On completion of this tutorial, you will be able to:
- Define the function of BIOS
- Define the terms EEPROM and EPROM
- Describe the features of Flash BIOS
- Name two reasons why you might upgrade BIOS
The Function of BIOS
Starting the System
Operating systems (for example, Windows 98 and Windows 2000) and applications (for example, Word and Excel) are made up of instructions that are loaded into system RAM from the local hard disk drive or network drive. When the PC is turned on, the system RAM is "empty" and there are no instructions available to tell the processor how to start these programs.
Therefore, when you turn the PC on, BIOS instructions are loaded into RAM from a permanently available ROM chip on the motherboard. These instructions inform the processor where the operating system is located and how to load it into RAM. Once the operating system is loaded, you can use it to start your applications.
A standard created by processor manufacturers ensures that the processor always looks in the same place for the start of the BIOS program. The instructions are loaded into the last 64K of the first megabyte of system memory (F0000-FFFFF in hexadecimal). Some BIOS\'s use more than this 64K area.
Hardware Independence
In order to allow operating systems and applications to run on a PC, (almost irrespective of its age), the BIOS (Basic Input Output System) provides a standard layer of services that the operating system can use to "talk" to the hardware. In turn, the operating system provides standard services to applications to perform their functions.
This means that one layer has to know how to communicate with the layer above (or below) only. This "layering" of services allows applications to run on virtually any PC regardless of the type of hardware.
BIOS Services
The services provided by BIOS include, for example, disk I/O and power management. Not all operating systems use these services; some use their own instructions to access the hardware. This method of accessing the hardware may improve performance.
Some specific examples of BIOS services are:
- Geometry Translation for IDE/ATA Hard Drives Over 504 MB
- Plug-and-Play
- Year 2000 Compliance
- Support for IDE/ATA Hard Drives Over 2 GB
BIOS Components
The BIOS ROM Chip
Most older BIOS ROMs are supplied in the form of Erasable Programmable ROMs (EPROMs). The BIOS manufacturer can use a programming device to fill these chips with information. Once written, this data is stored semi-permanently (for about 10-15 years).
EPROMs are cheap to purchase and can be mass-programmed using large gang-programmers. Most importantly, you can erase an EPROM by shining strong ultraviolet light through a clear quartz glass (UV-transparent) window on the top of the chip. This is ideal for development work as it allows old EPROMs to be erased and re-used.
Do not remove the sticker placed over the window of the EPROM. It is possible (but unlikely) that direct sunlight through a window may begin to erase the EPROM contents. For similar reasons, do not store programmed EPROMs in direct sunlight or near strong UV sources.
BIOS Upgrades
Motherboard manufacturers may regularly update their BIOS in order to fix bugs, solve incompatibilities with operating systems or to add new features. You should visit your motherboard manufacturer\'s Web site regularly to check if and when upgrades are available.
How to Upgrade
Although EPROMs are re-programmable using special equipment, re-programming is beyond the scope of most businesses. BIOS upgrades are generally shipped to customers using an old-for-new EPROM exchange program.
You must remove the old BIOS chip with the proper DIP chip removal tool. You must also insert the new chip with the correct tool. You should ensure that the semi-circular notch at one end of the chip matches up with a similar marking on the chip socket.
Flash ROM, or Electrically Erasable Programmable ROM (EEPROM), can be erased in place. Most motherboard manufacturers have switched to this form of ROM for holding the BIOS code.
Upgrade programs can be supplied by motherboard manufacturers on a floppy disk or downloaded from a Web site. As a security feature, a jumper on the motherboard usually has to be adjusted in order to allow BIOS upgrades to take place.
You cannot reuse EEPROMs indefinitely; some types have a lifetime of fewer than 100 reprogramming cycles. You should avoid unnecessary updating.
BIOS CMOS Memory and Battery
CMOS (Complimentary Metal Oxide Semiconductor) RAM is a small amount of volatile memory in a special RAM chip that stores the real time clock settings and configuration information for a PC. Plug-and-Play BIOS uses additional non-volatile memory to hold Extended System Configuration Data (ESCD). This is used to store system resource settings of system devices such as IRQs and I/O addresses.
Memory content is maintained with power from a small battery when the system is powered down. The battery may be any of the following:
- Alkaline cells attached to the motherboard with wires and velcroed to the power supply or system case
- A NiCad (Nickel-Cadmium) battery soldered to the board that looks like a small cylinder or barrel.
- A lithium cell in a metal holder, similar in appearance to a calculator or watch battery.
- A lithium cell or rechargeable NiCad battery integrated with the real-time clock chip and sometimes called a "Dallas real time clock".
Summary
In this tutorial you have learnt:
- The difference between an EPROM and an EEPROM chip
- About the function of BIOS
- How and when to upgrade BIOS
- About different types of CMOS battery
- About the parameters stored in CMOS
