On 8/19/07, Michael Harpe <mharpe79@xxxxxxxxx> wrote: > The things that happen at power-up on most any modern computer are pretty > much the same. It's dictated by the need to start in an orderly, known > fashion every time. The idea of bootstrap programs go all the way back to > the very early days of computers. > > When you push the power button, the system power supply control logic senses > the closed switch and starts powering up the motherboard. On the motherboard > there is logic that brings up the chips on the board in the proper sequence. > > Once the CPU is powered up properly, the logic on the chip senses that a > power on reset has occured. The CPU logic is setup in a specific way such > that the chip starts in a prescribed manner each time. This is the key to > the whole process. > > What happens next varies by according to the individual chip architecture > but in general this is where the BIOS gets involved. > > The BIOS (BIOS means Basic Input Output System) resides in a EEPROM or FLASH > EPROM on the motherboard. This chip contains the program that gets the > machine started along with the low-level routines that interface the > operating system with the hardware on the motherboard. The CPU starts by > loading an address from the last (or first) few bytes of this ROM and > jumping to that address thus starting the boot process. > > What happens next is implementation dependent but basically consists of > setting the machine up to run an operating system and then loading the boot > block off of the selected boot device. This is usually the very first sector > of the hard disk. Once this is completed the same thing happens again, the > BIOS loads the program into RAM and jumps to it. > > Now we're into the loader for the operating system. The loader does more > preparation for running the OS and loads more of the OS into RAM. The next > step loads what's called the kernel, which is the core operating system. > From here you're running the operating system, be it Windows, Linux, > whatever. > > I hope this helps! > > Mike Harpe, N4PLE > Sellersburg, IN > If you want to know more try this site: http://computer.howstuffworks.com/ How a BIOS works is presented in this article: http://computer.howstuffworks.com/bios.htm
