One possible candidate for the first commercial game to include a save feature that wasn’t dependent on a battery backup is Microsoft Adventure. This game is a port of the classic text adventure game Colossal Cave Adventure to the IBM PC. According to an answer to the Retro Computing SE question, "First commercial DOS game?", it is the first commercial game for the IBM PC. According to its manual, it allows saving to floppy disk (the manual uses the term "diskette"):
To Save Your Microsoft Adventure
A single exploration of Colossal Cave routinely takes several hours, which may be more time than you have at one sitting. For this reason, Microsoft Adventure includes the SAVE command to allow you to spread one game over two or more sessions.
To save your game, perform the following:
- Remove the diskette from the diskette drive, and then remove the write protect label (the small silver tab that wraps over the edge of the diskette). Simply lift up one edge and peel off the label.
- Reinsert the diskette into the diskette drive.
- Type SAVE and press ENTER. The computer will respond with SAVE CAVE IMAGE 1 OR 2.
- Type 1 or 2 and press ENTER. It makes no difference which number you pick unless someone else has already stored their partial game on one of the numbers. If you store on top of another game, the previously stored game will be destroyed.
- Once you have typed in 1 or 2, the computer will store your session on diskette and respond with Ok . You can now return at any time and resume the game where you left it.
- After you have finished saving your Microsoft Adventure game, remove the diskette from the diskette drive and replace the write protect tab over the notched edge of the diskette.
This suggests that Microsoft Adventure was one of the earliest commercial games, if not the first, to implement a save feature that did not rely on battery power.