Chapter 6: Device Drivers
processor architectures. It is rarely used in workstation systems because its electrical installation
is very complicated as compared to other buses (each SCSI chain must be terminated in order to
function correctly).
❑ Parallel and Serial Interfaces— These are present in most architectures regardless of the design
of the overall system. These are extremely simple and very slow connections to the outside world
and have been with us for an eternity. They are used to address slow devices such as printers,
modems, and keyboards that place no great performance demands on the system.
Regardless of the processor architecture employed,systems usually have not just one but a combination
of buses. Current PC designs generally include two PCI buses interconnected by abridge. For compatibil-
ity reasons, they sometimes also feature an ISA bus (mostly with just one slot). Some buses such as USB
or FireWire cannot be operated as main buses but always require a further system bus via which data are
passed to the processor. Figure 6-2 shows how different buses are linked in a system.
RAM CPU
I/O Memory
bus
PCI #0
PCI #1
BridgePCI
PCI Slots
Root-Hub
Hub Webcam
Mouse Keyboard
SCSI
Controller Scanner
Hard Disk
Hard Disk CD ROM
USB
Controller
Figure 6-2: Linking different kinds of buses.
Interactionwith the Peripherals
Let us turn our attention to the methods that are available to communicate with peripherals. There are
several ways of communicating with the hardware attached to the system.
I/O Scheduling
OneoptionistousetheI/OportsfoundonIA-32andmany other architectures. In this case, the kernel
sends data to an I/O controller. The device for which the data are intended then is identified by means of