ESDI disks are an older type that came before the IDE disks.
ESDI use the CHS (cylinder, head, sector) addressing and has a 1024 cylinder limitation. Some controller cards get around this limitation by implementing a translation scheme in the onboard controller BIOS.
The translation is totally transparent to Windows NT, and the standard disk device driver works without any change.
ESDI disks are capable of being low-level formatted with various values of sector per track, such as 53 or 63. Here are two examples:
1024 cylinders x 15 heads x 53 sectors per track x 512 bytes per sector = 398 MB
1024 cylinders x 15 heads x 63 sectors per track x 512 bytes per sector = 472 MB
Thus, using 63 sectors per track yields 74 MB more space. Windows NT is compatible with either geometry, and, depending on the disk or controller, can access cylinders beyond 1023. You can use Windows NT to create and format the disk space beyond cylinder 1023, but it cannot be accessed by MS-DOS. However, some controllers can remap the remaining cylinders beyond 1023 so that either MS-DOS or Windows NT can use the entire capacity. For example:
1632 cylinders x 15 heads x 53 sectors per track x 512 bytes per sector = 634 MB
Microsoft has tested the ESDI controllers described in the following table.
Table 17.8 Using More Than 1024 Cylinders on ESDI Controllers
Controller | Achieving Maximum Capacity |
Data Technology Corp. (DTC) Model 6282-24 | The maximum MS-DOS geometry is 63 sectors per track and 1024 cylinders. Windows NT can access the cylinders beyond 1023. Do not perform a low-level format on the disk using Head Mapping mode. |
Data Technology Corp. (DTC) Model 6290-24 | The maximum MS-DOS geometry is 63 sectors per track and 1024 cylinders. Because this controller card does not have an on-board BIOS, Windows NT cannot access the cylinders beyond 1023. |
Data Technology Corp. (DTC) Model 6290 SEZ (Dual SCSI/ESDI Controller) | The maximum MS-DOS geometry is 63 sectors per track and 1024 cylinders. Windows NT can access the cylinders beyond 1023. |
Data Technology Corp. (DTC) Model 6295-24 | The maximum MS-DOS geometry is 63 sectors per track and 1024 cylinders. This controller card does have an on-board BIOS, so Windows NT can access the cylinders beyond 1024. Do not perform a low-level format on the disk using Head Mapping mode. |
Adaptec Model 2322D | Option 1. Disable disk translation and the on-board controller BIOS. In the CMOS, use a user-defined disk type with the actual disk parameters, such as Disk Type=48, Cylinders=1632, Heads=15, Sectors per Track=53. These parameters result in a 634 MB capacity. MS-DOS is limited to the first 1024 cylinders, which makes 398 MB available. Windows NT can access beyond cylinder 1023, yielding another 236 MB. Option 2. Both MS-DOS and Windows NT can access the entire disk. Set jumpers on the controller for Disk Splitting. Disable disk translation and the on-board controller BIOS. Set up the first physical disk in CMOS as Cylinders=1024, Heads=15, Sectors per Track=53. This gives a disk capacity of 398 MB. Set up the second disk (it appears as a physical disk) in the CMOS as Cylinders=606, Heads=15, sectors per track=53. This yields another 236 MB. Windows NT sees the disk as two physical disks. |
UltraStor with PROM versions < nnnn-009 | The maximum MS-DOS geometry is 63 sectors per track and 1024 cylinders. Windows NT can access the cylinders beyond 1023. |
UltraStor with PROM versions >= nnnn-009 | The maximum MS-DOS geometry is 63 sectors per track and 1024 cylinders. Both MS-DOS and Windows NT have access to the entire disk capacity. |