Figure 2.13 illustrates a representative hardware configuration for an "AT" (WD1003-compatible) disk controller.
Figure 2.13 AT Disk Controller Hardware Configuration
Each "AT"-type disk controller is assumed to support at most two disk devices, which might have different geometries. Figure 2.14 illustrates the corresponding layered drivers for these disks.
Figure 2.14 AT Disk Driver Layers
The system "AT" disk driver is designed to manage up to six disk controllers, each with up to two disks attached. This driver supports any NT file system with a partition on one of its disks. Depending on how a particular end user partitions the disks in a Windows NT machine, more than one NT file system driver might be layered over the system "AT" disk driver, including any of the system-supplied FAT, NTFS, and HPFS FSDs.