IBM 2821 Control Unit
| Company type | Hardware component |
|---|---|
| Industry | Computer hardware |
| Founded | 1964 |
| Defunct | 1985 (in the United States) |
| Fate | Phased out |
| Headquarters | United States |
| Products | Interface unit for IBM System/360 and System/370 series; supports IBM 2540 card reader/punch, IBM 1403 and 1404 line printers |
| Owner | IBM |
| Parent | IBM |
The IBM 2821 Control Unit serves as an interface for connecting card readers and punches along with line printers to the IBM System/360 and IBM System/370 series of computers. It accommodates various configurations, including:
- The IBM 2540 card reader/punch;
- The IBM 1403 line printer models 2, 3, 7, and N1; and
- The IBM 1404 model 2 line printer as well as the bill feed printer.
Originally introduced in 1964 prior to the launch of the System/360, the 2821 managed the IBM 1402 card reader/punch as well as the IBM 1403 and IBM 2201 printers.
There were six distinct IBM 2821 models available:
- Model 1: equipped with one IBM 2540 and one IBM 1403;
- Model 2: featuring a single IBM 1403;
- Model 3: supporting two or three IBM 1403 units;
- Model 4: containing one IBM 2540 and one IBM 1404, compatible only with System/360 models 25, 30, 40, and 50;
- Model 5: comprising one IBM 2540 plus two or three IBM 1403 printers;
- Model 6: including one IBM 2540.
The unit is fully buffered, capable of storing complete cards or print lines for each device, thereby alleviating the channel from stringent timing constraints.
Connection is established through a byte multiplexer or selector channel, occupying one of eight control unit slots per channel. An optional two-channel switch allows attachment to two separate channels or systems, with control handled either manually or via programming.
Initially built primarily using IBM Standard Modular System (SMS) technology, subsequent versions integrated Solid Logic Technology (SLT) or Monolithic System Technology (MST) components. As logic component costs decreased over time, many of its functions were transferred into the central processor or directly into connected devices. The IBM 2821 was phased out in the United States market in 1985.