User guide

Galaxy 55 User Guide
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Hot swap Hot swapping is the term used for manually swapping a failed disk unit with a replacement while the
Galaxy 55 subsystem is in normal use.
Hz (Hertz) a frequency measurement unit used internationally to indicate cycles per second.
Initialize To prepare a hardware device for use.
LED Light Emitting Diode. A small light displayed on the cabinet, disk units and power supply units.
LRC Loop Resiliency Circuit: Circuits within the I/O modules which provide loop resiliency in the event of a
drive failing or being unplugged.
LRC I/O module A plug-in module used to connect the internal FC-AL channels from the Galaxy 55 backplane
to the rear of the enclosure.
Module (power supply, drive, ESI/Ops, I/O) A module is a power supply, disk drive or electronics unit held
in a carrier that plugs into a bay inside the enclosure. A Galaxy 55 enclosure can contain twelve drive modules and
three power supply/cooling modules, an ESI/Operating Panel module and two LRC I/O modules.
Operating system The software running the host computer. For example, on PCs it is often Windows 95,
Windows NT or OS/2 and on Hewlett-Packard machines it could be HP-UX.
Parallel Transmission The transfer of data characters using parallel electrical paths for each bit of the
character, for example, 8 paths for 8-bit characters. Data is stored in computers in parallel form, but may be
converted to serial form for certain operations. See Serial Transmission.
Power Cord Throughout this Galaxy 55 user guide this term is used in accordance with the preferred US context
of: “an insulated flexible electric wire fitted with connectors at each end and used for the transmission of electrical
power to computer equipment.
Protocol A system of rules and procedures governing communications between two or more devices. Protocols
vary, but communicating devices must follow the same protocol in order to exchange data. The format of the data,
readiness to receive or send, error detection and error correction are some of the operations that may be defined in
protocols.
Redundant Not essential.
Serial Transmission The transfer of data characters one bit at a time, sequentially, using a single electrical path.
See Parallel Transmission.
Trifurcated (power cord) Throughout this user guide, the term is used as the UK equivalent of the US term
furcated.
A trifurcated power cord is a three branched cord joined together by a yoke.