Why do the speeds on fans go from Off to High, and then down to Low?

Because an electric motor should always start at the highest speed.

Electrical energy is transformed into kinetic energy.

When an electric motor goes from a dead stop to running, a gradual change of speed is not desirable. It causes too much heat.

Initial quick-starts are necessary

Large electric motors have start capacitors that discharge quickly as the motor starts.. It gives an extra "kick" to get the motor running. Once it is running, it can be slowed down to an effective operating speed.

Some motors have an extra set of wire windings called start coils. They produce extra voltage and current to help get the motor turning. When the motor reaches it's effective speed, a centrifugal switch cuts the power to the start windings.

The "high" setting on your electric fan produces a similar result since it is placed before the lower speeds.

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i could be observing the ability furnish or the button battery on the motherboard and use a multimeter to work out if the battery has 3 volts or replace it with out it the pc would not see the hdd.gl

Maybe an aggie did it.