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SCSI
(Small Computer System Interface)
This document describe SCSI parallel connectors.

Interface information
Bus width

Width External Connector
Narrow
(8bit) 		DB25 DB25
LD50 LD50
HD50 HD50
Wide
(16bit) 		2*HD50 2*HD50
2*HD50
HD68 HD68
Wide32
(32bit) 		2*HD68 2*HD68
2*HD68
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SCA Internal Connector
HE50 / HE50
HD68 SCA80 HD68
2*HD68 / 2*HD68
2*HD68
Note: There are also Serial SCSI Interfaces, IEEE-1394.
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Adaptec decided to associate a color with each external SCSI connector, here is a list of these :
External connector Adaptec Color Code
DB25 DB
25-pin 		White
DB50hd DHD
50-pin 		Orange
DB68hd DHD
68-pin 		Red
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Bus Speed
Speed Frequency Narrow speed Wide speed
SCSI ? 5MHz 1,5 to 5 MB/s / [no wide device]
Fast SCSI 10MHz 10 MB/s 20 MB/s
Ultra SCSI 20MHz 20 MB/s 40 MB/s
Ultra2 SCSI 40MHz 40 MB/s 80 MB/s
Ultra 160/m ? 80MHz / [no narrow device] 160 MB/s
Note: "Ultra 160/m" is not a SCSI standard yet, it's Adaptec version of the upcoming Ultra3 standard.
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  • Narrow external (LD50 & HD50)

    LD50 is SCSI-1 standard and is still used for many narrow (formerly called 8bit SCSI) devices.
    Consider using the HD50 for new designs. HD50 is SCSI-2 standard, fully compatible with LD50, support higher frequency such as UltraSCSI and is smaller.

  • Narrow internal (HE50)

    Internal Narrow SCSI cable, similar to external LD50 and HD50.

    • WIDE
  • Wide external (HD68)

    This connector is used for external Wide devices.
    For 8bit devices, the HD50 should be used instead.

    • Wide internal (HD68)

    This connector is used for internal Wide devices, for 8bit devices, the HE50 should be used instead.

    WIDE 32
  • Wide32 external (Dual HD68)

    ?
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