Reversible computing

The term Rechnerreversibilität or English Reversible computing refers to an architecture for computers that are ( at least approximately ) is reversible, in their calculations, ie from the end result and the initial state could be restored.

Important motivation for research on reversible computer architectures is the desire to avoid the theoretical limit of the energy efficiency of today's computer architecture. This is especially with regard to the construction of quantum computers interesting, as these heat generation irreversible logic circuits would lead to malfunction.

Neumann - Landauer limit

Today's computer architecture is based on irreversible logic. This means that is lost when performing logical operations information. So a simple AND, for example, has two input signals but only one output signal. So it's lost a bit and the number of possible logic states is reduced from 4 to 2

Treatment of logic states such as physical, so they are subject to the rules of thermodynamics. Thus, a reduction in the number of states from 2 to 4 leads to a reduction of entropy to ( k the Boltzmann constant). The Entropiereduktion in turn requires that an amount of heat is released at least. This lower limit for the energy that is used per logical operation in modern computers, is called Neumann - Landauer limit ( by Rolf Landauer and John von Neumann ).

Logical states how to treat physical, is not as far-fetched as logic states must be represented by physical.

Reversible logic processes

Logical operations need not be irreversible. One can define reversible logical operations and how Landauer has shown logically reversible processes are always physically reversible ( Landauer 's principle ).

In particular, it can be shown that all logical operations can be represented as a combination of reversible operations. Theoretically, can also be reversible logic a computer build. In addition, many publications of some of well-known authors exist, will discuss the concepts and mechanisms on this topic. Nevertheless, Reversible computing is still used today for research purposes only.

Disadvantages

Since reversible logic, the information must be retained, occurs in a calculation of a large amount of additional bits that must be stored.

Weblink

Two Types of Mechanical Reversible Logic

• Computer Architecture