Can you store bitcoin on a USB drive?

Yes, you can store bitcoin on a USB drive in the sense that you can keep a wallet file or key backup on one. The bitcoin itself is not on the drive. As Trezor's guide puts it, coins are held on the blockchain, and what any wallet stores is the private key that lets you spend them.

Can bitcoin be stored on a hard drive?

The same logic applies to a hard drive, a USB stick or a memory card. Desktop wallets save their keys in a file on the computer. Bitcoin Core keeps wallets in a folder inside its data directory, and Electrum saves a file called default_wallet in its own data folder. Copy that file to an external drive and you have a backup that can restore the wallet later.

Bitcoin Core's documentation says backups can sit on one or more offline devices, as long as they are reliable enough to work in an emergency and free of malware. It also warns that if the wallet and every backup are lost, the coins become permanently inaccessible. Many modern wallets instead rely on a seed phrase, and writing those words down can replace a file backup.

Is a USB stick a hardware wallet?

No. A hardware wallet is a small computer of its own. Trezor explains that the device signs each transaction internally and asks you to confirm it on the device, so the private key never leaves it.

A USB stick has no screen, no buttons and no chip that signs anything. To spend from a wallet file stored on it, you plug it into a computer and open the file there, at which point the key is exposed to that machine. If the computer is infected, the key can be copied. Products sold as a "USB crypto wallet" vary, so check whether a device signs transactions itself or just stores files.

How do you store a wallet file offline safely?

The guidance from Bitcoin.org, Bitcoin Core and the Bitcoin Wiki points in the same direction:

• Encrypt it. Bitcoin Core's wallet file is not encrypted by default, and its encryption covers only the private keys, so the transaction history stays readable. Electrum encrypts its wallet file by default.
• Remember the password. Bitcoin.org says a forgotten wallet password means the funds are lost. Electrum says it cannot recover a password, though the seed can restore the wallet.
• Keep more than one copy. The Bitcoin Wiki suggests encrypted copies in two or more safe places, weighing theft, fire and natural disaster.
• Back up again after changes. Bitcoin Core says to make a fresh backup after encrypting or changing the passphrase, and to test backups from time to time.

What are the limits of a USB backup?

A drive can fail, get lost or be wiped by accident, which is why multiple copies matter. Wallets that do not derive every address from one seed also need regular new backups, Bitcoin.org notes. For a broader comparison of storage methods, see hot wallet vs cold wallet, and for an older offline method with its own risks, see what a paper wallet is.