3Com 3C971-F manual Introduction

1-4 CHAPTER 1: INTRODUCTION

The PCI specification defines two types of PCI devices: a target and a master. A target is a device that accepts commands and responds to the requests of a master. The master, or bus master, is a more intelligent device that can conduct processing independently of the bus or other devices. A bus master device shares the bus with the main processor and targets. Bus mastering allows a peripheral device to take control of the system bus and not rely on the central processor. The 3C971-F adapter is a bus master device.

The PCI specification supports the following features:

■High performance. The PCI local bus runs at a clock speed of 33 MHz and employs a 32-bit data bus that supports multiple peripheral components and add-in cards at a peak bandwidth of 132 MBps, up to an order of magnitude greater than that of other PC buses (ISA, EISA, and MCA).

■Automatic configuration. A PCI adapter has configuration specifications set in on-board memory and provides installation information to the computer at start-up.

■Shared slots. The PCI specification calls for “shared slots,” which denotes the shared expansion backplate slot. This shared backplate slot provides access to one of two types of adapters: a PCI adapter and an ISA adapter, for example, or a PCI adapter and an EISA adapter. Only one adapter at a time can be installed in a shared slot. Manufacturers are currently producing computers that support the PCI bus in conjunction with conventional ISA or EISA buses in the same chassis.

For detailed information about the PCI local bus, consult the PCI specification.