Bitcoin Basics · 1:33
What Is a Blockchain?
Is a blockchain high-tech magic? In about 90 seconds, Steady shows what it really is: a notebook of payments where every page carries a code from the page before, kept and checked by tens of thousands of computers.
Numbers in this episode
- ~10 min
- New pages (blocks) are added about every 10 minutes on average; the network adjusts the difficulty to keep that pace.
- Jan 3, 2009
- The first page, block 0 (the “genesis block”), is timestamped January 3, 2009, 18:15 UTC. It is the only page with no page before it.
- 970,000+
- Pages in bitcoin’s chain on October 10, 2026: the block height was about 970,790 (mempool.space and blockchain.info).
- 25,800
- Publicly reachable computers (nodes) keeping and checking a copy on October 10, 2026, according to btcnodes.io; many more run without being reachable.
- 4 of 64
- The page codes shown are real SHA-256 fingerprints of the pictured pages, cut to 4 characters. Bitcoin’s real block codes are 64 characters long.
- Satoshi Nakamoto, “Bitcoin: A Peer-to-Peer Electronic Cash System”, sections 3–5 and 11 (Nakamoto Institute copy)
- Bitcoin Core consensus rules (600-second block target)
- mempool.space, block height and the genesis block, October 10, 2026
- blockchain.info block count, October 10, 2026
- btcnodes.io, reachable nodes, October 10, 2026
- Blockworks, “Blockchains Are Not Immutable”
- Antony Lewis, “A gentle introduction to immutability of blockchains” (2016)
- The four-character page codes are computed: SHA-256 of the pictured page text, shortened
Transcript
Read the narration
Blockchain sounds like high-tech magic. It's really a notebook. A notebook of payments that thousands of strangers keep copies of.
About every 10 minutes, a new page is added, holding a batch of recent payments.
Here's the trick. Each new page starts with a code made from the page before it. Change one number on that page, and the code comes out completely different.
So every page is glued to the one before, all the way back to page one, written in January 2009. The pages are called blocks. A chain of blocks: a blockchain.
Now, say someone changes an old page to pay themselves. Its code changes, so it no longer matches the next page. The break runs all the way to today.
And they can't just swap in their copy. Tens of thousands of computers keep the same notebook and check every page. The odd one out is rejected.
To make a change stick, they'd have to redo every later page, faster than everyone else adds new ones. That's built to be extremely hard. The flip side: nothing gets erased, so mistakes stay in the record too.
So remember: a blockchain is a notebook of payments, each page glued to the one before, with copies everywhere. Next: who gets to write the next page? See you next episode!