Simple Expanders Extend SCSI Bus Reach into the Future (PDF)
A white paper by David Rotman of Compaq Computer Corp. and Harry Mason of LSI Logic discussing how simple expanders (versus bridging expanders) allow for a significant increase in overall attainable SCSI bus length and SCSI domain diameter.

SCSI expanders are active interconnect components that logically connect and physically isolate segments of a SCSI domain. In addition to isolating segments, expanders allow for a significant increase in overall attainable SCSI bus length and SCSI domain diameter. SCSI expanders are available in two basic types, simple and bridging. For the purpose of this summary, we will largely concentrate on simple expanders. Simple expanders available today do not consume a SCSI ID and are capable of handling Single-ended (SE), and/or one of two modes of differential (Diff), Low Voltage Differential (LVD) or High Voltage Differential (HVD) SCSI transmission on either side.