BIOS Hardware and Software

written by: Melinda Mirovich; article published: year 2006, month 09;



In: Categories » Computers and technology » Software » BIOS Hardware and Software

The BIOS itself is software running in memory that consists of all the various drivers that interface the hardware to the operating system. The BIOS is unique compared to normal software in that it doesn't all load from disk; some of it is preloaded into memory chips (read-only memory, or ROM) installed in the system or on adapter cards.

The BIOS in a PC comes from three possible sources:

  • Motherboard ROM

  • Adapter card ROM (such as that found on a video card)

  • Loaded into RAM from disk (device drivers)

The motherboard ROM BIOS is most often associated with hardware rather than software. This is because the BIOS on the motherboard is contained in a ROM chip on the board, which contains the initial software drivers needed to get the system running. Years ago, when only DOS was running on basic PCs, this was enough, so no other drivers were neededthe motherboard BIOS had everything that was necessary. The motherboard BIOS usually includes drivers for all the basic system components, including the keyboard, floppy drive, hard drive, serial and parallel ports, and more. As systems became more complex, new hardware was added for which no motherboard BIOS drivers existed. These included devices such as newer video adapters, CD-ROM drives, SCSI hard disks, USB ports, and so on.

Rather than requiring a new motherboard BIOS that would specifically support the new devices, it was far simpler and more practical to copy any new drivers that were necessary onto the system hard disk and configure the operating system to load them at boot time. This is how most CD-ROM drives, sound cards, scanners, printers, PC Card (PCMCIA) devices, and so on are supported. Because these devices don't need to be active during boot time, the system can boot up from the hard disk and wait to load the drivers during the initial operating system load.

Some drivers, however, must be active during boot time. For example, how could you boot from a hard disk if the drivers necessary to make the disk interface work must be loaded from that disk? Obviously, the hard disk drivers must be preloaded into ROM either on the motherboard or on an adapter card.

How will you be able to see anything onscreen if your video card doesn't have a set of drivers in a ROM? The solution to this could be to provide a motherboard ROM with the appropriate video drivers built in; however, this is impractical because of the variety of video cards, each needing its own drivers. You would end up with hundreds of different motherboard ROMs, depending on which video card you had. Instead, when IBM designed the original PC, it created a better solution. It designed the PC's motherboard ROM to scan the slots looking for adapter cards with ROMs on them. If a card was found with a ROM on it, the ROM was executed during the initial system startup phase, before the system began loading the operating system from the hard disk.

By putting the ROM-based drivers right on the card, you didn't have to change your motherboard ROM to have built-in support for new devices, especially those that needed to be active during boot time. A few cards (adapter boards) almost always have a ROM onboard, including the following:

  • Video cards. All have an onboard BIOS.

  • SCSI adapters. Those that support booting from SCSI hard drives or CD-ROMs have an onboard BIOS. Note that, in most cases, the SCSI BIOS does not support any SCSI devices other than a hard disk; if you use a SCSI CD-ROM, scanner, Zip drive, and so on, you still need to load the appropriate drivers for those devices from your hard disk. Most newer SCSI adapters support booting from a SCSI CD-ROM, but CD-ROM drivers are still necessary to access the CD-ROM when booting from another drive or device.

  • Network cards. Those that support booting directly from a file server have what is usually called a boot ROM or IPL (initial program load) ROM onboard. This enables PCs to be configured on a LAN as diskless workstationsalso called Net PCs, NCs (network computers), thin clients, or even smart terminals.

  • ATA or floppy upgrade boards. Boards that enable you to attach more or different types of drives than what is typically supported by the motherboard alone. These cards require an onboard BIOS to enable these drives to be bootable.

  • Y2K boards. Boards that incorporate BIOS fixes to update the century byte in the CMOS RAM. These boards have a small driver contained in a BIOS, which monitors the year byte for a change from 99 to 00. When this is detected, the driver updates the century byte from 19 to 20, correcting a flaw in some older motherboard ROM BIOS. Although it might seem strange to list Y2K boards because the century changed several years ago, if installed these boards often remain in use until the systems using them are retired.

BIOS and CMOS RAM

Some people confuse BIOS with the CMOS RAM in a system. This confusion is aided by the fact that the Setup program in the BIOS is used to set and store the configuration settings in the CMOS RAM. They are, in fact, two totally separate components.

The BIOS on the motherboard is stored in a fixed ROM chip. Also on the motherboard is a chip called the RTC/NVRAM chip, which stands for real-time clock/nonvolatile memory. This is where the BIOS Setup information is stored, and it is actually a digital clock chip with a few extra bytes of memory thrown in. It is usually called the CMOS chip because it is made using CMOS (complementary metal-oxide semiconductor) technology.

The first example of this ever used in a PC was the Motorola MC146818 chip, which had 64 bytes of storage, of which 14 bytes were dedicated to the clock function, leaving 50 bytes to store BIOS Setup settings. Although it is called nonvolatile, it is actually volatile, meaning that without power, the time/date settings and the data in the RAM portion will in fact be erased. It is considered nonvolatile by many because it is designed using CMOS technology, which results in a chip that still requires power but very little compared to other chips. A battery in the system, rather than the AC wall current, provides that power. This is also why most people call this chip the CMOS RAM chip; although not technically accurate (almost all modern chips use a form of CMOS technology), the term has stuck. Most RTC/NVRAM chips run on as little as 1 micro amp (millionth of an amp), so they use very little battery power to run. Most lithium coin cell batteries can last up to 5 years or more before the battery runs out and the information stored (as well as the date and time) is lost. Some systems use special versions of these chips made by Dallas Semiconductor, Benchmarq, or Odin (such as the DS12885 and DS12887) that include both the RTC/NVRAM chip and the battery in a single component.

When you enter your BIOS Setup, configure your hard disk parameters or other BIOS Setup settings, and save them, these settings are written to the storage area in the RTC/NVRAM (otherwise called CMOS RAM) chip. Every time your system boots up, it reads the parameters stored in the CMOS RAM chip to determine how the system should be configured. A relationship exists between the BIOS and CMOS RAM, but they are two distinctly different parts of the system.

legal disclaimer

1) Our website is not responsible for the information contained by this article as well for any and all copyright infringements by authors and writers. E-articles is a free information resource. If you suspect this article for any copyright infringements, please read the Terms of service and contact us to investigate the problem.
2) The E-articles directory team is not responsible for inaccuracies, falsehoods, or any other types of misinformation this tutorial may contain and will not be liable for any loss or damage suffered by a user through the user's reliance on the information gained here. Please read the Terms of service

Useful tools and features

Translate this article to...    Send this article to you or to a friend

Link to this article from your page   
If you like this article (tutorial), please link to it from your web page using the information above. Linking to this page, this is the only way to help us improve our service, the same time providing your visitors with a way to improve their online experience.

related articles

1. Remote Access Services (RAS) under Windows XP Professional
Authentication protocols • EAP - Extensible Authentication Protocol. A set of APIs in Windows for developing new security protocols as needed to accommodate new technologies. MD5-CHAP and EAP-TLS are two examples of EAP. • EAP-TLS - Transport Level Security. Primarily used for digital certificates and smart cards. • MD5-CHAP - Message Digest 5 Challenge Handshake Authentication Protocol. Encrypts usernames and passwords with an MD5 algorithm. • RADIUS - Remote...

2. Maximizing Your Internet Browser with Bookmarks
If you want to return to a first-rate online source, you’re likely to use a shortcut, such as a bookmark or a favorite. If you use the Netscape browser, you bookmark the Web page. This acts as a shortcut to the online source.If you use the Internet Explorer browser, you save the page as a favorite. (I refer to both of these types of shortcuts as bookmarks for this section of the article.) If you’ve used the Internet for a while, you likely have a long list of bookmarks. Today h...

3. Monitoring and Optimizing System Performance and Reliability in Windows XP Professional
Task scheduler: • Used to automate events such as batch files, scripts and system backups. • Tasks are stored in the Scheduled Tasks folder in Control Panel. • Running task with a user name and password allows an account with therequired rights to perform the task instead of an administrative account. • Set security for a task by group or user. Using offline files • Offline files replaces My Briefcase and works a lot like Offl...

4. Computer Tips and Tricks ~ How Do I Send Pictures via Email
One of the first things that new digital camera owners love to do is send a batch of images to family members or friends. As you may have already discovered yourself, the warmth of reception is inversely proportional to the size of the images that land in your recipients' inboxes. All too often, budding photographers send full-sized 2-, 4-, or even 6-megapixel pictures as email attachments. Unfortunately, these files take forever to download on all but the fastest Internet connections and are too large to view comfortably on a c...

5. Communication Protocols Used by Windows Systems
TCP/IP protocol • TCP is an industry-standard suite of protocols • It is routable and works over most network topologies • It is the protocol that forms the foundation of the Internet • It is Installed by default in Windows XP • Can be used to connect dissimilar systems • Uses Microsoft Windows Sockets interface (Winsock) • IP addresses can be entered manually or be provided automatically by a DHCP server • DNS is used to resolve compute...

6. Advantages and Disadvantages of FAT and NTFS File Systems
Understanding FAT and NTFS File Systems • NTFS provides optimum security and reliability through its ability to lock down individual files and folders on a user-by-user basis. Advanced features such as disk compression, disk quotas and encryption make it the file system recommended by 9 out of 10 MCSEs. • FAT and FAT32 are only used for dual-booting between Windows XP and another operating system (like DOS 6.22, Win 3.1 or Win 95/98). • Existing NT 4.0 NTFS system partit...

7. Two Software Nags ~ Windows 95 versus Windows NT
The buildup to NT began after the incredibly successful launch of Windows 3.0 in 1990. For the next 3 years, Microsoft spent considerable time proclaiming that this new version of the product, once known as OS/2 3.0, would be the 32-bit successor to the 16-bit Windows 3.x product line. But as NT neared completion, complaints began to surface that the product was too big and resource-hungry to fit the existing desktop profile. Microsoft had heard these complaints before with other products, but Moore's Law which, roug...

8. Investing ~ Portfolio management software programs
Several hundred portfolio management programs are available for your investment tracking. The programs vary in price from free to $800. Many of the freeware and shareware portfolio management programs include an amazing amount of features, but are somewhat cumbersome to use. Some brokers give free portfolio management programs to customers who open an account. Financial data providers frequently give free portfolio man agement programs with a subscription to their services. Other portfolio management programs are components of...