Difference between BIOS and dos functions?

Answer 1

What is the difference between BIOS and DOS routines? how many types of interrupts?

Different Answer

BIOS stands for Basic Input/Output System, while DOS stands for Disk Operating System. BIOS is considered "Firmware" because it retains the bit data within it after the machines power is turned off (EEPROM). The BIOS is the sub-layer of machine code that allows an AT style computer to start running. When you have a PC in front of you with its power off, what you have is all the hardware in one place in a configuration necessary to allow a (Powerful) digital computer to come to life in front of you. Let's imagine we've removed the BIOS chip. Now let's apply power. The computer would sit there doing nothing. Even though DOS (or Windows XX) may be installed on some external storage device, the hardware has no way of knowing this.

The CPU hardware is designed to force the first instruction it executes to be a Jump through memory location zero (Indirect Addressing). At location zero is supposed to be the address of the first external instruction to be executed. Without the BIOS chip installed, there is no instruction location address for the computer to start executing, so the machine would fail to start. To the computer, there is no software found in the machine. Without software, hardware is useless... without hardware, software is useless.

Let's power off, re-install BIOS, and turn power on. Now the general sequence of events is something like this;

· Jump through location zero to start running a program found at that address.

· Find out what basic hardware is present on the buses.

· Do a preliminary hardware check of these devices to determine if they are working.

· Stack a series of driver programs in memory that service the interrupts for these devices.

· Go to the BIOS defined external device to find an Operating System (OS).

· Load the found OS's boot program into memory.

· Turn control of the computer over to the OS boot program.

· The boot program loads memory with the OS executive loop and turns control over to it.

· The executive loop finishes loading installed software interfaces

· The OS then presents itself to the user for command.

Depending on what OS is installed; you'll eventually see the User Interface that allows you to command the OS through the human designed I/O devices recognized by the computer during boot (Keyboard, Monitor, etc).

The OS is running in a loop that services hardware interrupts as they come in. When you press a key on your keyboard, the special purpose computer in the keyboard sends a hardware interrupt telling the computer there is something coming in that needs attention. The operating system gives the driver associated with that device time on the CPU. That driver uses the BIOS to reach out to the device and accept what it needs to send. What the device sends is loaded into a buffer in RAM that becomes available to the OS and is then manipulated in whatever way the OS is programmed to interpret that data.

So, BIOS is the low level interface software running on your machine. The OS (like DOS) is higher level software running on the machine that uses BIOS to interface with the hardware, which you are using to control the OS.