Acer Altos 500 Series User Manual page 108

Computer Hangs, or SCSI Controller Cannot Always Find the
Drives
Check SCSI parity for consistency and be sure SCSI termination is set correctly.
Check cable length and integrity. Check pin-1 orientation.
If the SCSI controller LED remains on when the computer hangs, the host
adapter may be interfering with your computer's operation. It may be installed
in a motherboard slot that does not support First-Party DMA (i.e., Bus Master)
data transfers. See your computer documentation.
Altos 500 Series User's Guide