Pruning a BTC node can only happen after downloading the entire chain.
Discussion
Yes because bitcoin nodes validate all tx and all blocks, unlikely Kaspa which is not trustless.
You can get a 1TB ssd drive for $60. This is after 15 years of activity, so obviously bitcoin does not have a storage problem.
Is it necessary that a node run the entire chain or is a partial node acceptable for some?
It depends on what you want the node to accomplish. There are different types of Bitcoin nodes, and not all need to download or store the entire blockchain:
Full Node: A full node must download the entire blockchain (currently about 570 GB) in order to validate all transactions and blocks. This ensures full independence and trustlessness, as the node validates all activity from the genesis block onward. Full nodes are considered necessary for those who want maximum security and trust in the network without relying on third parties.
Pruned Node: A pruned node also downloads the entire blockchain initially, but it does not store the full history permanently. It only keeps a set number of the most recent blocks (configurable, usually around 2-10 GB). This allows users to run a full-validating node with less storage but still participate fully in the Bitcoin network. Pruned nodes validate all transactions but don't retain the full history.
Lightweight (SPV) Nodes: These are "partial" nodes and do not download the full blockchain. Instead, they only download block headers (which are much smaller) and rely on full nodes for validation. SPV nodes offer a tradeoff between lower storage and less direct trust in the network but are acceptable for casual users who just want to send and receive transactions.
The main point being that you can run a full node with minimal hardware and capital investment. This is in contrast to Kaspa which requires millions of dollars of capital investment and colocation in a low latency data center to have any hope of running trustlessly.
And for trust, reliability, and use a partial node for most is sufficient, right?
no, a partial node is not sufficient for trustless use of the network.
Why?
Because a partial node can not validate all transactions and blocks, obviously. If you do not validate yourself, then you are trusting someone else to validate for you.
Don't trust, verify.
Yes, but not blocks of history, new blocks. Can they verify those?
A partial node can validate the block header but it cannot validate the transactions in the block.
And a pruned node?
yes a pruned node validates all blocks and all transactions. It is fully trustless. But because it is pruned it is not appropriate for something like a block explorer which may seek to view transactions and blocks that have been pruned.
But yes, pruned nodes are trustless.