Bitcoin and Ethereum inter-block time difference

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I am wondering why Bitcoin's inter-block time is 10 minutes, whereas it is only about 15 sec in Ethereum. Given both Bitcoin and Ethereum are based on PoW consensus algorithm, why not decreasing the inter-block time in Bitcoin to be as Ethereum and thus increase the system througput?

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Terminator-Barbapapa On BEST ANSWER

The Bitcoin block time was chosen to make sure disk space would not become an issue.

Bitcoin whitpaper (2008): A block header with no transactions would be about 80 bytes. If we suppose blocks are generated every 10 minutes, 80 bytes * 6 * 24 * 365 = 4.2MB per year. With computer systems typically selling with 2GB of RAM as of 2008, and Moore’s Law predicting current growth of 1.2GB per year, storage should not be a problem even if the block headers must be kept in memory.

Another reason is to minimize orphan blocks. Which is a block that has been solved within the blockchain network but was not accepted due to a lag within the network itself. So the block is valid but broadcasted to the network too late. In the Bitcoin blockchain these orphan blocks go to waste, as the miner that mined it gets no reward for it. Which is a waste of computing power.

Also along with the wastage, if multiple nodes start generating the same block simultaneously or within a short period of time, this will lead into multiple and more frequent bitcoin forks, which is unhealthy for the network.

Ethereum, being a smart contract blockchain, needed a block time that was as fast as possible and solved this issue by introducing the Greedy Heaviest Observed Subtree (GHOST) protocol. This protocol included orphan blocks when finding the longest chain after a fork and it also rewarded the miners of these orphans blocks. So their computing power was not completely wasted.

TLDR: The use cases of the Bitcoin and Ethereum blockchains are different and Ethereum needs a faster block time to fulfill its purpose as a smart contract blockchain. A more detailed and technical explanation by Prabath Siriwardena can be found here: The Mystery Behind Block Time