Editing Serial Storage Architecture (section)

==Link characteristics==
All the components in a typical SSA subsystem are connected by bi-directional cabling. Data sent from the adaptor can travel in either direction around the loop to its destination. SSA detects interruptions in the loop and automatically reconfigures the system to help maintain connection while a link is restored.

Up to 192 [[hot swap]]pable hard disk drives can be supported per system. Drives can be designated for use by an array in the event of hardware failure. Up to 32 separate [[redundant array of independent disks|RAID]] arrays can be supported per adaptor, and arrays can be mirrored across servers to provide cost-effective protection for critical applications. Arrays are connected by thin and inexpensive copper cables situated up to 25&nbsp;metres apart, allowing subsystems to be located in secure, convenient locations, far from the server itself.

The copper cables used in SSA configurations are round bundles of two or four twisted pairs, up to 25 metres long and terminated with 9-pin [[D-subminiature|micro-D]] connectors. Impedances are 75&nbsp;[[Ohm (unit)|ohm]] single-ended, and 150&nbsp;ohm differential. For longer-distance connections, it is possible to use [[fiber-optic]] cables up to 10&nbsp;km (6&nbsp;mi) in length. Signals are [[differential TTL]]. The transmission capacity is 20&nbsp;[[megabyte]]s per second in each direction per channel, with up to two channels per cable. The transport layer protocol is [[non-return-to-zero]], with [[8B/10B encoding]] (10&nbsp;bits per character). Higher protocol layers were based on the [[SCSI]]-3 standard.