Boot Up Process--Computer Learning --

Boot-Up Process:

A PC cannot do anything useful unless it is running its operating system - software that acts as a supervisor for all its software applications. It sets the rules for using memory, drives, and other hardware devices on the computer. Before a PC can run the operating system, it needs some way to load it from disk into RAM. The way to do this is with the bootstrap – a small amount of code that is executed on startup or system boot. The bootstrap is aptly named because it lets the PC do something entirely on its own  without any outside operating system.

 The boot-up sequence of events is as follows:

1. The computer loads the basic input/output system (BIOS) from ROM. The BIOS provides the most basic information about storage devices, boot sequence, security, Plug and Play (auto device recognition) capability and a few other items.

 2. The BIOS triggers a test called a power-on self-test (POST) to make sure all the major components are functioning properly. You may hear your drives spin and see some LEDs flash, but the screen, at first, remains black.

3. The BIOS has the CPU send signals over the system bus to be sure all of the basic components are functioning. The bus includes the electrical circuits printed on and into the motherboard, connecting all the components with each other.

 4. The POST tests the memory contained on the display adapter and the video signals that control the display. This is the first point you’ll see something appear on your PC’s monitor.

5. During a cold boot the memory controller checks all of the memory addresses with a quick read/write operation to ensure that there are no errors in the memory chips. Read/write means that data is written to a bit and then read back from that bit. You should see some output to your screen - on some PCs you may see a running account of the amount of memory being checked.

6. The computer loads the operating system (OS) from the hard drive into the system’s RAM. That ends the POST and the BIOS transfers control to the operating system. Generally, the critical parts of the operating system - the kernel - are maintained in RAM as long as the computer is on. This allows the CPU to have immediate access to the operating system, which enhances the performance and functionality of the overall system.