I keep hearing that the blockchain holds all of the Bitcoin transactions from the beginning of time. Where exactly is this file stored?
The blockchain is indeed a file that holds every Bitcoin transaction. It’s stored on many computers of Bitcoin users around the world, also known as Bitcoin nodes.
That’s what makes Bitcoin decentralized – there’s a copy of the whole system on thousands of computers. So no scammer can get one copy and rewrite it. In order to create such an attack you will need to rewrite thousand of copies.
If you’re using the Bitcoin core wallet then you too hold a copy of the blockchain on your computer.