What happens when the Computer is switched on?

Power On Self Test (POST): when the computer is turned on, electricity flows through the power supply to the ROM-BIOS chip ( Read only Memory Basic Output System). The chips contain the permanent startup instructions for the computer and other instructions to tell the computer how to manage the input from the keyboard and the mouse and relay the output to the monitor and printer. The ROM BIOS instructs the computer to check that everything is connected and working properly. The CPU compares the POST information within the CMOS chip (Complimentary Metal Oxide Semiconductor). The CMOS is battery operated memory that keeps track of the time and date and knows how many disk drives you have and other useful information. If it matches the BIOS tells the CPU to load the operating system MS DOS. Otherwise an error message will appear on the screen. After the POST, the operating system instructions are read from the hard disk into the computer’s memory. If there is no operating system, there is no computer. The operating system works behind the scene to manage the computer’s operations. Once the operating system is loaded you can run other programs (applications). You can word process, create databases and spreadsheets, run other applications or play games. As you type, the computer saves the data in its memory, RAM (Random Access Memory), which requires a constant flow of electricity. You must save data from memory to disk (floppy or hard disk) to keep a permanent copy. Once you exit an application or lose electricity then the memory is lost. Some applications allow you to recover data but very few are present. Once you have saved your work to disk you can retrieve your data from disk (floppy or hard disk) into memory till when it is required. As stated earlier, when the computer is switched off, it forgets everything. The computer memory only works when it receives electricity. For this reason, information from the memory can be saved and stored on devices notably diskettes. Therefore the computer can: • Save or store the contents of the memory on diskettes • Get information from the diskettes and load into the computer’s memory.