All transactions on the bitcoin network are not created equally. A coinbase transaction is a unique type of bitcoin transaction that can only be created by a miner. This type of transaction has no inputs, and there is one created with each new block that is mined on the network. In other words, this is the transaction that rewards a miner with the block reward for their work. Any transaction fees collected by the miner are also sent in this transaction.
The First Transaction in a New Block
The coinbase transaction is, in most cases, the first transaction in a new block. The recipient of the coinbase transaction can choose to have the block reward, and transaction fees sent to one bitcoin address, or the bitcoins can be sent to a multitude of different addresses. In this sense, it’s just like any other transaction on the network.
The First Coinbase Transaction Cannot Be Spent
An interesting sidenote on this topic is that the first coinbase transaction from the genesis block cannot be spent. There are a few theories as to why this is the case, but it’s possible that this was simply an oversight by Satoshi Nakamoto, the creator of bitcoin. The issue here is that the original transaction was not placed in the transaction database. Although you can find the transaction in the blockchain, there is no way to spend bitcoins that cannot be found in the transaction database.
Spending the Bitcoins from a Coinbase Transaction
One last note to remember is that bitcoins in a coinbase transaction cannot be spent until they’ve received 100 confirmations in the blockchain. In some of the older bitcoin clients, it may not be possible to spend the bitcoins before 120 confirmations. All things being equal, 100 confirmations should equate to roughly 16 hours and 40 minutes.