Saturday, December 5, 2009


Know The Difference Between Shutdown And Restart | Which One Is Safe And Effective

A shutdown simply powers down the machine almost entirely and does not attempt to start the operating system again until you press the power button. A restart simply ends your session, shuts the operating system down, and then re-loads the operating system again.

Common Use Of Shutdown And Restart:
1. Shutdown is used with the intention of leaving the computer in an off stage once the shutdown procedure has completed. 

2. Restart is used with the intention of recycling the current session of the OS, to reset applications running/hanging etc..
Personally speaking, I was always curious to know the technology behind a computer restart. Anyone can understand the process behind computer shutdown since we are habituated with the same kind of processes with our television sets, home theaters etc. But how do computers restart since it first closes down all running applications and gets shutdown, which means the power to the motherboard gets disconnected. Then how come it manages to restart the whole computing process from the beginning?

How Restart Works

Well, the answer is not that much confusing at all. When we shutdown our system (by pressing the power button or from the OS menu), our computer starts saving all data and then it starts dumping all RAM (Random Access Memory). Once the RAM gets dumped completely, SMPS cuts off power to the motherboard and that’s how a computer shuts down.

Now when we click the “Restart” button on our computer, the operating system starts shutting down all active and running programs to make the RAM free. Once the OS regains all RAM resources, it will issue a command to the CPU to warm boot where BIOS system takes over and controls the whole booting process. In this process, BIOS loads first 512 bytes of detected boot device, jumps to boot loader code and restarts the computer.

Few might have the misconception that shutdown process is safer while system restart might harm the computer. Well, if you have read the above explanation, you can conclude with the fact the computer restart makes our job more easier... But, is it safer?

Shutting down will prevent theft and data loss issues among other things. Re-starting will leave your computers available or open to many other risks.

There are a number of reason why we or programs go for shutdown or restart: 
Work stations should be shut down unless you are still running programs that process data that require hours to complete. It goes without saying if you shut down the machine the programs running will not complete their task and later you will have to start over.

I guess it will depend on the kind of lab and the purpose of each machine. Each machine may have a different purpose and that will dictate weather it needs to be shut down completely or not. 

And to be even Short, there is no effective difference between shutdown and restart. And technically speaking, A restart (at least in a Unix environment, which the Mac is), dumps EVERYTHING, and boots fully from a zeroed state. ALL processes are released and reinitiated from scratch. Even if there were anything residual in any cache, it would be overwritten anyway when the system was being restored.

I think the theory being put forward is that since some of the caps haven't fully bled off, there may be residual data in some of the registers. Unless they can state absolutely the decay rate of those, then "ten seconds", or any other SWAG'd delay, is basically bollocks.

This is more ancient technology concept, and since most Windows users have NEVER seen what actually goes on, process-wise, in detail, it's become more computer urban legend/dogma than anything else.

You could posit that a restart is easier on the microelectronics as they don't have time to suffer from thermal expansion because of short-cycle cooling  and reheating. That, as well, is debatable, but certainly a stronger theoretical argument than any nebulous "data left in cache" claim.


About bench3 -

Haja Peer Mohamed H, Software Engineer by profession, Author, Founder and CEO of "bench3" you can connect with me on Twitter , Facebook and also onGoogle+

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Write comments
December 6, 2009 at 6:51 PM delete

Really An Excellent Post. This is what i want to know as most used to say 'shutdown and leave 10seconds and start again.'

This is good, keep blogging!

April 17, 2012 at 9:44 AM delete

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