To provide the interactive imaging capabilities discussed above, the imaging
hardware must provide certain minimum levels of performance.
Figure 18.5 schematically represents data flowing from the trace
manager to the computational processes and the image generated there being
sent to the display manager for eventual display on the monitor. To perform
the interactive focusing discussed above, the computational engine must
deliver approximately 200 to 
. While this number may be difficult
and expensive to obtain in a single-processor system, it is easily obtainable
in parallel systems. Likewise, in order to satisfy the demands of
interactive stacking, the trace manager is required to deliver many thousands
of traces per second (approximately 4 to 8 Kbytes/trace) to the computational
processes. Since these traces are essentially randomly ordered throughout a
multigigabyte data volume, a simple calculation will show that, for current
disk drive technology, the limiting factor in supplying the data is the disk
seek time, not the aggregate transfer rate. Again, a solution to the problem
is for a number of disks working in parallel to provide the needed
performance. Finally, in order to display movies of seismic gathers at eight
frames per second, the graphics processors must be able to absorb and display
eight megabytes of data per second. Once again, this requirement may be
satisfied by multiple nodes working in parallel.
In addition to the general performance issues, which could be achieved by the creation of a specially built machine, or the addition of custom I/O devices to an existing supercomputer, we chose to use only commercially available hardware. The reasons for this choice are twofold: We wanted other interested researchers to be able to duplicate our efforts, and we wanted the system to be reasonably affordable.