System Configuration Chapter 3

Objectives Distinguish between the various methods used to configure a computer Describe how to replace a motherboard battery Identify system resources such as interrupts, DMA channels, memory addresses, and I/O addresses

Configuration Overview The BIOS (basic input/output system) is an important motherboard component. The BIOS has the following functions: ▫Holds and executes POST (power on self test)— the program that identifies, tests, and initializes basic hardware components ▫Holds a basic routine called a bootstrap program that locates an operating system and allows it to load ▫Holds Setup, which is a program that allows device settings to be viewed and managed

The Setup Program Most computers have Setup software built into the system BIOS chip on the motherboard and accessed by specific keystrokes determined by the BIOS manufacturer. During the boot process, most computers will display a message stating which keystrokes will launch the Setup program. The keystroke can be one key pressed during startup such as the F1, F2 or Del keys.

Flash BIOS Flash BIOS is the most common type of BIOS that allows changing the BIOS without installing a new chip or chips. The following procedure is one example of “flashing the BIOS”: ▫Once the system BIOS upgrade is downloaded from the Internet, execute the update. ▫Follow the directions on the screen or from the manufacturer. ▫Reboot the computer.

CMOS Memory Settings changed in system BIOS are recorded and stored in CMOS (complementary metal oxide semiconductor) found in the motherboard chipset (south bridge or I/O controller hub). CMOS is low-powered memory powered by a small coin-sized lithium battery when the system is powered off.

BIOS Configuration Settings BIOS options vary according to manufacturer, but many options are similar. Table 3.1 shows some common BIOS settings and a brief explanation of each.

Motherboard Batteries The most common battery used today is a lithium battery about the size of a nickel. Figure 3.2 shows a photo of a lithium battery installed on a motherboard.

Plug and Play Plug and play (PnP) allows automatic software configuration of an adapter. A PnP adapter plugs into an expansion slot without having to configure the board or worry about the adapter conflicting with other adapters already installed in the system.

Configuration through Switches A switch (sometimes called a DIP switch) can be used to configure motherboard and adapter options. Switches can be found on older adapters and still can be found on motherboards and devices. There are two basic models of switches: slide and rocker.

Other Configuration Parameters Other possible parameters contained and set via the Setup program or operating system are ▫IRQs (interrupt requests), ▫I/O (input/output) addresses, ▫DMA (direct memory access) channels, and ▫memory addresses.

IRQ (Interrupt Request) The processor prioritizes device requests through the use of IRQ. An IRQ (interrupt request) is a number assigned to expansion adapters or ports so orderly communication can occur between the device or port and the processor.

I/O (Input/Output) Addresses An I/O address, otherwise known as an input/output address or port address, allows the device and the processor to exchange data. The I/O address is like a mailbox number; it must be unique or the mailman gets confused. ▫The device places data (mail) in the box for the CPU to pick up. ▫The processor delivers the data to the appropriate device through the same I/O address (mailbox number)

Table 3.7 shows common I/O addresses used in computers.

DMA Channels A DMA channel (direct memory access channel) is a number assigned to an adapter. The DMA assignment allows the adapter to bypass the CPU and communicate directly with RAM. Transferring the data directly to memory speeds up transfers. Devices that frequently take advantage of DMA are drives, tape backup units, and multimedia adapters such as sound cards. A drawback to DMA transfers is that the processor may be put on hold until the DMA data transfer is complete.

Memory Addresses A memory address is a unique address assigned to the BIOS, any other ROM chips installed on adapters, and RAM chips installed in the system. The memory address is used by the CPU when it accesses information inside the chip.

Configuration Overview ISA, EISA, PCI, PCIe, and AGP adapters must be configured for the proper IRQ, I/O address, memory address, and DMA channel. The system BIOS plays an important role when the computer boots. The BIOS detects installed adapters and, together with the operating system, determines what resources to assign to the adapter. ▫This information is stored in a part of CMOS known as the ESCD (extended system configuration data) area.

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