BIOS is an acronym for Basic Input/Output System. It is the boot firmware program on a PC, and controls the computer from the time you start it up until the operating system takes over. When you turn on a PC, the BIOS first conducts a basic hardware check, called a Power-On Self Test (POST), to determine whether all of the attachments are present and working. Then it loads the operating system into your computer's random access memory, or RAM.
The BIOS also manages data flow between the computer's operating system and attached devices such as the hard disk, video card, keyboard, mouse, and printer.
The BIOS stores the date, the time, and your system configuration information in a battery-powered, non-volatile memory chip, called a CMOS (Complementary Metal Oxide Semiconductor) after its manufacturing process.
Although the BIOS is standardized and should rarely require updating, some older BIOS chips may not accommodate new hardware devices. Before the early 1990s, you couldn't update the BIOS without removing and replacing its ROM chip. Contemporary BIOS resides on memory chips such as flash chips or EEPROM (Electrically Erasable Programmable Read-Only Memory), so that you can update the BIOS yourself if necessary.
In batched operating system the users gives their jobs to the operator who sorts the programs according to their requirements and executes them. This is time consuming but makes the CPU busy all the time.
A multi-programmed operating systems can execute a number of programs concurrently. The operating system fetches a group of programs from the job-pool in the secondary storage which contains all the programs to be executed, and places them in the main memory. This process is called job scheduling. Then it chooses a
program from the ready queue and gives them to CPU to execute. When a executing program needs some I/O operation then the operating system fetches another program and hands it to the CPU for execution, thus keeping the CPU busy all the time.
It is a logical extension of the multi-programmed OS where user can interact with the program. The CPU executes multiple jobs by switching among them, but the switches occur so frequently that the user feels as if the operating system is running only his program.
They contain a no. of processors to increase the speed of execution, and reliability, and economy. They are of two types:
1. Symmetric multiprocessing
2. Asymmetric multiprocessing
In Symmetric multi processing each processor run an identical copy of the OS, and these copies communicate with each other as and when needed.But in Asymmetric multiprocessing each processor is assigned a specific task.