Glossary

UTXO

Unspent Transaction Output — a chunk of bitcoin that can be spent. Your node maintains the UTXO set to validate new transactions without trusting explorers. Heavy IBD work is largely about building this set efficiently (see dbcache).

Block

A batch of transactions sealed by proof-of-work. Full and pruned nodes download and verify every block during sync; pruned nodes may discard old block files afterward.

Peer

Another Bitcoin node on the P2P network. Zero peers means no sync. Check with getconnectioncount on the commands page.

Prune mode

Bitcoin Core discards old block files after validation, keeping recent blocks plus the UTXO set. Saves disk; does not skip IBD download. Guide: pruned vs full and disk full recovery.

Full node

A node that retains (or can rebuild) full chain history and independently validates consensus rules. Needs roughly terabyte-class storage in mid-2026 — check live sizes.

Mempool

Unconfirmed transactions your node knows about. Useful after you are near the tip; empty mempool during early IBD is normal.

RPC

Bitcoin Core’s JSON API (port 8332). Keep it on localhost. Never port-forward it. Details: security basics and bitcoin.conf.

IBD

Initial Block Download — first sync to the tip. Disk IO and bandwidth dominate. If percentages look frozen, read sync stuck before reinstalling.

Chain tip

The latest block your node considers valid. When blocks matches the network tip and verificationprogress ≈ 1.0, IBD is done.

Headers-first sync

Core downloads headers before full blocks so it can check proof-of-work cheaply before pulling heavy data. Headers ahead of blocks is often normal, not a hang.

Witness data

SegWit-related transaction data included in modern blocks. Affects historical size calculations after 2017.

Port 8333

Default Bitcoin P2P port. Optional inbound forwarding helps the network and reveals that you run a node. Not the same as RPC 8332.

Tor

Overlay network that can hide your node IP from peers. Optional and incomplete alone — Tor and privacy.

Electrum server

Indexer (e.g. electrs) so Electrum-compatible wallets can query address history against your machine. Not a substitute for Core validation — Electrum vs full node.

Block explorer

A website showing chain data. Convenient; you trust their server unless you verify with your own node.

SPV wallet

Simplified Payment Verification — typically relies on third-party servers for history instead of full validation.

Consensus rules

The checks every validating node enforces (signatures, supply schedule, difficulty, etc.). This is the point of running Core.

Bandwidth cap

VPS monthly egress limits. IBD can move hundreds of gigabytes once — plan on the VPS page.

dbcache

Config for UTXO cache RAM. Higher can speed IBD if you leave OS headroom. See conf reference.

AssumeUTXO

Advanced fast-start using a signed UTXO snapshot while history downloads in the background. Optional; most home nodes should prefer honest IBD on NVMe.

datadir

Directory where Core stores chainstate and blocks. Move it to a large volume when the OS disk is tiny — stop cleanly first.

verificationprogress

Approximate IBD completion from getblockchaininfo. Near 1.0 means caught up; plateaus can be normal — compare blocks over hours.

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