The rpm command measures the rotation speed of the floppy drive.
The correct drive speed is important when writing to floppy, as the effective track space is reduced if the disk is rotating faster than normal. This is critical for the 8K sector formats used by some Amstrad CPC and Spectrum +3 disks.
To measure the floppy drive rotation rate use:
SAMdisk rpm a:
This will measure the speed over a few seconds, and display the settled value.
Normal drive speeds are:
- 3.5" = 300rpm (usually)
- 5.25" = 360rpm
- 3" = 300rpm
The speed of 3.5" and 5.25" drives are generally fairly reliable.
However, 3" drives (used by Amstrad machines) have been seen to vary wildly from their rated speed! Adjustment is possible through a hole in the top of the motor unit. I also recommend aiming for around 292rpm if you intend to write disks containing 8K sectors.