The process of loading an operating system into a computer’s main memory called installation.

Starting the computer
The first operating system function would be starting the computer. When you start a computer, it loads the operating system into the computer’s RAM, which store the information as long as there is power. The process of loading the operating system to memory is called booting. There are two types of booting: cold and warm boot.

With a cold boot, you start a computer that has been powered off. In a warm boot, you restart a computer that is already on. The warm boots are often necessary after installing new software or after an application crashes or stops working. With both types of booting, the computer copies the kernel along with other essential portions of the operating system from the hard disk into the computer’s memory, where it remains while your computer is powered on and functioning. The kernel is the central part of the operating system that starts applications, manages devices and memory, and performs other essential functions. The kernel resides in the memory at all times, so it must be kept as small as possible. Less frequently used portions of the operating system are stored on the hard disk and retrieved as needed. Such portions are called non-resident because they do not reside in memory.

A cold or warm boot is a step-by-step process. In the following section, you will learn the steps performed by the computer after you initiate a cold or a warm boot (Figure 1.24).

Step 1: The BIOS (Basic Input/output System) and Setup Program
When you first turn on or reset a personal computer, electricity flows from the power supply though the central processing unit, which resets and searches for the BIOS. The BIOS is the part of the system software that equips the computer with the instructions needed to accept keyboard input and display information on the screen. The BIOS is encoded, or permanently written, in the computer’s ROM (Read-only Memory). ROM is a kind of memory that is permanent and unchanging. Programs such as the BIOS that are encoded in ROM are meant to be reliably used over and over again. In order to enter the BIOS, you have to press a key immediately after you turn on your computer. The magic key varies from computer to computer. You can probably find it by checking the specifications for your machine. Many computers write a message on the screen when the computer powers on, which tells you which key to hit to enter the BIOS. The most common keys are <Del>, <F1>, <F2> and <F10>. In some cases. you need to hold <Ctrl> and <Alt> and then press <Esc>, <Ins>, <Del>, <S> or <Enter>.

While the BIOS information is visible, you can access the computer’s setup program by pressing a special key, such as <Del> or <F8>. You will see an on-screen message indicating which key to press to access the setup program. The setup program includes settings that control the computer’s hardware. You should not alter or change any of these settings unless you are instructed to do so by technical support personnel. We will explore more on this setup program in “Step 3: Loading the Operating Systems”.

Step 2: The Power-On Self-Test (POST)
After the BIOS instructions are loaded into memory, a series of tests are conducted to make sure that the computer and associated peripherals are operating correctly. Collectively, these tests are known as the power-on self-test (POST). You may want to know the things that are tested in the computer. The components such as computer’s main memory (RAM), the keyboard and mouse, disk drives and the hard disk are tested. If any of the power-on self-tests fails, you will hear a beep, see an on-screen error message, and the computer will stop. You often can correct such problems by making sure that components such as keyboards, are plugged in securely.

However, some failures are so serious that the computer cannot display an error message; instead, it sounds a certain number of beeps. If this happens, it is time to call for technical support. To help the technician repair the computer, write down any error message you see and try to remember how many beeps you heard.

Step 3: Loading the operating system
Once the POST is successfully completed, the BIOS initiate a search for the operating system. Options in the setup program determine where the BIOS look for the operating system. These settings are set by default but can be modified by the user. On most personal computers, the BIOS first look for the operating system on the computer’s hard disk. When the BIOS finds the operating system, it loads the kernel into memory. At that point, the operating system takes control of the computer and begins loading system configuration information.

Step 4: System configuration
The configuration information about installed peripherals and software is stored in a database called the registry in Microsoft Windows. The registry also contains information about your system configuration choices, such as background graphics and mouse settings. Once the operating system’s kernel has been loaded, it checks the system’s configuration to determine which drivers and other utility programs are needed. A driver is a utility program that makes a peripheral device function correctly. If a peripheral device that is already installed on the system requires a driver to operate, that peripheral’s driver will be installed and loaded automatically. If the driver is missing, you may be prompted to insert a disk containing the needed driver.

Operating systems are equipped with Plug-and-Play (PnP) capabilities, which automatically detect new PnP compatible peripherals that you may have installed while the power was switched off, load the necessary drivers, and check for conflicts with other devices. Peripheral devices equipped with PnP features identify themselves to the operating system.

Step 5: Loading system utilities
Once operating system has detected and configured all of the system’s hardware, it loads system utilities such as speaker volume control, antivirus software, and a personal computer card unplugging utility. In Microsoft Windows, you can view available custom configuration choices by right-clicking one of the small icons located on the right side of the Windows taskbar. You can access additional system configuration choices in the Control Panel (Figure 1.26).

Step 6: Authenticating users
Once the operating system finishes loading, you may see a dialog box asking you to type a user name and password. Through this process, called authentication or login, you verify that you are indeed the person who is authorised to use the computer. Consumer-oriented operating systems such as Microsoft Windows and Mac OS do not demand that you supply a user name and password to use the computer. However, you can set up profiles on these systems. Associated with a user name and, optionally, a password, a profile is a record of a specific user’s preferences for the desktop theme, icons and menu styles.

On multiuser computer systems such as in a university lab or a corporate office environment, you must have an account to access a computer. Your account consists of your user name, your password and your storage space, which is called a home directory. The account is usually created by the computer’s system administrator, the person who is responsible for managing the use of the computer in multiuser systems.

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