Decentralized
A Bitcoin node is a pared-down computer that runs the Bitcoin software. There are tens of thousands of Bitcoin nodes distributed around the world. These nodes store the Bitcoin blockchain, the full list of all Bitcoin transactions that have ever occured.
For more info on the number of Bitcoin nodes:
Any change to Bitcoin protocol, including monetary policy, requires consensus among the nodes. There is no leader who can dictate policy. This quality is known as decentralization.
To ensure that Bitcoin remains decentralized, it's important that the amount of information in the entire Bitcoin blockchain is small (less than 400 GB in 2021). Otherwise heavy-duty machinery would be required to run a node. The small blockchain size means that only about 7 Bitcoin transactions can be processed each second.
The small blockchain size also means high Bitcoin transaction fees since the fees need to be spread across a relatively small number of transactions. In May 2021 the average Bitcoin transaction fee was $16 USD according to Bitinfocharts. This is quite reasonable for the high-dollar-value transactions that occur over the Bitcoin network. But it makes smaller payments impractical.
Bitcoin's base layer has the qualities of being very secure, somewhat slow (ten minutes for transaction confirmation) and somewhat expensive in terms of fees. However it plays the all-important role of keeping the network decentralized, and resistant to any change from individuals, companies or governments.
To make Bitcoin practical for day-to-day purchases the faster, cheaper Lightning Network was built on top of Bitcoin's base layer.
We'll explore Bitcoin's base layer and Bitcoin payment networks in two upcoming sections.