IBM 2501

The IBM 2501 is a punched-card reader from IBM with models for the System/360 and System/370 mainframe systems and for the IBM System/360 Model 20, the IBM 1130 and IBM System/3 minicomputers. 2501 models can read 80-column cards at either 600 or 1000 cards per minute (CPM).^[1]

IBM 2501

Type	Punch card reader
Release date	1965; 60 years ago (1965)
Predecessor	IBM 1402
Related	IBM 2540

The 2501 is no longer sold, but is simulated in software on current IBM systems.^[2]

Models

The 2501 comes in four models depending on speed and attachment features. Models for mainframe use come with an integrated control unit that performs the functions of a control unit required by other devices.

The A1 and A2 are for the IBM 1130.^[3]

Model	speed (CPM)	Integrated control unit?
A1	600	no
A2	1000	no
B1	600	yes
B2	1000	yes

Usage

The 2501 uses a photoelectric sensor to read the data punched in the card. Cards are read serially (column by column) and the reader uses a simplified "straight through" card path. "Each column is read twice and the two readings are compared to check reading accuracy."^[4]

In a mainframe environment the 2501 was frequently used for mainframe input in an "open shop" environment where users submitted their own jobs.^[5][6]

On an 1130 system the 2501 can be used in addition to the IBM 1442. Since the 1442 has a maximum speed of 300 or 400 CPM attaching a 2501 provides a significant increase in read speed and lower CPU usage.

The System/3 normally processes 96-column punched card; the 2501 provides alternative input for shops that require the ability to read 80-column cards.

Features

A special feature (RPQ) is available for all models to allow them to read optically marked (OMR) cards.^[7]

See also

• Punched card input/output
• Computer programming in the punched card era