Windows 95 uses layered block device drivers to manage input and output to block devices such as disks and CD-ROM drives. A block device is a device such as a disk drive that moves information in groups of bytes (blocks) rather than one byte at a time. Layered block device drivers are 32-bit, flat-model device drivers that run in protected mode. These drivers support conventional and SCSI disk drives, plus partitioned and unpartitioned removable media. Windows 95 also uses layered block device drivers to manage Windows 3.x FastDisk drivers, MS-DOS – based real-mode device drivers, and Windows NT miniport drivers.
Each layered block device driver can be loaded dynamically, so the appropriate driver can be loaded or unloaded as needed without restarting the computer. Although the drivers are virtual device drivers (VxDs), they do not use the standard virtual device services and APIs. Instead, the I/O Supervisor provides the services and functions the device drivers need to complete their tasks.
Specifically, the block I/O subsystem in Windows 95 provides the following:
For more information about the block I/O subsystem, see Chapter 31, "Windows 95 Architecture."