Drum memory
The drum storage (English: drum memory ) was an early form of data storage in computer systems, which was widespread in the 1950s and into the 1960s, and today can be seen as a precursor to the hard disk. The method was developed in 1932 in Austria by Gustav Tauschek. On 1 July 1933 he announced his invention as " Electromagnetic memory for numbers, and other data, especially for accounting facilities " at the German Imperial Patent Office and obtained on the patent DRP 643803rd In many early computer systems, the main memory has been formed by such a drum system on which data and programs were held during the calculation. Drum store and were later replaced until the introduction of the semiconductor memory by core memory, which was faster and did without moving parts.
Operation
A storage drum composed of a rotating metal cylinder which is coated on the outer surface with a ferromagnetic material. The function you can imagine how a hard drive, only that the data is stored on a cylindrical surface instead of a flat disk.
A major difference to the hard drive is that the drum store there is usually a separate read-write head for each track.
Also magnetic disks as a " drum " memory used - the end of the development were - for example, when TR 440. These were of considerable diameter: about 1 meter. Here, too, each track ( the drum or plate ) had its own write.
Therefore, no head movements, and seek times are needed to go to a particular track. The access time to a specific record in a drum is so small, the controller must only wait until the required data appear under the correct reading head. The power of the drum memory is therefore almost exclusively determined by its rotational speed, while a hard drive and the speed of the head positioning flows.
The system clock was sometimes generated by a specially designed reading head, the track contained a fixed magnetized pattern. This allowed the synchronous data access be ensured in the instruction execution of the program.
When these systems were used as the main memory, the throughput was of course the crucial issue. Programmers therefore often tried, artfully optimized organize code and data on the drum to minimize the time for access to the respective next instruction or the next record. These execution times were measured, and the data is then positioned so that the next record just the right time happened a read head. This principle has been applied as an interleaving and later on hard drives - but there as a fixed factor to adjust the data rate to the processing speed of the computer.
Programming
A computer with drum memory was programmed because of the high access times using a memory map, which was created as a matrix of all present on the drum storage elements. In the instruction code address of the drum of the machine instruction to be executed subsequently was shown to reach the next machine instruction as early as possible according to the determined a table of the command execution time durations. This computer near tedious programming has already been replaced circa 1965 with the development of hardware through the use of advanced programming languages such as Algol 60.
Performance
Typical average power values of drum storage systems:
- Average access time: 10 ms
- Average data rate 10 Mbit / s
- Typical capacity: 10 Mb