Method for Copying Data Without Actually Moving Any of the Data in Main Memory
Original Publication Date: 1988-Jun-01
Included in the Prior Art Database: 2005-Feb-15
This method utilizes a pair of buffers in ping-pong or overlapped I/O mode. That is, while one buffer is inputting data, the other buffer is outputting data. In this method, data (and the count field immediately preceding the data) is first read from the input device to a buffer (buffer A). Next, any prefixes to the data that must be changed for the data to be written directly to an output device are changed. As an example, in an IBM MVS environment, there is an 8-byte count field before a block of data that must be changed to reflect the fact that the data is being written to a different secondary storage device. After this, the data in buffer A is written to the output device. At the same time, data is read into buffer B from the input device.