Computer startup process

The PC start-up process 

When you turn power on, several things happen in the PC:
●   You hear the fan motor starting. There are one or more cooling fans in the PC. They produce a whirring sound.
●   After a few seconds, text starts to scroll on the screen.
●   Now the PC tests and counts the RAM. You see a number on the screen. It increases in size.
●   To understand the working of the PC, it is useful to study the PC start-up process. Those are events, which take place from power-on until the PC is ready to work. Remember, the PC can do nothing without receiving instructions. These instructions are commands, which are sent to the CPU. During start-up, the PC reads the commands in this sequence:
●    First it receives commands from the ROM chips. Those chips are inherent in any computer. They contain the POST and BIOS instructions, which we will look at shortly.
●   Next, the operating system is read from the hard disk (or from floppy drive A). This is called the boot process.

The ROM chips 

ROM (Read Only Memory). The ROM chips are on the system board. They contain. system software. System software are instructions, which enable the PC to coordinate the functions of various computer components. The ROM chips contain instructions, which are specific for that particular system board. Those instructions will remain in the PC throughout its life. They will usually not be altered. Primarily, they are start-up instructions. There are different parts in the start-up instructions. For most users, they are all woven together. You can differentiate between:
●   POST (Power On Self Test)
●   The Set-up instructions, which connect with the CMOS instructions
●   BIOS instructions, which connect with the various hardware peripherals
●   The Boot instructions, which calls the operating system (DOS, OS/2, or Windows)
  All these instructions are in ROM chips, and they are activated on by one during start-up. Let us look at each part.

POST

Power On Self Test is the first instruction executed during start-up. It checks the PC components and that everything works. You can recognize it during the RAM test, which occurs as soon as you turn power on. As users, we have only limited ability to manipulate the POST instructions. But certain system boards enable the user to order a quick system check. Some enable the user to disable the RAM test, thereby shortening the duration of the POST. The duration of the POST can vary considerably in different PC's. On the IBM PC 300 computer, it is very slow. But you can disrupt it by pressing [Esc]. If POST detects errors in the system, it will write error messages on the screen. If the monitor is not ready, or if the error is in the video card, it will also sound a pattern of beeps (for example 3 short and one long) to identify the error to the user. If you want to know more of the beeps, you can find explanations on the Award, AMI and Phoenix web sites. POST also reads those user instructions, which are found in CMOS:

CMOS

CMOS (Complimentary Metal Oxide Semiconductor) is a small amount of memory in a special RAM chip. Its memory is maintained with electric power from a small battery. Certain system data are stored in this chip. They must be read to make the PC operable. There may be 100 to 200 bytes of data regarding date, time, floppy and hard disk drives, and much more. CMOS data can be divided in two groups: 

●   Data, which POST can not find during the system test.

●   Data, which contain user options. 

 For example, POST cannot by itself find sufficient information about the floppy drive(s). Floppy drives are so "dumb," that POST cannot read whether they are floppy drives or not, nor what type. About the same goes for IDE hard disks, while EIDE hard disks are a little more "intelligent," However, POST still needs assistance to identify them 100% correctly. The same goes for RAM: POST can count how much RAM is in the PC. However, POST cannot detect whether it is FPM, EDO or SD RAM. Since the CPU and BIOS reads data from RAM chips differently, depending on the RAM type, that type must be identified. 

Suppliers of system software 

All PC's have instructions in ROM chips on the system board. The ROM chips are supplied by specialty software manufacturers, who make BIOS chips. The primary suppliers are: 

●  Phoenix

●   AMI (American Megatrends)

●   Award

   You can read the name of your BIOS chip during start-up. You can also see the chip on the system board.

The Setup program 

You communicate with the BIOS programs and the CMOS memory through the so-called Setup program. Typically you reach the Setup program by pressing [Delete] immediately after you power up the PC. That brings you to a choice of setup menus. You leave Setup by pressing [Esc], and choose "Y" to restart the PC with the new settings. Generally, you should not change these settings, unless you know precisely what you are doing. The Setup program can do many things for you. You have to enter Setup, if you install a different type or additional disk drive in your PC. Certain BIOS's will also need adjustment of its settings, if a CD ROM drive is installed on one of the EIDE channels. 

Modifying the boot sequence 

You can change the boot sequence from A:, C: to C:, A:. That means, that the PC will not try to boot from any diskette in the A drive. That will protect you from certain virus attacks from the boot sector. Also, the boot process will not be blocked by any diskette in the A drive. If you need to boot from A-drive (for example, if you want to install Windows 97 ), you have to enter Set-up again, and change the boot sequence to A:, C:. That is no problem. 

Power Management

You also use the Setup program to regulate Power Management, which is the power saving features in the system board. For example, you can make the CPU shut down after one minute of no activity. There are plenty of settings available in this area. 

Password Protection 

You protect the Setup program with a password. This is used widely in schools, where they do not want the little nerds to make changes in the setup. Please remember the password (write it down in the mainboard manual). If you forget it you have to remove the battery from the mainboard. Then all user-input to the CMOS is erased - including the password.

The BIOS programs

During start-up. the BIOS programs are read from a ROM chip. BIOS is abbreviation of Basic Input Output System and those are programs, which are linked to specific hardware systems. For example, there is a BIOS routine, which identifies how the PC reads input from the keyboard. BIOS is a typical link in the IBM compatible PC design. The BIOS programs control hardware, the user (programmer) controls hardware via a call to BIOS. BIOS typically occupy 1 MB, and the programs are saved ROM chips on the system board. During start-up, BIOS is read from ROM chips. That information is supplemented with the system data saved in CMOS. Furthermore, there is BIOS code on the expansion cards. The expansion cards are external hardware, as interpreted by the system board, and the BIOS code, which is linked to the expansion card, must be included in the configuration. Therefore, this expansion card ROM is read during start-up, and the program code is woven together with other BIOS data. It is all written into RAM, where it is ready for the operating system,

BIOS-update 

BIOS programs can be updated. The modern system board has the BIOS instructions in flash-ROM, which can be updated. You can get new BIOS-software from your supplier or on the Internet, which can be read onto the system board. The loading is a special process, where you might need to change a jumper switch on the system board. Usually, you do not need to do this, but it is a nice available option.

ATX

The latest PC electronic standard is called ATX. It consists of a new type system board with a specific physical design smaller than the traditional board (30.5 cm X 19 cm). The I/O connectors COM1, COM2 and LPT, keyboard, mouse and USB are mounted directly on the system board. The ATX board requires specifically designed chassis's with an I/O access opening measuring 1¾ by 6¼ inch. ATX is designed by Intel, but has gained general acceptance. The ATX system board is more ”intelligent” than the ordinary type. In a few years, it will be wide spread. It includes advanced control facilities, where the BIOS program continually checks the CPU temperature and voltages, the cooling fans RPM, etc. If over heating occurs, the PC will shut down automatically. The PC can also be turned on by for example modem signals, since the power supply is controlled by the system board. The on/off button will turn the PC "down" without turning it completely off. If you want a PC designed for the future, the ATX layout is what you should go for.