Drum Organization for Strobe Addressing

In strobe addressing, a pulse from the memory drum or disk forces the control unit to accept a program word. Strobe addressing for drums or disks costs less than 20 per cent of conventional addressing for real-time control programs, but becomes impractical for very complex problems. A comparison of various forms of strobe and conventional addressing shows that simple strobe addressing uses the memory as efficiently as conventional addressing if the problem can and must be solved in one revolution. By interlacing instructions with complete freedom for the program to switch interlaces, a strobe-addressed drum appears to have as many parallel bands as it has interlaces, thereby extending the advantages of strobe-addressing to more complex problems. Only minor changes in the program memory are necessary, and the arithmetic element and control unit remain essentially unchanged. The irregular interlace organization is described for an airborne computer with an 8-fold interlace, and its effectiveness is evaluated. In a test problem, this method reduces the size of the required memory by a factor of four and increases the effective computing speed fourfold.