Abstract :
Concurrent peripheral transfers are normally necessary to match the power of modern computers. Associated with each peripheral device is a control word, or words, which specifies the current operation. During a transfer operation, the word is updated after a transfer of information to or from the associated peripheral device. Further information in a control word may be used to determine the end of a transfer or other operation. In about the middle of 1963, it was realised that no information was transferred during many of the stages needed to make up a magnetic-tape transfer operation. Thus, control information passed down the existing interconnections between the computer and the tape units during these stages need not increase the peak demand on the computer. Moreover, the operations necessary during these stages could be carried out economically, using a single central unit which is time-shared among a number of concurrently operating tape units. The transfer-address and-terminating information need only be stored in a control word while information is actually being transferred; at other times during a magnetic-tape transfer operation, it can be used to store information required by the central control unit to provide further time-shared-control features. It is shown that this control information can be collected from a store of constants at the beginning of each stage. The only additional information required in each control word is the number denoting the stage reached during a transfer operation. The advantages of this system are as follows: (a) Many of the operations performed during the control stages can use the central unit already used to control the transfer and termination of information, with a few added features, where an almost comparable unit was formerly needed for every concurrently transferring magnetic-tape unit. (b) Storage formerly required in a tape-control unit can, with greater economy, be stored in the associated control word. To allow t- he existing interconnections to be used during the control stages requires an insignificant addition to each tape-control unit.
