September 09, 2010
How does a Computer work from boot up to shut down?
Posted by: kk : Category: Computer Question Answers
Can someone explain what happens to a computer while the computer is booting up? Some general description of the products that are used during the boot up process. That would be helpful thanks.
September 9th, 2010 at 9:49 pm
When you press the on switch it sends a signal to your motherboard which instructs it to use the power from the power supply unit. The motherboard then sends power to all connected components and transfers data to and from your central processing unit (CPU), graphics card and hard disk drive (HDD).
The Bios (basically all the settings you config when you enter setup upon booting your pc) which is stored permanently on your motherboard then sends info to your cpu which is then processed to start up the computer, as this happens the motherboard communicates with the graphics card to tell it to draw pixels to show the image of the screen, this is then transferred to the monitor which shows the end result.
The motherboard then checks for a small file (boot record) on your HDD which tells it that an operating system is installed (or more than one if this is the case)
If this file is there it loads up the operating system (or if 2 are installed it shows a menu asking which one you would like to use)
if no operating system is installed it checks for other boot methods (customisable in the bios setup)
these are usually floppy disk drive, cd/dvd/bluray rom, usb HDD and network boot.
There are also loads of other checks performed during startup, a computer performs many yes/no checks everytime it does any processing whatsoever, such as; is this component plugged in? and if the mhz selected in the bios for a certain component is stable upon boot.
Upon reaching the operating system and logging in the system then loads kernel (core of the operating system) processes and then the ones selected to load upon startup in the systems config file. Usually antivirus and firewalls load early to try and detect any unwanted boot processes.
Upon shutdown, the system checks for any currently running processes and attempts to close them if it is safe to do so, if after a long period of time the process still has not closed most operating systems will ask the user if they want to close the process or keep waiting.
When only kernel (core operating system) files are left, the operating system can then safely shutdown the computer.
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