Hard Disk Monitoring

I'm curious about what the APM levels correspond to in Windows 7. I know this much:

AMP Level
0 = Disabled
1 = Minimum power consumption with standby
2-127 = Intermediate power management levels with standby
128 = Minimum power consumption without standby
129-253 = Intermediate power management levels without standby
254 = Maximum performance and power consumption

What do the ranges mean? For example, what would be the difference between APM 2 and APM 125? I was unable to find any useful information online about APM levels. Any help would be appreciated!

These levels are defined by the manufacturer of the actual drive.
It is completely independent from the current OS version, but only depends on the drive.

Most manufacturers do not tell anything about the difference between these levels.
Usually manufacturers define only some discrete levels, so in most cases 2 .... 127 are the same, 129 ... 253 are the same and so.
But it depends on the manufacturer of the actual drive, so you may ask directly about the proper model if they define any differences in these levels.