BIOS and Memory
BIOS Configuration
Objectives:
To discuss BIOS configuration, physical memory, and interrupt request handling
Explain the function of the BIOS
Describe how the BIOS settings are stored
Outline the most common BIOS settings in a PC
Discuss the main types of memory in a PC
Describe how to install a physical memory module on a PC
Describe how interrupt requests work
Outline the most common usage for the various interrupt request lines in a PC
Lesson:
BIOS stands for basic input/output system.
The system BIOS is the lowest level software in the computer, and it is actually built into the PC's hardware.
It is also the most important BIOS in a PC and is located in a 64KB block of memory from F0000h to FFFFFh.
The system BIOS acts as an interface between the system hardware - particularly the chipset and the processor - and the operating system.
The system BIOS ensures that an operating system - such as Windows 98 or Windows
2000 - can run on any type of PC without alteration.The system BIOS is also responsible for allowing a user to control hardware settings, such as the boot up sequence when the power is turned on or the reset button is pressed.
The BIOS settings that are used to control how a PC works must be saved in nonvolatile memory so that they are preserved even when the machine is powered off.
This memory is different from regular system memory, which is cleared each time a PC is turned off.
The main hardware component of the system BIOS is the system BIOS ROM itself.
This is normally located in an electrically-erasable programmable read-only memory (EEPROM) chip, which allows it to be updated using software.
This is commonly known as a Flash BIOS.
Flash memory is memory that can be erased and reprogrammed in blocks instead of one byte at a time.
Other BIOS settings were held in CMOS ROM.
CMOS stands for complementary metal-oxide semiconductor.
It is a type of technology used to make semiconductors such as processors or chipsets.
Compared to other semiconductor technologies, CMOS requires very little power - this is why it is ideal for storing BIOS settings.
It does not place excessive demands on the battery, and so the battery can last for a very long time.
Flash BIOS, on the other hand, does not require power to keep settings refreshed.
BIOS memory is sometimes referred to as NVRAM - nonvolatile RAM.
The BIOS ROM can be located in a socket on the motherboard and is generally labeled with the name of a BIOS manufacturer - Award, American Megatrends (AMI), or Phoenix, for example.
Flash BIOS is normally surface-mounted on modern motherboards.
The BIOS is best known for the BIOS setup program, which allows the user to control
how the PC works.The BIOS setup program allows you to set various parameters in your PC.
Some BIOS settings are quite universal, while others are specific to those made by a particular manufacturer.
Every motherboard should have instructions with it on how to use the BIOS setup program.
Often, the most up-to-date instructions are available on the Internet.
There is no standard interface for the BIOS setup program - the interface depends on the BIOS manufacturer.
Some are Windows-like, while others are text- and menu-based.
Before any BIOS settings are adjusted, it is important that a record is made of the original settings in case of problems.
The BIOS setup program can normally be entered only during the boot process, although some setup programs will let you access them at any time using a key combination.
In general, the Delete key provides access to the setup program during the boot process.
Other BIOSes can use many different key combinations, including
• Esc
• F1
• F2
• Ctrl+Esc
• Alt+Esc
• Ctrl+Alt+Esc
The motherboard manual will contain the information needed to enter the setup program.
Once the setup program has been accessed, the various BIOS setting options are visible and can be adjusted if required.
There are standard settings available with almost all BIOSes, and there are also more advanced settings which are BIOS-specific.
Let's now take a look at some of the standard settings.
The system date setting is a standard one and must be set correctly.
In North America, the format is usually mm/dd/yyyy, but this can vary in different
parts of the world.The system time setting is generally entered using a 24-hour clock.
If a BIOS has a daylight savings setting, it will advance the time by one hour on the first Sunday in April and drop it back by one hour on the last Sunday in October.
The default value is usually "Enabled".
The IDE primary master setting is where the hard disk parameters are entered for the first IDE drive.
And the IDE primary slave setting is where the hard disk parameters for the second IDE drive are entered.
The IDE secondary master setting is where the hard disk parameters are set for the secondary master IDE device, which is usually the third drive in a modern IDE system.
However, it can be the second drive if a primary slave device is not used.
The parameters for the fourth drive in an IDE system are entered in the IDE secondary slave setting area.
In the case of a system with IDE autodetection, the default for all IDE drives is "Auto".
The setting for the type of the first floppy drive must be entered.
These are the choices available:
• 1.44/1.25MB - a normal 3.5"drive
• 1.2MB - a normal 5.25" drive
• 2.88MB - a high density 3.5"drive
• 720KB - a low density 3.5"drive
• 360KB - a low density 5.25"drive
The setting for the first floppy drive usually defaults to a 1.44MB 3.5" drive, which is the most common type currently in use.
The settings for a second floppy drive must also be entered, and the choices are the same as those for the first floppy drive.
As well as basic BIOS settings there are more advanced settings that give you extra control over the behavior of a PC system.
The Cache Size (L1/L2) setting shows how much L1 and L2 cache is installed.
There are many advanced BIOS settings available on some PCs.
However, unless the user is particularly familiar with BIOS settings, it is generally recommended that the default settings are used.
In specific areas of the BIOS setup program - hard disk autodetection, for example - automatic configuration options are offered.
In addition to this, most BIOSes also offer a menu selection to automatically set all options in the BIOS to predefined settings.
Autoconfiguration selections do not generally replace the settings in the standard section of the BIOS - floppy types, for example.
So, in many cases this is the safest option for configuring the BIOS.
Sometimes the BIOS in a PC may need to be upgraded.
With older PCs this sometimes meant replacing the ROM BIOS chips on the motherboard.
PCs with Flash BIOS, however, can have their BIOS upgraded using a simple software routine.
The new BIOS can be downloaded from the Internet, or may arrive on disk.
Upgrading a Flash BIOS is usually performed by preparing a boot floppy with the Flash upgrade on it and rebooting the PC for the new BIOS to be installed.
With some motherboards you may need to change jumper settings in order to upgrade the BIOS.
Do not interrupt the BIOS update process, doing so could render your system not functional.