, Bitcoin. Thoughts?

At that point in the future when miners are only rewarded for transaction fees, can miners decide to not incorporate transactions from the "ether" into their block if the transaction fee is too low or zero? Will that mean that, essentially, zero-fee transactions may have to wait longer until they are eventually confirmed into a block by a miner who does accept free transactions?

Just a quick comment on block halving. Current block reward is 12.5 and when it all started for BTC it was 50 BTC. Next year in April or May I think it will be half so 6.25 BTC then 3.125 BTC then 1.5625 BTC then 78.125 Million Satoshi then 39.062 Million Satoshi so on and so forth, that means it will take almost more than 7-10 decades to mine all coins. By then, I reckon it will evolve into something unknown.

I like to think of a Bitcoin wallet as owning the private key which corresponds to the transaction history on the distributed Bitcoin blockchain ledger of the coins held within it.

Doesn't this mean that the block-chain will become (close to) "infinitely" large eventually? I mean (eventually) 21 million bitcoins times whatever huge amount of transactions each day equals an enormously large block-chain? Even though it's only text, eventually not even NSA + GOOGLES + whatever, size of server is not going to be big enough to hold all this text?

Its like a database to which you can only insert and read... you cannot tamper with existing records.

Omg, you have no idea how useful this video is and how perfectly timed it is. I am applying for an apprenticeship at IBM and I researched Blockchain as it is one of their big things at the moment. This is exactly what I needed to learn further about it. THANK YOU!

So in a sense, the investments of real world currencies into this dedicated network infrastructure creates and supports the value of the digital currency, until those tx fees are supporting it. But won't another online currency be able to promise more growth and tease away capacity from BC? Fees might collapse a currency if they're too high, while not high enough to compete with mining rewards in (BC de novo).

5:50 when transactions are published in the network, it's existing out there in the ether. No pun intended.

at 3:16 this states that a bitcoin transaction is all or nothing. if I have 5 bitcoins and want to spend one I transfer 5 out, 1 to the person I am paying and 4 back to myself at 13:30 it states that transactions aren't really final until the are on the block chain and that takes about an hour. does this mean that if I spend some bitcoin I need to wait an hour before I can spend any more bitcoin, that would be really annoying, I regularly make 3-4 transactions within an hour on my credit card.

So distributed is not decentralized? Well explained video!

Would someone be so nice and add subtitles? I'm really interested in what he has to say, but I stand the way he talks.

This is the first time I heard about the fact that there will eventually be a maximum number of coins issued. That seems like an important piece of information. I also worry about what the mechanisms for actually making transaction fees work, will be. Another thing I wonder about is what the good safety practices are for actually using bitcoins, and currencies like it. Like, if you pay for something, using your cryto-currency of choice, what dangers are there, how might you be taken advantage of, and how do you make yourself harder to be robbed. I also wonder about how the use of a crypto-currency matches up with practicality, if you go to a physical store, but pay with a crypto-currency, will you have some kind of problem? I've never used, or even seen someone use, crypto-currency in a store. I heard somewhere that you have to wait for the transaction to clear, which could take ~10-30 minutes. (I don't have any solid evidence for or against it.)

So the actual bitcoins are actually just the result of the transactions? Not even an actual binary number? I guess the transactions are signed with the iniatiator's private key. Is that correct?

Just what _is_ "the ether"?

couldn't follow along from the block part :(

well, that takes courage. Lets hope internet will be nice to you.

So @Computerphile Core or Unlimited?

Wanna see my block chain? Panties hit the floor

Please do video on Monero

Great video! Concerning the "s" pronunciation problem, it seems you have a upper jaw front bridge, ask you dentist to create a small curved dip in the back of your bridge and you will be able again to make the sound "sss" again, there must be a small passage for air to make the correct sound. I had the same problem and corrected it like this. You should probably look for a more qualified dentist. I hope I am not making any mistake, only want to help.

wait...so the proof of work is just getting the nonce right? well...what keeps you from just making a transaction and telling a miner the nonce for that block?...or just confirming your own transaction?

Regarding this fork thing... If one network is big enough and favors the blocks computed by their own miners, couldn't this be exploited to first create a huge chain before making that one public? To outdo all other networks working on the blocks in question and "monopolize" the whole mining business?