[1] The 2501 is no longer sold, but is simulated in software on current IBM systems.

[2] The 2501 comes in four models depending on speed and attachment features.

[3] The 2501 uses a photoelectric sensor to read the data punched in the card.

"[4] In a mainframe environment the 2501 was frequently used for mainframe input in an "open shop" environment where users submitted their own jobs.

A special feature (RPQ) is available for all models to allow them to read optically marked (OMR) cards.