ROM BIOS, Plug-and-Play BIOS, The CMOS Settings

ROM BIOS

There is one ROM chip on the systemboard that contains BIOS, which manages the startup process (startup BIOS) and many basic I/O functions of the system (system BIOS).

This one ROM BIOS chip on the systemboard contains only a portion of the total BIOS code needed to interface with all the hardware components in the system. Understanding that BIOS programs can come from several sources helps in solving memory problems and other problems that arise from resource conflicts.

The Total BIOS In Your System

Some expansion cards, such as a network interface card (NIC) or a video/graphics card, also have ROM chips on them containing BIOS code. The operating system uses the programs stored on these ROM chips to communicate with the peripheral devices.

During the boot process, the expansion card tells the startup program how many memory addresses that it requires to access its ROM code. For protected mode firmware, any memory addresses will do, but, for older legacy cards using real mode, the BIOS must be assigned addresses in base memory or the upper memory area between 640K and 1024K. The ROM code from these boards becomes part of the total BIOS that the operating system uses to communicate with peripherals. Problems referred to as hardware configuration conflicts can occur if two legacy boards request the same addresses in upper memory.

Plug-and-Play BIOS

Plug-and-Play (PnP) is a term that applies to both the Windows 9x operating system and to some ROM BIOS. It means that rather than having you reset DIP switches and jumpers, the operating system and/or the BIOS automatically configures hardware devices to reduce or eliminate conflicting requests for such system resources as I/O addresses, IRQs, DMA channels, or upper memory addresses. Windows 9x Plug-and-Play assigns these resources to a device only if the device allows it. For example, if a legacy sound card requires a certain group of upper memory addresses that are hard coded into its on-board BIOS, there’s nothing that Windows 9x Plug-and-Play can do about that. (Hard coded is computer jargon for something being coded so that it cannot be changed.) Plug-and-Play simply tries to work around the problem as best it can. If two non-Plug-and-Play hardware devices require the same resource and their BIOS does not provide for accepting a substitute, these two devices cannot coexist on the same PC.

The CMOS Settings

System-board manuals should contain a list of all CMOS settings, an explanation of their meanings, and their recommended values. When you purchase a systemboard or a computer, be sure the manual is included for this purpose.

If you don’t have the manual, you can sometimes go to the system-board manufacturer’s Web site and download the information you need to understand the specific CMOS settings of your computer.