The Agilent/HP 3499 Series Switch/Control System is a modular, high‑density switching and control chassis designed for automated test applications. Available in three frame sizes—3499A (five plug-in slots), 3499B (two slots), and 3499C (nine slots)—it supports a wide variety of plug-in modules, including RF multiplexers, general-purpose relays, matrix switches, and digital I/O. Designed for both bench and rack-mounted operation, each mainframe offers flexible control via GPIB or RS‑232, with a built-in 4-bit digital I/O port and optional SCPI command support.