Question about PC Desktops
IRQ, DMA, and other Computer Creatures
IRQ's (Interrupt Request) LinesIRQ's are hotlines to the main computer (CPU) that allow devices connected to the computer to signal the CPU that they need immediate attention. If you're a Batman fan, think of IRQ's as the Batphone - getting his attention immediately.
Not all devices require IRQ lines, which is good news because in modern (post IBM XT) computers, we only have 16 of them. Of those, 3 are already dedicated to the main system board itself - the system timer, keyboard, and memory parity error signal. That leaves only 13 for all the other devices connected to your computer. This is why IRQ conflicts are probably the #1 problem faced by computer users when they add hardware to their computer.
Its a general rule for ISA-type systems (the standard computer architecture used in most IBM compatible systems) that IRQ lines CANNOT by shared with multiple devices except under special circumstances. For this reason, a good understanding of what IRQ's are assigned to what devices is essential in avoiding conflicts. The table below is a general outline for standard IRQ assignments.IRQ DEVICE USED in AT, 386, 486, and Pentium Computers
0 System Timer
1 Keyboard Controller
2 Tied to IRQs 8-15
3 COM 2
4 COM 1
5 LPT2 or Sound Card
6 Floppy Diskette Controller
7 LPT 1
8 Real Time Clock
9 Substitutes for IRQ 2
10 Not Assigned
11 Not Assigned
12 PS/2 Mouse Port
13 NPU (Numerical Processing Unit)
14 Primary Hard Disk Controller
15 Secondary Hard Disk Controller
Depending on the computer's configuration, add-in devices such as SCSI controllers, sound cards, modems, cd-roms, etc. will want an IRQ line that is already used by another device, and thus we have what is commonly referred to as an IRQ Conflict.
The most common IRQ conflicts seem to be between two COM ports, generally a mouse and modem conflict that ends up freezing the mouse whenever the modem is activated. The table below explains each IRQ and the most common devices each may use.
Posted on Oct 18, 2008
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To enable DMA mode using the Device Manager
Open Device Manager.
Double-click IDE ATA/ATAPI Controllers to display the list of controllers and channels.
Right-click the icon for the channel to which the device is connected, select Properties, and then click the Advanced Settings tab.
In the Current Transfer Mode drop-down box, select DMA if Available if the current setting is "PIO Only."
If the drop-down box already shows "DMA if Available" but the current transfer mode is PIO, then the user must toggle the settings. That is:
Change the selection from "DMA if available" to PIO only, and click OK.•
Then repeat the steps above to change the selection to DMA if Available.
Oct 14, 2007 | PC Desktops
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