TITLE:Supporting AT and IDE Disks on NetWare 386 with the ISADISK 
                   Driver
      DOCUMENT ID#:FYI-P-3409
              DATE:5/17/91
           PRODUCT:Netware
   PRODUCT VERSION:3.11
        SUPERSEDES:NA

           SYMPTOM:NA

ISSUE/PROBLEM

The ISADISK disk driver supplied with NetWare 386 is intended to support 
all drives that comply with the original IBM PC/AT specification. DOS uses 
a BIOS INT 13 to get the disk size and geometry. The BIOS looks at the CMOS 
setup of the machine and finds the disk type. Then it will look up that 
disk type in its tables in EPROM and puts a pointer to that disk type in 
INT 41 for drive "C" and INT 46 for drive "D." This has worked well in the 
past until several new developments in recent years have presented new 
challenges for disk drivers to support these features.
 
The issues presented by these new drives:
 
1. The development of drives not included in the machines BIOS tables.  
These drives allow there to be a user defined drive type and the interrupt 
is redirected to point to that drive. In some cases the controller may 
perform this redirection.
 
2. The development of drives with more than 1024 cylinders. BIOS INT 13 
supports only 10 bits to define the number of cylinders. This imposes a
limit of 1024 cylinders. Some vendors get around this problem by providing 
controllers that perform a translation so that a drive is presented to the 
operating system that has less than 1024 cylinders. This method works most 
of the time but in some instances does not allow the entire capacity of the 
drive to be used.

3. The development of secondary controllers. Vendors such as Compaq 
Computer Corporation have introduced secondary controllers that allow two 
additional drives to be used. For DOS, Compaq provides a device driver that 
must be loaded in order to support the secondary controller.

4. IDE Disks. IDE disks solve some of these problems and create others. A 
specification has been submitted to ANSI. Until a final specification is 
adopted that everyone must comply with, there may be difficulties 
supporting some drives. The IDE drive is a block device and thus unlike the 
ESDI and MFM drives, it can work as any size drive that is equal or smaller 
than it. For example, if the user wants to install an 80 megabyte drive in 
a system, he can choose a definition for an 80 megabyte or smaller drive 
and have the drive work correctly with the capacity of that definition.

Dealing with the issues with the ISADISK.DSK driver.
Secondary controllers. If ISADISK.DSK does not recognize the secondary 
controller, reload the driver with the "/l" option. This allows a 
redirected BIOS table to be recognized and will assume a full table. When 
using the "/l" option special attention should be made to ensure that the 
drive is registered correctly. IDE Drives. The ISADISK.DSK driver works 
with most of the IDE drives. Using the "/b" option will allow some of the 
IDE drives to work that otherwise can't. This option instructs the driver 
to skips it's checks for NetWare ready and CCM.

User defined or drives with more than 1024 cylinders. If NetWare cannot see 
the full capacity of the drive, you can use a controller that provides 
translation. Another option is to use a drive that has the same cylinders 
and heads as the actual drive but will give you more capacity than the 
drive type that you are currently using. A "CCM" or "NetWare Ready" drive 
will allow the entire capacity of the drive as this information is written 
on the disk.