Matt Snider and Jeremy Tinley describe a problem with "the ATA 4 Device Manager and the new, redesigned File Manager under Mac OS 8. The bug appears only when copying from an IDE-ATA internal hard drive to a SCSI device. The bug does not appear when copying from SCSI to SCSI, SCSI to IDE-ATA or from IDE-ATA to floppy or from SCSI to floppy.
The symptom is a freeze when copying a file large enough to result in the display of the estimated time remaining calculation display in the copy file window (this is a function of the size of the file and the speed of the drive).
Turning on virtual memory prevents this the occurrence of this bug.
This may be the cause of previous reports of freezes and crashed in Mac OS 8 when copying files to external drives. Apple also has a web page that describes a couple of other problems that can occur when copying files in Mac OS 8.