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Wikipedia defines an execution unit as:

"In computer engineering, an execution unit (also called a functional unit) is a part of a CPU that performs the operations and calculations called for by the computer program."

  1. Now, is it a logical or conceptual thing performing the operations of the program? Or is it a physical (hardware) structure in CPU which performs the tasks called for by the program (e.g. shutting down the computer, changing the colors etc. ) ?

  2. And I have read that "In concurrent programming, there are two units of execution i.e. processes and threads."

Now, the concept I have made in my mind is that a unit of execution is, let's say a package of related classes as well as the system resources being used by them e.g. system's memory and other resources.

Please tell me to what extent am I right?

NOTE: Please keep your language (i.e. jargon and terminology you might use) simple enough for a beginner to understand.

Thank you in advance.

Solace
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1 Answers1

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It appears to me that execution unit refers to hardware, specifically a portion of the computer's brain that can work at the same time as other parts on a different task. It seems to allow simple multi-tasking, as implied by Wikipedia's article on the execution unit. The article explains that Superscalar Architecture involves multiple execution units fetching commands at the same time.

An execution unit is like a worker. He has a job and does it until he is finished. Then he asks his boss what to do next and works on that. When you have multiple workers, you get more work done faster. An execution unit does low level tasks like 1+1.

Moving onto unit of execution, it appears this is more about how the software runs, as evidenced by this microsoft article. A unit of execution, such as a thread, manages high level tasks involving many small steps like conquerTheWorld().

Aarowaim
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  • Thank you very much for your answer. I'll upvote it as soon as I get a reputation of 15. I need a bit of clarification: From your answer I have concluded that a unit of execution is different from an execution unit. I mean this is a bit difficult to take in, as in English both the terms should mean the same thing? – Solace Mar 12 '14 at 16:50
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    Thanks so much for the appreciation! To clarify: Semantically (grammar), they mean the same. They are two very similar ideas. They have a different flavour of the same meaning. So they are different, but not by very much. It's safe to say unit of execution or execution unit. Unless you write technical documents for universities (like this one: http://www.coastal.ca.gov/climate/slr/guidance/CCC_Draft_SLR_Guidance_PR_10142013.pdf) – Aarowaim Mar 13 '14 at 04:05
  • Both terms have this meaning: A small piece that executes instructions. – Aarowaim Mar 13 '14 at 04:07