Initial block download (IBD)

A new Bitcoin node must download and verify every block since 2009 before it is caught up. Learn what initial block download involves and how to speed it up.

Catching up on history

A brand-new node knows only the The genesis block. To reach today, it must fetch and verify every block since 2009 and rebuild the UTXO set. That's initial block download.

What takes time

• Disk speed and memory: the node constantly reads and updates the UTXO set. More database cache (the dbcache setting) helps a lot.
• CPU: checking signatures.
• Bandwidth: hundreds of GB to download.

A fast machine can finish within a day; a slow one with a hard drive can take much longer.

assumevalid

By default, Bitcoin Core skips signature checks for blocks buried under a known block hash shipped with the release. Everything else (amounts, proof of work, UTXO rules) is still fully checked, and the setting can be turned off to verify every signature. This speeds up IBD without trusting anyone for the money supply.

Using a node during IBD

Until it's synced, a node's view of recent blocks, fees and the mempool isn't current.

Speed-up tips

• Use an SSD, not a hard drive. This is the single biggest factor.
• Raise dbcache (for example 4,000 MB or more) if you have spare memory.
• Keep the computer awake and on a stable connection.
• Avoid running heavy tasks on the same machine during sync.

How long will it take?

On a modern desktop with an SSD, often under a day. On a small single-board computer, several days. Progress isn't linear: recent blocks are much fuller than early ones, so the last 20% takes far longer than the first.