For an Adaptec 2940UW with EZ-SCSI 4.0 on Windows 98, the Pioneer supplied drivers weren't enough.
Drive would identify and do directory, but baulk at any kind of file transfer. This file provides EZ-SCSI 5.0 bare disks to upgrade not only ASPI8DOS.SYS and ASPICD.SYS, but other system files as well. ASPICD.SYS reports the CD-ROM drive data to Windows 98 so it picks up properly. Found out at www.adaptec.com and found driver on Compaq support site.