|
What
Is A DMA Channel?
GENERAL
DMA
stands for "Direct Memory Addressing". Modern systems
typically have two DMA controllers each having four DMA channels
for a total of eight. Numbered 1 – 8, DMA channels are system
resources assigned to hardware devices in your system.
A
DMA channel allows a hardware device to bypass your processor
and directly access system memory. This can greatly increase system
performance. Not every device in your system needs a DMA channel.
Check the list at the end of this article for typical assignments.
Plug
and Play operating systems like Windows 95 and 98 usually do a
good job handing out DMA channels to hardware devices with minimal
problems.
CONFLICTS
Like
IRQs, a DMA channel can only be assigned to one hardware device.
If two devices get the same DMA channel, both devices may fail
to work or your system may crash.
The
biggest cause of DMA conflicts is the sound card. Most system
designers advise installing the sound card first before installing
other devices that require DMA channels (scanners, CD-ROMS etc.)
This is because sound cards tend to be very picky regarding what
exact DMA channels they want to control.
VIEWING THE ASSIGNMENTS
Under
Windows 95 / 98:
- Choose
Start, Settings, Control Panel
- Double
click the System icon
- Choose
the Hardware tab
- Click
your right mouse button on My Computer (at the top of the list)
- Choose
Properties
- Choose
DMA
Under
Windows NT:
- Choose
START, PROGRAM FILES, ADMINISTRATIVE TOOLS
- Choose
Windows NT Diagnostics
- Click
the Resources tab
- Choose
DMA
MOST COMMON DMA ASSIGNMENTS
These
are the most common DMA channel assignments used in today's PCs.
Check yours to see if they match.
|
Number
|
Common
Assignment
|
|
1
|
Sound
Cards
|
|
2
|
Sound
Cards, Network
|
|
3
|
Floppy
Drive
|
|
4
|
ECP
or EPP Parallel Port
|
|
5
|
Not
Used
|
|
6
|
OPEN
|
|
7
|
OPEN
|
|
8
|
ISA
IDE Hard Drive Controller
|
Close
Window
|
