Bus Mastering
The PCI bus architecture includes a technology called bus mastering that allows an ex-
pansion card to directly transfer data to and from the PC’s main memory (RAM) and to
and from other bus mastered peripheral device controllers without the need to pass
through the CPU. Bus mastering allows the PCI bus controller to transfer data from a PCI
device directly to memory. This frees the CPU to perform other tasks, thereby making the
entire system more efficient.Local Bus Architectures
Typically, the expansion bus is independent of the system bus structures used by the core
system components. The CPU, chipset, and main memory uses an internal or system bus
to move data between themselves interacting with the expansion and I/O bus when
needed. The internal system bus is said to be “local” to the CPU and other internal devices.
Thelocalbusallowsthedevicesthatattachtoittheabilitytooperateandmovedataatthe
higher speeds offered by internal bus architectures. The bus speeds of the local bus and
the expansion and I/O buses are no longer very different, which has reduced the need to
use local bus architectures like the VESA local bus (VL-bus).Portable PC Interface
Portable PCs, such as laptops, notebooks, palmtops, and other compact and portable
computers, use a special expansion interface—the PC Card. The PC Card interface allows
specially designed expansion cards to be inserted and used immediately, while the system
is running and without the need to open the computer’s case. This interface, formerly
known as the PCMCIA (Personal Computer Memory Card International Association)
interface after the standards body that developed it, uses a 68-pin socket that connects
directly to the computer’s system bus. PC Cards are inserted into the socket to add re-
sources or devices to the computer. Figure 11-7 shows a notebook computer with a PC
Card network adapter being inserted.PC Card Characteristics
PC Cards are credit-card sized expansion cards that are used to add not only the adapter
or controller for a peripheral device, but the entire device itself. PC Cards can be used to
add more memory, a hard disk, a modem, a network adapter, a sound card, or more. The
cards that fit into the PC Card slot are all a standard height and width of 85.6 millimeters
(mm) by 54 mm, or approximately 3 1/3 inches by 2 ¼ inches. Where PC Cards differ is in
their thickness, with thicker cards containing usually more function or capability.(^226) PC Hardware: A Beginner’s Guide