Lesson plan
Lockheed MAC-16
The MAC-16 (or LEC-16) was a 16-bit minicomputer introduced in 1969 by Lockheed Electronics. One main selling point of the MAC-16 was a dedicated context switching system that completed operations in two machine cycles. Several improved versions were introduced, including the MAC Jr., Sue, and System III, but the company dropped support for all of these in the late 1970s. The MAC-16 was designed to support various high-performance military and civilian roles, and thus spent a considerable amount of time on guaranteeing high speed context switching to support real-time computing. A switch to and from an interrupt handler took only 2 cycles. The original MAC-16 operated with a 1 μS cycle time using core memory and TTL integrated circuits. Lockheed advertised the machine with the slogan "In by 12:34:45.000000, out by 12:34:45.000002". The system featured 64 interrupt levels, allowing considerable flexibility in software design. Like any machine based on a 16-bit instruction register, the original MAC-16 was able to address up to 64 kilo-words (kW, 128 kB) of RAM. At the time, RAM was provided in the form of hand-wired core memory, which cost about $1 per word. Most MAC-16 machines thus featured considerably less than 64 kW, and 8 kW systems were common as this was all that was needed to support a Fortran compiler.…
Article summary
The MAC-16 (or LEC-16) was a 16-bit minicomputer introduced in 1969 by Lockheed Electronics. One main selling point of the MAC-16 was a dedicated context switching system that completed operations in two machine cycles. Several improved versions were introduced, including the MAC Jr., Sue, and System III, but the company dropped support for all of these in the late 1970s. The MAC-16 was designed to support various high-performance military and civilian roles, and thus spent a considerable amount of time on guaranteeing high speed context switching to support real-time computing. A switch to and from an interrupt handler took only 2 cycles. The original MAC-16 operated with a 1 μS cycle time using core memory and TTL integrated circuits. Lockheed advertised the machine with the slogan "In by 12:34:45.000000, out by 12:34:45.000002". The system featured 64 interrupt levels, allowing considerable flexibility in software design. Like any machine based on a 16-bit instruction register, the original MAC-16 was able to address up to 64 kilo-words (kW, 128 kB) of RAM. At the time, RAM was provided in the form of hand-wired core memory, which cost about $1 per word. Most MAC-16 machines thus featured considerably less than 64 kW, and 8 kW systems were common as this was all that was needed to support a Fortran compiler.…
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Discussion questions
- Summarise the article in your own words. Which single claim would you verify first, and why?
- Which claim in this article is most likely to be revised as the sources update? How would you check its current status?
- If two sources disagreed about one of these facts, what would you need in order to trust one over the other?
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