Konrad Zuses Contributions to the Modern Computer

Konrad Zuse must be credited with the following fundamental inventions in the area of computing development, where most of them were implemented in the machines Z1 (1938), Z3 (1941) and Z4 (1945), with the exception of the Plankalkül:

• The use of the binary number system for numbers and the circuits.
• The use of floating point numbers, along with the algorithms for the translation between binary and decimal and vice versa.
• An algorithm for the non-restoring calculation of the square-root. With this algorithm, the square-root can be calculated with n steps, if n is the number of digits. This fine method was not known in the US in 1949.
• The carry-look ahead circuit for the addition operation.
• Look-Ahead: The program is read two instructions in advance, and it is tested whether memory instructions can be performed ahead of time.
• Pseudo-memory: In case the look-ahead mechanism finds that a number that is to be restored is needed again within the next two instructions, the number id placed in a register of mechanical contacts where it is available with no access time. For this purpuse, the memory has two registers of reading contacts.
• Special values (Sonderwerte): If a result exceeds the capacity of the arithmetic unit, it is designed as Sonderwert. This principle guarantees that the machine always calculates correctly.
• The most unusual feature was undoubtedly the mechanical binary cells that made up the memory. The memory has 64 words with 32 bits (Z1 and Z4). These devices were completely different from mechanisms in contempory cash registers or desk-top calculators. The elements could be used not only for storage, but also for calculation, for example for address coding. A relay memory would have required about 2500 relays which would have more than doubled the size and the weight of the machine Z4.
• The Plankalkül as the first complete high-level language of the world in 1945/46 (final edition).