Motherboards and Buses - Upgrading and Repairing PCs - page 285

sion slots in high-performance systems. By early 2006, most motherboards featured PCI
Express x16 slots in place of AGP.
To learn more about AGP, see “ Accelerated Graphics Port ” in Chapter 4 , “ Motherboards
and Buses , ” in Upgrading and Repairing PCs, 19 th edition , available in its entirety on the
DVD packaged with this topic.
System Resources
Systemresourcesarethecommunicationschannels,addresses,andothersignalsthathard-
ware devices use to communicate on the bus. At their lowest level, these resources typic-
ally include the following:
• Memory addresses
• IRQ (interrupt request) channels
• DMA (direct memory access) channels
• I/O port addresses
Theseresourcesarerequiredandusedbymanycomponentsofyoursystem.Adaptercards
need these resources to communicate with your system and accomplish their purposes.
Not all adapter cards have the same resource requirements. A serial communications port,
forexample,needsanIRQchannelandI/Oportaddress,whereasasoundcardneedsthese
resources and at least one DMA channel.
As systems increased in complexity from the late 1980s on, the chance for resource con-
flicts also increased. The configuration problem came to a head in the early 1990s, when
manual configuration was the norm. Starting around that time, Microsoft and Intel de-
veloped PnP, which allowed for automatic detection, management and configuration of
hardware, usually without user involvement. Windows 95 was the first PnP-aware PC op-
erating system (OS), and by the time it was released, most hardware began supporting the
PnP standard. Plug and Play was later superceded by Advanced Configuration and Power
Interface (ACPI), which combined device configuration and power management into a
single specification.
Modern systems with ACPI and modern buses such as PCI and PCI Express rarely have
problemsconfiguringtheseresources.Invirtuallyallcases,theconfigurationwillbeauto-
matic and trouble free.
Interrupts
Interrupt request channels, or hardware interrupts, are used by various hardware devices
to signal the motherboard that a request must be fulfilled. This procedure is the same as a
student raising his hand to indicate that he needs attention.