Electronics Online

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

The PC construction
The PC consists of a central unit (referred to as the computer) and various peripherals. The computer is a box, which contains most of the working electronics. It is connected with cables to the peripherals.
On these pages, I will show you the computer and its components. Here is a picture of the computer (old computer):

The technical term for a PC is micro data processor. That name is no longer in common use. However, it places the PC in the bottom of the computer hierarchy:

• Mainframes are the very largest computers – million dollar machines, which can occupy more than one room, An example is IBM model 390.
• Minicomputers are large powerful machines. They typically serve a network of simple terminals. IBM’s AS/400 is an example of a minicomputer.
• Workstations are powerful user machines. They have the power to handle complex engineering applications. They use the UNIX or sometimes the NT operating system. Workstations can be equipped with powerful RISC processors like Digital Alpha or MIPS.
• PC’s are the Benjamin’s in this order: Small inexpensive, mass produced computers. They work on DOS, Windows, or similar operating systems. They are used for standard applications.

The point of this history is, that