Direct Memory Access - HP Compaq dc7800 Series Technical Reference Manual

System Support
System Board
Connector
PCI slot 1 [1]
PCI slot 2 [1]
PCI slot 3 [2]
NOTES:
[1] SFF and CMT only
[2] CMT only
The PCI interrupts can be configured by PCI Configuration Registers 60h..63h to share the
standard ISA interrupts (IRQn).
✎
The APIC mode is supported by Windows NT, Windows 2000, and Windows XP, and Windows
Vista operating systems. Systems running the Windows 95 or 98 operating system will need to
run in 8259 mode.

4.3.2 Direct Memory Access

Direct Memory Access (DMA) is a method by which a device accesses system memory without
involving the microprocessor. Although the DMA method has been traditionally used to transfer
blocks of data to or from an ISA I/O device, PCI devices may also use DMA operation as well.
The DMA method reduces the amount of CPU interactions with memory, freeing the CPU for
other processing tasks. For detailed information regarding DMA operation, refer to the data
manual for the Intel 82801 ICH9 I/O Controller Hub.
4-8
Table 4-5.
PCI Interrupt Distribution
PIRQ PIRQ PIRQ
A B C
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System Interrupts
PIRQ PIRQ PIRQ
D E F
A B
D A
C D
PIRQ PIRQ
G H
C D
B C
A B
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