ROM BIOS

ROM BIOS is a group of programs permanently stored on a ROM chip or chips on the systemboard that manages the most fundamental communications between software and hardware. The two functions of ROM BIOS are to:

1. Gather configuration information and initialize the computer when it is first turned on

2. Provide software to communicate directly with various hardware components when the OS is functioning

Configuring And Initializing The Computer

When you turn on the power to a PC, the CPU begins the process of initialization by turning to the ROM BIOS for instruction. The BIOS runs a series of complex programs called the Power-On Self Test (POST), which performs several tasks including the following:

· Testing the CPU itself

· Testing RAM

· Inventorying the hardware devices installed on the computer and comparing that inventory to configuration information

· Configuring disk drives, hard drives, keyboard, monitor and ports

· Configuring other devices installed on the PC, such as a CD-ROM or sound card

· Assigning resources to computer hardware devices in preparation for the OS to complete and coordinate these assignments

· Setting up hardware devices to go into "sleep mode" to conserve electricity

· Running CMOS setup if requested

· Loading into memory and turning control to the OS

Providing BIOS Services

ROM BIOS on the systemboard includes the BIOS startup program (see NP fig2) that is used only when the PC first boots. However, there are also portions of ROM BIOS programming that are stored in memory and used to support hardware devices when you run applications programs. Recall, this is sometimes called System BIOS.In NP fig2, System BIOS is labeled "BIOS on systemboard." For example, the keyboard is controlled by a BIOS program stored on the systemboard that is copied into memory by the ROM BIOS startup program. In this figure you see ROM BIOS playing two roles. First, the startup BIOS is in control, configuring the system, The keyboard BIOS is copied from the ROM BIOS chip on the systemboard into memory and is later used in its second role, to service the keyboard. The startup BIOS is no longer used after it turns control over to the OS, but other system BIOS programs continue to be used during computer operations.

While some if the system BIOS services are provided by the one or two ROM BIOIS chips on the systemboard, other system BIOS services are provided by chips on a supporting circuit board. This portion of system BIOS is called on-board BIOS. An example of on-board BIOS is the software on a video card. The BIOS on the video card is part of the total BIOS services for the entire system. When the computer is first turned on, the BIOS on the systemboard and the BIOS on the video card cooperate to provide part of the total BIOS services for the system. (Also, recall that rather than being controlled by BIOS programs, hardware is sometimes managed by device drivers, which are programs stored as files on the hard drive.)

When the CPU needs to display something on the monitor screen, it depends on the video BIOS to instruct the monitor. The CPU knows where to find the BIOS software for the monitor because its location is determined during the booting process. When you press a key on the keyboard, the CPU is told that the "keyboard needs attention" and also interprets the data from the keyboard. The BIOS programs to do all this are assigned memory addresses and are matched up with the correct peripheral device during the booting process. These programs are permanently stored on ROM BIOS chips on the systemboard and supporting circuit boards.

For example, sometimes a disk drive is controlled by a system BIOS program that is a part of ROM BIOS on the systemboard. During the booting process, startup BIOS assigns memory addresses to the system BIOS program that controls the disk drive. This program takes control and initializes the disk drive. During the operation of the PC, when an application must read from or write to disk, the request is passed to the OS which, in turn, passes the request to the system BIOS program that controls the disk drive.

Flash ROM

Flash ROM is a type of memory chip that permanently retains programming code without being electrically charged, but can also be overwritten by new code. With Flash ROM, you can upgrade ROM without having to install a new ROM BIOS chip, which is the more difficult and more expensive ROM update procedure. You can upgrade BIOS in Flash ROM by overwriting existing BIOS code with new BIOS code stored on disk or downloaded from the internet. As you add new devices to your system, you can continue to easily and inexpensively update ROM BIOS to manage these devices.

Technically speaking, Flash ROM is called EEPROM (electronically erasable programmable read-only memory), which means you can change the programming on the chip through software on your PC. The updated programming will be retained-even when you turn off your PC for long periods of time-until you change it again. Flash ROM allows you to upgrade system BIOS without having to replace the ROM chip.

As more devices become Plug-and-Play-compliant, Plug-and-Play BIOS will become more sophisticated. Expect to upgrade to Plug-and-Play BIOS over time. Additionally, makers of BIOS code are likely to change BIOS frequently because it is so easy for them to provide the upgrade on the Internet. You can get upgraded BIOS code from manufacturers' Web sites or disks from third-party BIOS resellers' Web sites or disks.

To upgrade Flash ROM, follow the directions that came with your systemboard and the upgrade software itself. Generally, you will perform these tasks:

· Set a jumper on the systemboard telling the BIOS what to expect

· Copy the upgrade software to a bootable disk

· Boot from the disk and follow the menu options to upgrade the BIOS

· Reset the jumper, reboot the system, and verify that all is working

*** Be very careful that you upgrade the BIOS with the correct upgrade. Upgrading with the wrong file could make your system BIOS totally useless. If you're not sure that you're using the correct upgrade, don't guess. Check with the technical support for your BIOS before moving forward. Before you call technical support, have the information that is written on the BIOS chip label available.

POST (Power On Self Test)

When you first turn on your computer, the CPU looks for instructions in the ROM BIOS Startup Program. The first process executed is POST, which first checks that the CPU is working. The CPU then sends signals over the system bus checking various chips, ports, and expansion slots. It then checks the system clock making sure timing is working properly. Because the CPU has not yet checked the video system, errors encountered up to this point are communicated to you by a beeping sound. Short and long beeps indicate an error. Next, POST checks the video controller card, sometimes called the display adapter. After the video controller passes inspection, POST can use the monitor to display its progress. POST then checks RAM by writing and reading data. A running count of RAM is displayed on the monitor during this phase.

Next, the keyboard is checked, and if you press any keys at this point, an error occurs. Secondary storage, including disk and hard drives, is checked. The hardware that POST finds is checked against the data stored in CMOS chips, jumpers, and/ or DIP switches to determine that they agree.

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