| 摘要 |
PURPOSE:To prevent the increase of the data volume by comparing the number of bytes of true data and that of compressed data with each other to check the actual compression effect and instructing a data compressing means to compress or not compress data. CONSTITUTION:A channel interface data transfer control part 13 receives data from a host CPU 11 through a channel 12 by the indication of data transfer start from an MPU 14 and transfers data to a data compressing mechanism 18, a channel byte counter 17, and a second data buffer 24 and reports this data transfer to the MPU 14. The mechanism 18 subjects data to run length compression or encoding compression and sends compressed data to a first buffer 22 and a device byte counter 23. The MPU 14 compares the number of bytes of true data from the counter 17 and that of compressed data from the counter 23 with each other when receiving the report of the end of data transfer from the control part 13; and when the former is smaller, the mechanism 18 is instructed not to compress data and true data is stored in the buffer 22. When the former is larger, the mechanism 18 is instructed to compress data and compressed data is stored in the buffer 22. |
