Hardware Reference
In-Depth Information
the OS rather than the hardware.
The OS then interfaces with or talks to the BIOS or driver layer. The BIOS consists of all the
individual driver programs that operate between the OS and the actual hardware. As such, the OS
never talks to the hardware directly; instead, it must always go through the appropriate drivers. This
provides a consistent way to talk to the hardware. It is usually the responsibility of the hardware
manufacturer to provide drivers for its hardware. Because the drivers must act between both the
hardware and the OS, the drivers typically are OS specific. Thus, the hardware manufacturer must
offer different drivers for different OSs. Because many OSs use the same internal interfaces, some
drivers can work under multiple OSs. For example, drivers that work under 32/64-bit versions of
Windows 7 and 8 usually work under the corresponding versions of Vista; drivers that work under
Windows XP usually work under Windows 2000 and NT. This is because Windows 7/8 and Vista
are essentially variations on the same core OS, as are Windows XP, Windows 2000, and NT.
Although Windows 7/8 and Vista were based on Windows NT, the driver model has changed enough
that they generally can't use the same drivers as XP and earlier NT-based OSs.
Because the BIOS layer looks the same to the OS no matter what hardware is above it (or underneath,
depending on your point of view), the same OS can run on a variety of systems. For example, you can
run Windows on two systems with different processors, hard disks, video adapters, and so on, yet
Windows will look and feel pretty much the same to the users on both of them. This is because the
drivers provide the same basic functions no matter which specific hardware is used.
As you can see from
Figure 5.1
, the application and OS's layers can be identical from system to
system, but the hardware can differ radically. Because the BIOS consists of drivers that act to
interface the hardware to the software, the BIOS layer adapts to the unique hardware on one end but
looks consistently the same to the OS at the other end.
The hardware layer is where most differences lie between the various systems. It is up to the BIOS to
mask the differences between unique hardware so that the given OS (and subsequently the
application) can be run. This chapter focuses on the BIOS layer of the PC.
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. The BIOS and CMOS RAM are two separate components.
The BIOS on the motherboard is stored in a 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 settings in the BIOS Setup are stored, and it is actually a clock chip with a few extra
bytes of memory thrown in. It is usually called the
CMOS chip
because it happens to be 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, the chip is actually volatile,
meaning that without power, the time/date settings and the data in the RAM portion will in fact
be erased. Many consider this chip nonvolatile because it is designed using CMOS technology,
which results in a chip that requires little power compared to other chips. A small battery can
provide that power when the system is unplugged. This battery-powered clock/memory chip is
