How To Use Error Messages; Diskette Compatibility Matrix - IBM ThinkPad T21 Hardware Maintenance Manual

Important service information
Strategy for replacing a hard-disk drive
Always try to run a low-level format before replacing a
hard-disk drive.
Attention:
you are servicing may have been changed. Be extremely
careful during write operations such as copying, saving, or
formatting. If you select an incorrect drive, data or
programs can be overwritten.

How to use error messages

Use the error codes displayed on the screen to diagnose
failures. If more than one error code is displayed, begin the
diagnosis with the first error code. Whatever causes the
first error code may also cause false error codes. If no
error code is displayed, see if the error symptom is listed
in the Symptom-to-FRU Index for the computer you are
servicing.

Diskette compatibility matrix

The compatibility of each of the drives with the diskettes
for it is as follows:
Diskette
drive
3.5-inch
2
ThinkPad T20, T21, T22, T23 (MT 2647/2648)
The drive startup sequence in the computer
Diskette
capacity
1.0 MB
2.0 MB
4.0 MB
Compatibility
Read and write
Read and write
Not compatible