What type of motors are used in computers?

Answer 1

In any typical application (like desktop/personal computers), there would be two types of motors: brushless motors and stepper motors.

Brushless motors are usually used to run things that need to run without exact position control. These kind of motors are used in the computer cooling system (ie. cooling fans), and in some motive applications like optical media (driving the CD/DVD discs). These motors are generally a very good choice for two reasons: the don't have many parts that wear out (like brushed DC or AC motors), and their speed can be controlled rather precisely. These motors are driven with varying AC pulses (most commonly squares rather than sines), and usually have three leads (more rarely four) attached directly to the stator. If direct and precise speed regulation is not that important, they will usually just expose the positive and negative leads (typically red and black), keeping their driving electronics hidden inside the enclosure (in most cases - on a small disc-shaped PCB right under the rotor). They sometimes also expose a third lead for counting rotations, like cooling fans do (yellow wire). When mounted inside components (like DVDs), they are usually attached directly to the circuit board (typically glued/screwed in place). In most cases, these motors drive their load (fan, CD etc.) directly. They consist of many coils (how many - depends on construction) on the stator, and one permanent magnet on the rotor. When turned by hand, they usually turn freely.

Stepper motors are a more specific subset of brushless motors, giving much finer control of position, and they are generally much more precise. Stepper motors can also stop at a precisely defined position or turn only a precisely defined angle ("make a step", or halfstep etc. - thus "stepper" motors). These motors are used in optical media head drivers (ie. the motor that regulates where the reading/writing head is positioned), as well as floppy disk drives (very rare devices nowadays) and hard disks. These motors are also heavily used in inkjet/ribbon printers (printing head positioning), and in scanners (reading head positioning) - in general in all applications where invariability and precision are important. In most cases*, stepper motors drive their load (printing/reading heads etc.) indirectly through some form of a gearing mechanism - most notably a worm drive - to give finer control over the movement. They consist of many coils on the stator, and a matching set of small, powerful (rare earth) magnets on the rotor, thus enabling the stepping action. When turned by hand, they will show resistance and a tendency to "jump into" positions at regular intervals.

It is worth noting that while brushless motors do generate a lot of "chatter" on the power line (feedback from the driving mechanism, ie. noise on the line) while they spin, this is still nothing compared to brushed motors which can vary widely (and wildly). Also, brushless motor "chatter" can be predicted (and thus counteracted) with fair consistency.

* the most significant and commonplace deviation is the hard disk (HDD) platter drive. These stepper motors are used for their extremely precise speed control, and the platters are attached directly to them. These motors are designed with speed in mind as well (typically running at 7200 revolutions per minute, sometimes higher), but their fine speed and position control is used to make sure that the platter is in the correct "reading" position when the reading head is in the correct "reading" position as well, at those high speeds.

Answer 2

Computers don't contain motors.