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I am not a computer specialist, but I have a keen interest in knowing things. And one the questions which piques my curiosity is:

  • What factors come into play for a computer to boot up fast?

I have used Windows, Ubuntu and Fedora, and I have seen that Windows, in quite slow, in terms of booting, whereas Fedora and Ubuntu boot up quite fast. Does, the booting speed depend on the OS, or does it depend on the CPU and other configurations.

And how does, having virtual Memory affect the boot speed.

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up vote 2 down vote accepted

A good portion of it is software set to run at startup. Over time as more and more programs get installed more and more gets added to the queue. If you were to compare a fresh install of Windows to a "used" one, you will probably see several programs added to startup and the newer installation booting much faster.

You can either use a program like CCleaner to see what's going on at startup or just type "msconfig" using the Run command line (win key + r).

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I agree! – user45535 Oct 26 '10 at 14:51
This answer miss a bunch of info related to boot fast factor. But... it's kinda true that, with Windows, you won't boot faster using msconfig but will get in windows quicker when everything is disabled. – r0ca Oct 26 '10 at 14:56

In general:

  • how many tasks do you have to do?
  • how fast can you finish one task?

So, the amount of time you need to finish ALL tasks is simply the sum of the time needed for each task.

Booting the OS is no different than any other problem: have a lot of tasks and it will take longer (Windows, lots of convenience services). Have only some tasks OR delay the start of the tasks a bit to give the user the feel of "the OS is booted already while it is actually not yet completely up" (Unix), then the boot process is much faster. Add a lot of tasks to the Linux boot process and it will be slows as well.

Add to that the fact that with a faster CPU, faster and more ram, a faster disk drive you can process data faster (resulting in less time needed per task) and you will have your answer.

Virtual memory: this slows down fetching data from the disk (since it puts more work onto the disk) when the system swaps processes in / out.

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Many Linux distributions, including Fedora and Ubuntu use ReadAHead to really speed up the boot process. ReadAhead Occasionally, the system will analyze what files are needed for boot (called profiling), and re-arrange and package them on the hard drive so that they can be accessed with the least amount of Hard Drive seeking. (basically, try to lay the boot files out in one long track). it loads all the files before they are even needed, then grabs them from memory later in boot, instead of from disk.

Windows has some similar concepts for the base boot, but it does not include services, and all those apps and tools running after you login. (like printer tools, antivirus, weatherbug, update checking tools, etc). these are the big reason windows loads so slowly. Windows 7 has gotten better, and one of the things added to windows vista/7, is the ability to have a "delayed start" of services once the computer is idle.

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Is it Read Ahead or RedHat – user45535 Oct 26 '10 at 14:52
It is read ahead. The file is read before (ahead) of when the file is needed. Although Redhat was a big developer of it. – Brian Oct 26 '10 at 15:13

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