ENVS 1500 Lecture 11: ENVS 1500 Lecture 11 Notes
13 May 2018
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ENVS 1500 Lecture 11 Notes – The barebones computer system
Introduction
• The material applies, to lesser or greater extent, to all of these.
• Interestingly enough, the convergence of these diverse areas has, itself, had a major
impact on the design and use of business systems.
• Consider once again the Little Man model that we introduced
• To use this model, a single program was stored in memory.
• The Little Man executed the program by executing each instruction in turn until he
encountered a HALT instruction, which stopped the computer.
• For simplicity, the Little Man scenario was designed to ignore several issues that must
be considered in a real computer.
• First, we assumed that the program was already loaded into memory, without
considering how it got there.
• In a real computer, the contents of RAM are destroyed when power is shut off.
• When power is again turned on, the contents of memory are initially unknown.
• Means must be provided to load a program when the machine is turned on.
• Remember that the CPU simply executes whatever it finds in memory as instructions
• So there must be a program in memory before the computer can even begin to execute
instructions.
• After the computer is on, there must be a method to load a program into memory any
time a new program is to be executed.
• Second, there must be a means to tell the computer to start executing the instructions
in a program.
• The Little Man began executing instructions whenever the location counter was reset to
zero.
• To lesser or greater extent, to all of these.
• Interestingly enough, the convergence of these diverse areas has, itself, had a major
impact on the design and use of business systems.
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