BIOS Chipology

Remember An essential part of studying the BIOS is studying the chips (as in integrated circuits made from silicon "chips") on which it is stored and delivered to the PC.

l Read Only Memory (ROM): Although not solely a BIOS chip, ROM chips are permanently loaded with instructions during the manufacturing processes. The instructions written to a ROM chip, which cannot be changed under any circumstance, are called firmware. No longer a common vehicle for the system BIOS, on earlier PCs, the BIOS was stored on a ROM chip.

A ROM BIOS chip mounted on a PC motherboard.

l Programmable Read Only Memory (PROM): A PROM is essentially a blank ROM chip that can be programmed with data or instructions. A PROM burner (also called a PROM programmer), a special device used to write to the PROM, enables you to store any data you want. The PROM burner induces high voltage (12 volts compared to the 5 volts used for normal PROM operations) to load the data to the chip. The higher voltage burns a memory location to turn its preexisting binary 1 into a 0, if needed. This process is irreversible so what you burn is what you get (WYBIWYG). After you burn that zero into the PROM, there's no going back. For that reason, you may hear PROM memory referred to as One Time Programmable Memory.

l Erasable Programmable Read Only Memory (EPROM): An EPROM (pronounced "e-prom," which isn't a dance attended over the Internet) is a variation of the original PROM with the added feature of data that can be erased so that the chip can be reprogrammed. Unlike the PROM, you can reuse the EPROM instead of discarding it when its contents are no longer valid. The EPROM has a small quartz crystal window on the top of the chip through which ultraviolet (UV) rays can access the chip's circuitry. The UV light causes a chemical reaction that erases the EPROM by turning the 0's back into 1's again. To prevent accidental erasure of the EPROM chip, a label tape is normally placed over the quartz crystal window. Figure 5-3 shows an EPROM chip. The downside of an EPROM is that it must be removed from the system to be reprogrammed, which is not always possible.

An EPROM chip.

l Electronically Erasable Programmable Read Only Memory (EEPROM): An EEPROM (pronounced "e-e-prom") is the common BIOS chip on newer systems. An EEPROM chip can be reprogrammed like the EPROM, but unlike the EPROM it doesn't need to be removed from the motherboard. An EEPROM can be updated through specialized software that is usually downloaded from the BIOS or chip manufacturer's Web site. This process is known as flashing, which is why this chip is also commonly called flash ROM . Because they're easy to upgrade, EEPROM chips are also used in a variety of other things, such as cars, modems, cameras, and telephones.

Getting to Know the BIOS

The BIOS (Basic Input/Output System) is a collection of software utilities and programs that can be invoked by the operating system or application software to perform a variety of hardware-related tasks.

Although many operating systems now contain their own device-oriented programs to improve performance, the BIOS contains a program for just about every activity associated with accessing hardware, including programs for starting the system, testing the hardware, reading and writing to and from storage devices, and moving data between devices.

It boils down to this: The BIOS is the opening act of the PC. It ensures that the hardware is alive, well, and ready for the operating system and then gets the operating system up and running. If you're like most PC users, you probably give the system BIOS of your PC very little notice each time it does its magic when you power it up. That is, until there's a problem and then you'd probably like to shoot the messenger.

Remember The BIOS performs three primary functions, all vital to the usefulness and function of the computer:

l It boots the PC.

l It verifies the configuration data that tells it the internal and peripheral devices that are supposed to be connected to the PC.

l It provides the interface between the hardware (the attached devices) and the software (such as the operating system, device drivers, and application software).

Booting the PC

The instructions that start up the PC and load the operating system into memory and keep it running are part of the group of instructions that are collectively referred to as the system BIOS. The process of starting up the computer and loading the operating system is commonly called booting the computer, or simply the boot sequence. Booting and boot do not refer to any part of kicking or stomping, but are derivatives of the phrase "pulling oneself up by one's own bootstraps," or being able to self-start. When the computer boots, the BIOS is in charge.

When the PC is powered on, the BIOS supplies the PC with its first set of instructions. The instructions supplied by the BIOS are what the PC executes during its power on or boot up sequences until it is able to fetch and execute instructions on its own.

Verifying the hardware

The configuration of a PC is stored in a special type of nonvolatile memory, called Complementary Metal-Oxide Semiconductor, or CMOS (pronounced "sea-moss"), which requires very little power to hold onto its contents. CMOS is the technology used in nearly all memory and processor chips today.

However, in early PCs, it was used only to store the configuration data of the PC. So, although it's used throughout the PC's circuits, CMOS is synonymous with the storage of the PC's configuration data.

CMOS runs on about 1 millionth of an amp of electrical current. This efficiency allows it to store configuration data for a long time, perhaps even years, powered only from low voltage dry cell or lithium batteries. The CMOS battery is located on the motherboard; in older systems it's located in a battery pack attached to the sidewall of the system case.

Instant Answer When the system starts the boot sequence, the BIOS starts a program called the Power- On Self-Test, or POST, that verifies the data in the CMOS to the physical devices it can detect on the system. More on this later in the chapter in the "Running the POST process" section.

Getting input in and output out

After the PC is up and running, its peripheral devices communicate with the system through their device drivers. The system BIOS allows your old PC AT software to run on your Pentium III PC. The BIOS interacts with the hardware to carry out the actions demanded of it. After the PC is booted, the BIOS becomes part of a four-layer software operating environment that allows software to run on a variety of PC platforms without too much trouble. shows the four layers of the PC's operating environment.

The operating layers of a PC.

The application layer (for example, a word processing application) interacts with the operating system, such as Windows, to process its inputs and outputs. The operating system, which can't possibly be created to be exactly compatible with every configuration of PC, interacts with the BIOS, which in turn interacts with the PC's hardware. The BIOS allows the operating system and the application to be created for a general class of hardware because it's specifically created to work with certain types and configurations of hardware. The layers use a standard interface, supplied by the BIOS, to interact with the layer below (or above) it.

Motherboard Form Factors

Motherboard Form Factors

Software Tools -- The Domestic tools and The Foreign Tools

The domestic tools

Most of the items in this group of software diagnostic tools are usually included as a part of the operating system.

l BIOS POST: This effective diagnostic tool is built right into the PC and runs automatically every time the PC is powered on. If a serious hardware problem exists, most likely the POST finds it and reports it to you.

l POST card: (Not the kind Aunt Sally sends to you from Iowa and the other exotic places she visits.) This piece of hardware (an expansion card) is a dedicated circuit card that interprets the POST error codes written to address 80h. (The "h" means hexadecimal) A POST card saves you the trouble of counting beeps and decoding them.

l MSD.EXE: (also known as Microsoft Diagnostics): This DOS utility, which should probably be carried with you, creates and reports a brief inventory of your PC. This inventory is useful for seeing a system's configuration, including the BIOS, disks, memory, and system resource assignments, such as IRQs (interrupt requests) and I/O (input/output) addresses to LPT and serial ports. It was included with MS-DOS and Windows versions through Windows 95, but it is no longer distributed.

Tip MSD.EXE will run under Windows 95. Although it is on the Windows 95 release CD and can be copied to the system, it isn't included in a normal Windows 95 installation. Run MSD.EXE in DOS mode, not in a DOS window, under Windows 95.

l SCANDISK.EXE: This program, installed as a part of all Windows versions, checks and reports hard disk problems, including file system corruption and hard disk read errors. If a PC is not shut down properly, this utility will run automatically when the PC is next restarted.

l MEM.EXE: This DOS utility is distributed with Windows 9 x versions. It provides details about the memory configuration and usage on a PC.

l DEFRAG.EXE: This DOS and Windows utility rearrange data clusters on the disk to improve disk I/O efficiency.

l SYSEDIT.EXE: This Windows tool is used to view or edit INI, AUTOEXEC. BAT,

CONFIG.SYS, and other system files.

l Windows Device Manager: This tool is useful on Windows 9 x and 2000 systems for a problem caused by a resource conflict, IRQ, DMA channel, or I/O address. The Properties feature shows the device driver, resource settings, and much more for a specific hardware device.

The foreign tools

Three types of software tools can be used to help troubleshoot, diagnose, or repair PC problems:

l Anti-virus: Due to the increase in e-mail, Web, and other Internet access, PCs need immunity against computer viruses. A variety of anti-virus software packages are on the market. Having an anti-virus program available on a floppy disk can help you solve a customer problem caused by a virus before it spreads to other system users.

l Diagnostic and troubleshooting: A number of diagnostics packages are available, such as QAPlus (www.diagsoft.com), AMIDiag (www. megatrends.com), and those listed in "Loopback plugs" earlier in the chapter, that perform troubleshooting, system tune-ups, hardware diagnostics, and system status reporting. Often these packages include other features such as file encryption, file compression, undelete, and other file utilities.

l Uninstaller/Cleaning: The Windows environment uses the first-in-stays-here mode of file management. Windows programs leave behind more junk than NASA, which is why uninstall and file cleanup software are essential tools. Although you may never be called upon to clean up a customer's files, you may need to remove conflicting or out-of-date DLLs or the like. For an extensive list of this type of software, visit CNET's Windows File Cleanup Utilities page at http://winfiles.cnet.com/apps/98/file-cleanup.html.

Resistors, capacitors, transistors, and diodes

Resistors, capacitors, transistors, and diodes

These four electronic components are the building blocks on which virtually every electronic circuit in
the computer is built. Each plays a distinctly different and valuable role in a circuit, as I explain in the
following:

l A resistor acts like a funnel to slow down the flow of current in a circuit.

l A capacitor is like a storage bin to hold a charge. The PC has a few large capacitors that can
literally kill you if you make contact with them, such as the capacitors in the monitor and in the
power supply.

l A diode is a one-way valve that allows the current to flow in only one direction.

l A transistor is a semiconductor that stores one binary value.

l Transistors, resistors, capacitors, and diodes produce logic gates. Logic gates create circuits, and
circuits make up electronic systems.

Conductors, insulators, semiconductors

Conductors, insulators, semiconductors

A conductor , such as copper, carries an electrical current. An insulator , such as rubber, doesn't carry an electrical current, which is why a copper wire conductor is usually wrapped with a rubber insulator.

In the conducting electricity scheme of things, halfway between a conductor and an insulator is a
semiconductor . Although its name technically means "half-conductor," it's really neither a conductor
nor an insulator. When a semiconductor is zapped with electricity or light, it toggles to either a
conductor or an insulator, depending on what it was at the time it was zapped.

Common Electrical Measurements