System software

Together, the operating system and the ROM BIOS program routines form the layer on which the user programs "rest." When the PC has to work, an operating system has to be read from a disk. There are many different operating systems to choose from. However, the BIOS is always placed firmly andcentrally in the PC hardware.

BIOS - firmware

One of the fundamental techniques in the PC design is the BIOS program layer. BIOS (Basic Input Output System) is a group of small programs, furnished by the PC manufacturer - also called firmware.

The BIOS routines are placed in the hardware - in a ROM chip - and are always available. Being stored in the hardware, they are functional regardless of which operating system they have to work with. So, in designing an operating system, one must pay close attention to the BIOS. The operating system must be able to work closely with the BIOS.

BIOS contains some very basic program routines, which handles data transfer between different hardware components. During PC start-up, the BIOS programs are the only accessible software. Later in the start-up process, the operating system is read,. It will then take control of the PC. The operating system has to provide a user interface, on which the use programs can rest. Thus, the operating system has two "faces": One pointing up towards the user and his/hers programs and one pointing down towards the system and hardware:



As computers have become more and more powerful, the user interface has become more graphic and user friendly. In a few years we will be able to address our commands directly to the operating system (you can do it already today with IBM's OS/2). Thus, the "upwards" face of the operating system will change greatly - supported by technological development. The "downwards" face - the operating systems interface with hardware - will change less. At least, the fundamental principles are the same as in the childhood of the PC.

BIOS or drive programs

The operating system must be able to communicate with hardware. As we are going to see, this can be done in two ways:

• The operating system communicates directly with hardware through drive programs.
• The operating system utilizes the BIOS programs.

While BIOS is hardware specific program code, stored in hardware, the drive programs are small hardware specific program elements read from the disk together with the operating system.
Depending on which operating system is installed, both principles are used in various degrees. Since the BIOS programs consist of 16 bit code, it is typically DOS (a 16 bit operating system) which utilizes BIOS to a large degree. In the newer 32 bit operating systems, it is not efficient to use BIOS any more than necessary.
Here is a model, which shows the operating system with BIOS and drive programs (usually just called drivers):



As you can see, the driver/BIOS functions are closely associated with the operating system. So let us
look at that: