HP Surestore 125ex - Optical Jukebox Manual page 101

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The SCSI bus is electrically implemented in three ways: single-ended, high-voltage differential, and low-voltage differ-
ential. These terms come from the way the signals are asserted on the bus.
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Single-ended buses use a 5-volt signal that is referenced to ground. This method makes the bus somewhat susceptible to
noise and loss of signal quality over distance. The maximum allowable length of a single-ended SCSI bus was initially
6 meters (19.7 feet). Fast SCSI required the maximum length of the bus to be reduced to 3 metres (9.8 feet).
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High-voltage differential buses uses two lines for each signal and measures the voltage difference between the two sig-
nals. The differential configuration retains more signal quality than single-ended and is not as sensitive to noise, allow-
ing for a longer cable length. The maximum allowable length of a high-voltage differential bus is 25 meters (82 feet) for
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all types of buses (narrow, wide, fast, Fast-20)
Low-voltage differential buses (Ultra 2) use less of a voltage difference between the two signals used for each bus sig-
nal. The low-voltage differential configuration also retains more signal quality than single-ended and is not as sensitive
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to noise as either the single-ended or high-voltage differential buses. The maximum allowable length of a low-voltage
differential bus is 12 metres (39.4 feet).
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ONNECTORS
50-pin connectors - narrow devices only
• 50-pin low-density clip Centronics-type (external)
This is a large connector that is similar to a printer cable. This type of connector is gradually being replaced by the
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