CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [108]
The TPM can be a small circuit board plugged into the motherboard, or it can be built directly into the chipset. The CMOS setup program usually contains settings that can turn the TPM on or off and enable or disable it.
TPMs can be used in a wide array of cryptographic operations, but one of the most common uses of TPMs is hard disk encryption. For example, the BitLocker Drive Encryption feature of Microsoft’s Windows Vista can be accelerated by a TPM, which is more secure because the encryption key is stored in the tamper-resistant TPM hardware rather than on an external flash drive. Other possible uses of TPMs include digital rights management (DRM), network access control, application execution control, and password protection.
Exiting and Saving Settings
Of course, all CMOS setups provide some method to Save and Exit or to Exit Without Saving. Use these as needed for your situation. Exit Without Saving is particularly nice for those folks who want to poke around the CMOS setup utility, but don’t want to mess anything up. Use it!
The CMOS setup utility would meet all of the needs of a modern system for BIOS if manufacturers would just stop creating new devices. That’s not going to happen, of course, so let’s turn now to devices that need to have BIOS loaded from elsewhere.
Option ROM and Device Drivers
Every piece of hardware in your computer needs some kind of programming that tells the CPU how to talk to that device. When IBM invented the PC more than a quarter century ago, they couldn’t possibly have included all of the necessary BIOS routines for every conceivable piece of hardware on the system ROM chip. How could they? Most of the devices in use today didn’t exist on the first PCs. When programmers wrote the first BIOS, for example, network cards, mice, and sound cards did not exist. Early PC designers at IBM understood that they could not anticipate every new type of hardware, so they gave us a few ways to add programming other than on the BIOS. I call this BYOB—Bring Your Own BIOS. You can BYOB in two ways: option ROM and device drivers. Let’s look at both.
Option ROM
The first way to BYOB is to put the BIOS on the hardware device itself. Look at the card displayed in Figure 7-25. This is a serial ATA RAID hard drive controller—basically just a card that lets you add more hard drives to a PC. The chip in the center with the wires coming out the sides is a flash ROM storing BIOS for the card. The system BIOS does not have a clue about how to talk to this card, but that’s okay, because this card brings its own BIOS on what’s called an option ROM chip.
Figure 7-25 Option ROM
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NOTE Not all option ROMs say “flash”!
Most BIOS that come on option ROMs tell you that they exist by displaying information when you boot the system. Figure 7-26 shows a typical example of an option ROM advertising itself.
Figure 7-26 Option ROM at boot
In the early days of the PC, you could find all sorts of devices with BIOS on option ROMs. Today, option ROMs have mostly been replaced by more flexible software methods (more on device driver software in the next section), with one major exception: video cards. Every video card made today contains its own BIOS. Option ROMs work well but are hard to upgrade. For this reason, most hardware in PCs relies on software for BYOB.
Device Drivers
A device driver is a file stored on the PC’s hard drive that contains all of the commands necessary to talk to whatever device it was written to support. All operating systems employ a method of loading these device drivers into RAM every time the system boots. They know which device drivers to install by reading