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BINAC, the Binary Automatic Computer, was an early electronic computer designed for Northrop Aircraft Company by the Eckert-Mauchly Computer Corporation in 1949.

The BINAC was a bit-serial binary computer with two independent CPUs, each with its own 512- word acoustic mercury delay line memory. The CPUs continuously compared results to check for errors caused by hardware failures. It used approximately 700 vacuum tubes. The 512-word acoustic mercury delay line memories were divided into 16 channels each holding 32 words of 31 bits, with an additional 11-bit space between words to allow for circuit delays in switching. The clock rate was 4.25 MHz (1 MHz according to one source) which yielded a word time of about 10 microseconds. The addition time was 800 microseconds and the multiplication time was 1200 microseconds. New programs or data had to be entered manually in octal using an eight-key keypad. BINAC was significant for being able to perform high-speed arithmetic on binary numbers, with no provisions to store characters or decimal digits.

The BINAC ran a test program (consisting of 23 instructions) in March 1949, although it wasn't fully functional at the time. Here are early test programs that BINAC ran:

• February 7, 1949 - Ran a five-line program to fill the memory from register A.

• February 10, 1949 - Ran a five-line program to check memory.

• February 16, 1949 - Ran a six-line program to fill memory.

• March 7, 1949 - Ran 217 iterations of a 23-line program to compute squares. It was still running correctly when it stopped.

• April 4, 1949 - Ran a fifty-line program to fill memory and check all instructions. It ran for 2.5 hours before encountering an error. Shortly after that it ran for 31.5 hours without error.

Northrop picked up BINAC in September 1949. Northrop employees said that BINAC never worked properly after it was delivered, although it worked at the Eckert-Mauchly workshop. It was able to run some small problems but didn't work well enough to be used as a production machine. The failures were attributed to it not being properly shipped when Northrop picked it up.

• Unisys History Newsletter Volume 5, Number 1
• Roger Mills' Description of the BINAC

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