SOFTWARE
INTERRUPTS:
The basic input/output system (BIOS) communicates directly with the hardware of the computer. It consists of set of programs, which interface with device such as keyboards, display, printer, serial port, Without BIOS the computer system will simply of bundle of wires and electronic device. There are two parts of BIOS the first part is permanently stored in non volatile memory called read only memory.(ROM)This parts starts the computer bootstrap. The second is loaded when the operating system is started.
An operating system allows the user to access the hardware in an easy to use manner. It accepts command from the keyboard and displays them to the monitor. The Disk operating system gained its name by from its original purpose of providing a controller for the computer to access its disk drive. The language of DOS consists of a set of command, which are entered directly by user and interpreted to perform file management task.
HARDWARE INTERRUPTS:
Computer systems either use poling or interrupt driven software to service external equipment. With poling the system continually monitors a status line and wait for it to become archive. An interrupt driven device sends an interrupt request to the computer, which is then serviced by Internet service routine
(ISR)
DISABLING INTERRUPT
HARDWARE SUPPORT:
A process runs until it invokes an operating system service or until it is interrupted. Here our attempt is to explain how to disabling interrupts. While one process is busy updating shared memory in its critical region, no other process will enter it critical region and cause trouble.
The simplest solution is to have each process disable all interrupts just after entering its critical region and re-enable them just before leaving it. With interrupts disenable, no clock interrupt can occur. The central processing unit is only switched from process to process as a result of clock or other interrupt. After all and with interrupt turned off, the CPU will not be switched to another process. Thus one process has disabled interrupts, it can then examine and update the shared memory before without fear that any other process will intervene. This approach is generally unattractive because it is unwise to give user processes the power to turn off interrupts. Also, if the computer has two or more CPUs disabling interrupts affect only the CPU that executed the disable instruction. The other ones will continue running and will continue running and access the shared memory.
On the other, it is frequently convenient for the kernel itself to disable interrupts for a few instructions while it is updating variable. If an interrupt occur while the list of ready processes is in an inconsistent state, race condition could occur. Thus disabling interrupt is sometimes a useful technique within the kernel.