Absolute Loader Analysis Project

The Absolute Loader Analysis was the first project I carried out and it involved learning, instruction by instruction, how a program was loaded from a paper tape. This is a multi-step process involving firstly loading the bootstrap loader, which loads the absolute loader, which then loads whatever program you want to run. Paper tapes that store programs for use with the absolute loader need to be in a specific format, which is also described in this series of posts.

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• Part 1: provides an overview of the process and how loading a paper tape file can be emulated in SIMH.

• Part 2: describes in detail, instruction by instruction, the operation of the bootstrap loader.

• Part 3: describes the process by which the bootstrap loader loads and hands control to the absolute loader.

• Part 4: describes how the absolute loader loads and runs a program from tape

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Also as part of this project, I developed a utility to take a paper tape file, in absolute loader format, and extract all of the instructions that make up the actual program on tape. The utility can convert the paper tape into two output formats; either the set of SIMH instructions required to directly load the program in the emulator, or into a dump of the memory addresses and the values that will be placed into each memory address. Both output formats are very helpful for disassembling code from paper tapes.