Approaching real-time: digital disk recorder and workstation interchange of video streams

A conventional video digital disk recorder (DDR) interfaces to graphics workstations and other computer systems through standard input/output ports such as Ethernet and SCSI. These I/O options are adequate for transferring CCIR-601 uncompressed images at rates ranging from a fraction to only a few images per second. Due to the bandwidth limitations of Ethernet and SCSI, interchange of real-time video streams can only be achieved with highly compressed video signals. In order to obtain the data rates necessary for delivering uncompressed CCIR-601 video to the workstation, the external device can be interfaced directly to the internal bus of the computer system. A good example of such a high-speed internal bus architecture is provided by the Graphics I/O (GIO) bus in desktop Silicon Graphics Workstations. The GIO bus has a bandwidth of 132 MBytes/sec with sustained data rates that allow the operating system to transfer full bandwidth digital video to internal memory/graphics subsystems. The present article describes the interface of a DDR to the GIO bus, and the associated issues that arise when the video peripheral device is no longer the bottleneck in delivering a high quality video stream to computer graphics application programs