Direct access to SCSI devices on Mac OS X

NOTE: The text below is only of historical value - MakeMKV no longer uses "direct access" mode, can work with nearly all drives in "OS access" mode and works with every drive in DASPI mode.

Almost every optical drive available today is a SCSI MMC device - no matter if it is internal CD-ROM reader or external Blu-ray writer. SCSI MMC is a standard that defines interaction between drive and software. Usually operating system contains a driver that implements SCSI protocol and provides device access to applications - like allowing one to open files from DVD disc. Windows, Linux and Mac OS X all provide interfaces that allow applications direct access to the drive - MakeMKV uses these interfaces to read data from the disc and query drive state.

"Direct access" sounds really scary - the application that has direct access to the drive can issue any command and do anything drive allows - for example eject the disc or read volume label from disc. That's why direct drive access is usually restricted and restriction varies by operating system. On Linux there are no special restrictions - any user who has access to the drive can issue any command. On Windows only members of Administrators group have such access - that's why MakeMKV requires administrator privileges on Windows.

On Mac OS X access depends only on the drive type. If the drive is a read-only device that can't write to any media ( either CD-ROM, DVD-ROM or BD-ROM) then access is blocked. The rationale is that direct access is dangerous and application may request drive to perform any action, like eject the disc (one really can't erase a disc in a read-only device). However, if the drive is capable of writing any media (for example Blu-ray reader that can write CD and DVD media) then all access is allowed to any user. This policy is beyond our comprehension - our only explanation is that weed is really easily available to designers in Cupertino, CA. Practically that means that if you have any drive that is read-only device, then it will not be accessible to MakeMKV. Luckily most modern drives usually are combo drives that can write at least CD media - these drives are accessible to MakeMKV. Even if the drive is not accessible there is a way to enable access to all drives - that requires changes to the system plist file and rebooting the system. Please see our forum for details.