Thanks very much, Eskimo!I am developing an application that uses disk arbitration to find out which devices are connected to a machine and react to connect/disconnect events./dev/disk0 (internal): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme 1.0 TB disk0 1: EFI EFI 314.6 MB disk0s1 2: Apple_APFS Container disk1 1.0 TB disk0s2 /dev/disk1 (synthesized): #: TYPE NAME SIZE IDENTIFIER 0: APFS Container Scheme - +1.0 TB disk1 Physical Store disk0s2 1: APFS Volume Macintosh HD 509.7 GB disk1s1 2: APFS Volume Preboot 44.5 MB disk1s2 3: APFS Volume Recovery 513.5 MB disk1s3 4: APFS Volume VM 2.1 GB disk1s4 /dev/disk2 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: FDisk_partition_scheme *1.0 TB disk2 1: Windows_NTFS TOSHIBA EXT 1.0 TB disk2s1 /dev/disk3 (disk image): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme +10.1 MB disk3 1: Apple_HFS File Transfer 10.0 MB disk3s1As the output of Disktutil above, I assume all ejectable drivers are the external drives(such as .dmg, CD/DVD drives, external hard drive...), so I can use kDADiskDescriptionMediaEjectableKey to identify them as below? or any other way?ASessionRef session = DASessionCreate(NULL); if (session) { disk = DADiskCreateFromBSDName(NULL, session, "/dev/disk2s1"); if (disk) { descDict = DADiskCopyDescription(disk); if (descDict) { object = CFDictionaryGetValue(description, kDADiskDescriptionMediaEjectableKey); if (object) { if (object == kCFBooleanTrue) { return true; } } } } }As you mentioned, I can use kDADiskDescriptionDeviceInternalKey to identify the local driver, so I can also use ‘not internal’ to replace the above approach?