How big can the block chain become? It's already 7 GB after a couple years!
The block chain length in number of blocks will grow indefinitely with one block being created for 10 minutes on average.
The actual size of the whole chain will strongly depend on the following two aspects:
- the number of transactions
- how the block chain will be stored across clients
Since the speed with which the block chain grows has been slightly increasing since the beginning of Bitcoin and the block chain is already significantly big, some of the Bitcoin developers have been considering to implement a solution for this that would make it unnecessary to keep a history since the beginning of time.
Currently already the standard Bitcoin client compresses the block chain for storage. The older blocks become, the more they are compressed. This means that you required less disk space to store the block chain, but also that it takes longer to start building it from scratch. Other clients have to decompress it to share it with you and you will have to compress everything you receive. This results in the fact that new clients often need multiple days to get in sync with the network.
The blockchain will continue to grow over the years. It depends on how much data people put into it. There is some upper limits set right now, but they will likely be changed once Bitcoin grows so popular we need more space.
Therefore it stands to reason that eventually users will not download the blockchain themselves, but collectively do that. Via Bitcoin wallets for example. Or use light clients that have no copy of the chain themselves.
It is expected to remain "affordable but ineffective" for the time to come. Also given an extensive form of blockchain-pruning can reduce the blockchain's size, but hasn't been implemented for a lack of priority.
I know two things for sure: 1) The blockchain will continue to grow. and 2) when I installed the Bitcoin core yesterday, on a fresh new computer, it told me to allow for the initial amount to be 80GB. For me, the only reason that matters is because I get charged extra by the cable company. And it also tells me how long to expect it to take before that original load is finished.
The OP said it was 7GB in 2013.
So yes, #1 is true - it will grow.
So the wild card appears to be the work factor doubling this summer. The last time it doubled was 2012. But that was before the big guns started mining.
As it becomes more expensive to mine for the same earnings, it should be obvious that there will be fewer miners, which translates into longer clearance times. In fact, we're seeing it already as people position themselves for the new reality to come.
The good change is that the powers that be are also considering doubling the block sizes. That will translate to longer times before transactions get posted and verified.
Yet the blockchain size may continue to grow at a linear rate.
So I am curious about the basis for this question. The OP didn't explain why the size of the blockchain was of interest.
Speaking for myself, I believe the longer clearance times will totally devastate the nascent BTC economy. We'll never see transaction rates like VISA (thousands per second). 6 months ago the blockchain wasn't even quite at 100 tps.
Face it, dealing directly with the blockchain at the point of sale will never work - your coffee would get cold long before the store could be sure you had the ability to pay. This is why third party card issuers can work to keep blockchain issues from spilling over to customer service issues.