Assigning Drive Letters for Removable Media

Whenever a removable media device is present, the Windows 95 volume tracker ensures that the correct media is in the device and reports improper media removal or insertion.

The volume tracker keeps track of removable media in two ways:

• On non – write-protected floppy disks, the volume tracker writes a unique ID in the disk's FAT header. This ID is different from the volume serial number
• On write-protected floppy disks, the volume tracker caches each disk's label, serial number, and BIOS parameter block

Windows 95 supports existing removable media with MS-DOS – compatible partitions, which usually are created by using Fdisk utilities from other vendors. You can use Fdisk for Windows 95 to create partitions on INT 13-based removable media, as described earlier in this chapter.

Windows 95 does not perform volume tracking based on the volume serial number because all removable media do not have serial numbers or some might have duplicate serial numbers (as is the case with bulk-formatted floppy disks). Therefore, the file system driver must assign unique serial numbers to removable media the first time there is a request to mount the specific media, unless unique numbers have already been written to the media. These unique numbers identify the media for volume tracking.

Note

For volume tracking with NEC® floppy-disk change detection, if the system detects a change line on a volume, the change line is used for subsequent I/O requests to the media.

You can control the number of drive letters to be reserved during system startup for each removable media drive.

To reserve drive letters for removable media

1. In the System option in Control Panel, click the Device Manager tab.
2. In the hardware list, double-click the item that represents the removable device.
3. In the Properties dialog box, click the Settings tab.
4. In the Reserved Drive Letters area, select a letter in the Start Drive Letter list to define the first drive to be assigned to this device. In the End Drive Letter list, select the last drive to be assigned to this device. Click OK
5. To close the System properties dialog box, click OK.
6. When prompted, restart the computer.

The MaxRemovableDrivePartition entry in the Registry allocates the drive letters to be used by partitions on removable media. If this entry is not present in the Registry, the number of drive letters to be assigned is based on the number of partitions present on the media when the system starts. If no media are present at startup, Windows 95 reserves one drive letter for each of the removable media.

To support variable-sized disks and partitions, Windows 95 recalculates the disk geometry every time a media change is detected. If you insert media with more partitions than specified by the MaxRemovableDrivePartition entry in the Registry, a message warns you that some partitions on the media are not accessible in the current configuration and prompts you to increase the value of MaxRemovableDrivePartition.