A dynamo is a generator that produces direct current, as opposed to an alternator. It generally involves rotating an armature in a magnetic field. The armature consists of coils of wire connected to a commutator.

The commutator reverses the electrical connection to the rotating coils a number of times every revolution. This ensures that the current from the dynamo is always flowing in one direction, and is, hence, direct current. It is not stable direct current, though. You would not want to connect it to your computer without a filter and a regulator.

Dynamos have the same theory of operation as a DC motor, only in reverse. In fact, most DC motors will function as miniature dynamos if you rotate the drive shaft whilest connecting a load to its power terminals. True dynamos are designed to be more efficient for power generation, though.

Dynamos tend to be less efficient than alternators, and hence are used less often. You can produce direct current more efficiently by using an alternator with a rectifier and a filter battery or capacitor.

Dynamo is an amazing project by HP.

Essentially it is a machine code interpreter that often runs the HP8000 RISC instruction set on an HP8000 microprocessor faster than the raw HP8000 processor does!

The essential idea is that the compiler does not perfectly understand the way that the processor is used, and hence at run time the interpreter can collect data and rewrite code dynamically for greater speed.

For example, the compiler does not have access to DLLs at all, and the interpreter may be able to optimise by inlining these appropriately.

Another example, the compiler does not know what paths through the code are most frequently taken- the interpreter can find this, and inline this code allowing the cache to work more efficiently.

The speed up gained by this technology can be as much as 25% percent, although the normal speedup is nearer 4-5%. The speedups are usually different speedups than those found by the compiler, so using an optimising compiler actually gives slightly bigger percentage speedups!

However, Dynamo does not always increase the speed of the code. If it is unable to find any speedups it switches itself off.

Dynamo is based on the ideas used for an interpreter written for Self; and the same techniques are use in the Transmeta processor.

It's interesting to note that the dynamo is seperated from it's predecessors by the fact that it's magnetic field is generated by the current itself, as opposed to a permanent magnet. This allows for a much higher current to be produced. Dynamos were first put to use in light houses to power carbon arc lamps, which replaced limelight.

Dy"na*mo (?), n.

A dynamo-electric machine.


© Webster 1913.
