Web-based emulator for IBM 1620 Model-2 computer system released

IBM 1620 Model-2 Emulator Launch

A new web-based emulator has been released, providing an operating environment for the IBM 1620 Model-2 computer system. This emulator allows users to experience the functionality of the historic machine directly through a web browser.

The IBM 1620 Computer System

The IBM 1620 was a transistorized, decimal, variable field-length computer system from the 1960s, designed for scientific and engineering applications. Two models were produced: the Model 1 (1959) and the redesigned, object-code compatible Model 2 (1962). Approximately 2,000 systems were manufactured, with IBM supporting the series until 1970.

Architectural Details

The 1620 utilized a two-address, memory-to-memory architecture with no software-accessible registers. Instructions were 12 digits long, comprising a two-digit operation code and two five-digit addresses. The basic memory size was 20,000 digits, expandable to 60,000, with each digit containing a four-bit BCD value, a flag bit, and a parity bit. All arithmetic and data movement were performed digit-sequentially.

Model 2 Enhancements

The Model 2 improved upon the Model 1 with a memory cycle time of 10µs per two digits, half that of its predecessor. It featured hardware addition, while multiplication still used table lookup. Hardware division and indirect addressing were standard, and floating-point arithmetic remained an optional feature. The Model 2 also introduced options for index register address modification and support for binary bit-wise operations and octal/decimal conversion.

Peripheral Support

Initially, the Model 1 supported paper-tape and typewriter I/O. Later, the 1622 card reader/punch unit became available, followed by additional peripherals such as the 1443 line printer, 1311 disk drive with removable disk packs, and the 1627 plotter. These devices supported alphanumeric data input and output.