JOHNNIAC | 1953
The JOHNNIAC, developed by the RAND Corporation, was an early computer based on the von Neumann architecture, named in honor of John von Neumann. It stands for "John von Neumann Numerical Integrator and Automatic Computer." After being saved from destruction twice, it now resides at the Computer History Museum in Mountain View, California.
Technical Specifications
- Word Size: 40 bits
- Memory: Initially equipped with 1024 words of Selectron tube memory, each holding 256 bits of data. This was later upgraded to 4096 words of magnetic-core memory.
- Instruction Set: The machine had 83 instructions, with two instructions stored in each word, divided into 20-bit subwords (8-bit instruction and 12-bit address).
- Registers: Featured a single accumulator register (A) and a quotient register (Q). It lacked index registers and utilized a single test condition based on the high bit of register A.
- Weight: Approximately 5,000 pounds (2.5 tons).
Enhancements and Legacy
Numerous modifications were made throughout its operational life:
- Memory Upgrades: In March 1955, magnetic-core memory was introduced, replacing the Selectron memory. This change affected programs that used spare address bits for data storage.
- Drum Memory: A 12k-word drum memory was added later in 1955.
- Hardware Improvements: A transistor-based adder replaced the original tube-based adder in 1956, and a real-time clock was added in 1964 for time-sharing capabilities.
One significant legacy of the JOHNNIAC is the JOSS programming language (JOHNNIAC Open Shop System), designed for ease of use among novices. JOSS influenced later languages like DEC's FOCAL and MUMPS.
The CYCLONE computer at Iowa State University was a direct clone of the JOHNNIAC and instruction-compatible, while the ILLIAC I at the University of Illinois may have shared similar architecture. The CYCLONE was later enhanced to support floating-point arithmetic.
Overall, the JOHNNIAC represents a critical step in the evolution of computing, contributing to both hardware and software developments in the early days of computer science.
