THE BITCOIN BLOCKCHAIN
965,970 BLOCKS DEEP
The blockchain is one long list. A block is added about every ten minutes, and the list only ever grows at the end. It started on 3 January 2009, 17.7 years ago. Anyone can download all of it and check every line.
- BLOCKS SO FAR
- 965,970
- YEARS RUNNING
- 17.7
- MINUTES PER BLOCK
- 10
- LAST ONE, MINUTES AGO
- 14
- PAYMENTS IN IT
- 3,983
- ITS SIZE
- 1.69 MB
WHAT THE CHAIN IS
A block is a page. It holds a batch of payments and the fingerprint of the page before it.
Stack the pages in order and you have the whole record, from the first payment in 2009 to one made a few minutes ago. There is no summary and no shortcut. The record is every page.
Nobody keeps the official copy, because there is no official copy. Tens of thousands of computers each keep the whole thing and each check it themselves.
WHY IT ONLY GOES ONE WAY
Each page carries the fingerprint of the one before it. Edit an old page and its fingerprint changes, so the next page no longer matches, and neither does any page after it.
You cannot quietly patch that up. Every page after the one you touched has to be rewritten as well, and the world keeps writing new ones the whole time you are trying.
So the record is not protected by a rule saying nobody may change it. It is protected by what changing it would cost, and that cost grows every ten minutes.
WHY DEEPER MEANS SAFER
When people say to wait for confirmations, this is what they mean. Each new block on top of yours is one more page an attacker would have to redo.
One block deep is cheap to undo. Six blocks deep is not. A payment from 2015 sits under hundreds of thousands of pages and is, for any practical purpose, permanent.
And if two versions of the record ever compete, computers follow the one with the most work behind it. Not the longest, not the first. The heaviest.
QUESTIONS
How many Bitcoin blocks are there?
965,970 right now. The first was made on 3 January 2009 and one has been added roughly every ten minutes since.
How often is a Bitcoin block created?
About every ten minutes on average. The last one arrived 14 minutes ago. Individual gaps vary a lot; the average is what the difficulty rule holds in place.
Can the Bitcoin blockchain be changed?
Not quietly. Blocks are welded to each other, so touching an old one breaks every block that came after it. Making the change stick means outrunning the entire network while it keeps adding new ones.
How big is the Bitcoin blockchain?
Each block holds about one megabyte. The latest is 1.69 MB and contains 3,983 payments. The whole record from 2009 onwards is several hundred gigabytes.
Why do people wait for confirmations?
Because a payment gets safer the further it sinks. Every block added after it multiplies what reversing it would cost, which is why a shop picks a number of blocks and waits for it rather than trusting a promise.
Who owns the Bitcoin blockchain?
Nobody. There is no master copy. Tens of thousands of separate computers each hold the whole record and check it for themselves.
SEE IT RUNNING
The chain is one of the nine parts of the machine on this site: a line of blocks running back into the dark, one added every ten minutes since 2009.
THE PARTS NEXT TO IT
- BLOCK HASHThe fingerprint that welds one block to the next.
- NODESThe computers holding a copy each.
- MEMPOOLWhere a payment waits before it gets a page.
SMALL PRINT
This page describes a public network. It is not financial advice and quotes no price. Figures come from public Bitcoin APIs and may be a few minutes old.