The lowest cost secondary storage option, SCSI disks may be utilized in either the removable4.6.2 IP12
or the SCSI box inserts for the lower cabinet.
SCSI disks are available as half-height drives with 380MB of storage space, or as full-height
drives with either 780MB, 1.2GB, or 1.6GB of available storage.
Certain applications require storage of massive databases which must then be reaccessed
rapidly. These include image analysis, C3I, database development, and mission rehearsal over
large photo-realistically rendered terrain. In these and other cases, it is important to have fast
disks to enable the rapid transfer of data to and from secondary storage or archives. For
SkyWriter, SGI supports the Intelligent Peripheral Interface or IPI2 disk drives.
These 1.1GB drives are interfaced via a controller card which is placed in one of the four free
9U VME slots. Each controller has two channels, each of which has a bandwidth of 10MB/sec
with a peak transfer rate of 6MB/sec. Each channel is also capable of supporting up to eight
separate drives. Two controllers can be utilized in each system to support a maximum of four
independent IP12 channels, thus up to four IP12 drives may be striped for peak throughput of