BTC has a total supply of 19,495,156 million. Now the entire 19,495,156 are in circulation which means they are being held by holders/users.
No, the entire bitcoin is not yet in circulation.
I've been confused for a while on what happens to a particular cryptocurrency when swapped to another. I mean when a swap may be BNB to get usdt, what happens to the BNB?
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But another user can always swap another coin to BTC at anytime and receive the BTC, so where is the BTC coming from since it already in circulation (held by other holders)?
By swap, where do you conduct the swap processes? Centralized exchange like Binance? Decentralized Exchange (PancakeSwap, etc.)? or centralized swap platform (Changelly)?
The way of how it works is simply like a currency exchange, suppose X, a currency exchange company between EUR and USD. When you handover your money in EUR, in exchange for USD, X give you the money from their own reserves. So they did not magically hand or create the money out of thin air.
With that in mind, it also applies to many cryptocurrency swap processes.
Don't be confused, everything that happens in the cryptocurrency market is transparent and in time's of swap BTC to USDT is a function of liquidity provided in the exchange platform and is very already program in the crypto exchange platform or Dex platform.
Any interaction with a centralized entity is not transparent.