Dell Precision 420 - Manual (Page 74)

Microphone Jack
You can use the microphone jack (see Figure 11) to attach a nondynamic monaural microphone for personal computers. Connect the audio cable
from the microphone to the microphone jack. The microphone input is a mono source with maximum signal levels of 130 millivolts root mean
squared (mVrms).
Figure 11. Microphone Jack
Line-Out Jack
You can use the line-out jack (see Figure12) to attach most computer speakers. The line-out jack is not amplified, so speakers with integrated
amplifiers are required. Connect the audio cable from the speakers to this jack.
Figure 12. Line-Out Jack
Line-In Jack
You can use the line-in jack (see Figure 13) to attach record/playback devices such as cassette players, CD players, and VCRs. Connect the line-
out cable from any of these devices to the line-in jack on the back of your computer.
Figure 13. Line-In Jack
Interrupt Assignments
Problems can arise if two devices attempt to use the same IRQ line. To avoid this type of conflict, check the documentation for the default IRQ line
setting for each installed device. Then consult Table 9 to configure each device for one of the available IRQ or other lines.
Table 9. Interrupt Assignments
2 DATA I Data in
3 +DATA O Data out
4 GND N/A Signal ground
NOTE: Interrupts for the integrated sound, NIC, and both SCSI channels are assigned dynamically by the system basic input/output
system (BIOS).
IRQ Line Used By/Available
IRQ0 System timer
IRQ1 Keyboard controller
IRQ2 Interrupt controller (enables IRQ8 through IRQ15)
IRQ3 COM2 and COM4 serial ports (if enabled in System Setup program)