Single-entry bookkeeping systems are all manual, paper systems. All computerized accounting programs are double-entry bookkeeping systems, which means that each financial transaction affects two general ledger accounts.
You may think that your computerized accounting program is a single-entry bookkeeping system because you only enter one general ledger account when recording the transaction. But your computerized system is a double-entry system because it automatically enters the information into the second general ledger account. For example, if you enter a check, the accounting program automatically deducts the transaction amount from your bank account balance. By selecting “check”, “withdrawal”, “deposit”, etc. the program automatically knows that a cash account is being affected and it automatically makes enters the transaction into the cash account. So, although you don’t see the accounting program assign a second general ledger account to a transaction, rest assured that the transaction absolutely does affect two accounts as required in a double-entry system.