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Jaguar car
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  1. How many of them were making car payments on a Jaguar?
    • Many of them.
  2. How many of them knew assembly language?
    • Few of them.

Employment is still strong for computer scientists, who have a broad understanding of how computers work. The used car lots of Silicon Valley are full of Jaguars repossessed from people with superficial understanding of computers, now unemployed. (according to a recent news story).

Basic Machine Cycle

machine cycle

Most processors endlessly repeat three basic steps. Each machine cycle results in the execution of one machine instruction. A modern processor performs millions of machine cycles per second.

A machine instruction is a pattern of bits that corresponds to a fundamental operation of the processor such as adding two 32-bit integers together or testing if a value is zero. The details of the machine cycle differ between processor families. The machine cycle of most processor chips looks like the following:

Fetch the Instruction. The instruction is fetched from memory. The program counter (PC) is part of the processor. It shows where the instruction is located in memory.
Increment the Program Counter. The program counter now points to the next instruction.
Execute the Instruction. The operation asked for by the current machine instruction is performed.


In what order are machine instructions executed by the basic machine cycle?