Emulex MD21/S2, Technical Manual

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ESDI Overview
2.4 ESDI OVERVIEW
The Enhanced Small Device Interface (ESDI) is a standard interface
established to support multiple disk drives on the same controller.
ESDI was designed to extend the capabilities of the ST506
interface. The following points regarding the MD21 implementation
of the ESDI should be noted:
• The data separator is on the drive (instead of the
controller as in ST506 interfaces)? therefore, NRZ data can
be used between controller and drive.
• The drive, not the controller, provides the reference clock.
• On the data cable, ESDI replicates rotational information
from the control cable so that each drive position can be
monitored radially. This capability increases performance in
multiple-disk configurations.
• ESDI supports higher data transfer rates.
A typical multi-drive ESDI configuration is shown in Figure 2-4.
M D 2 1 0 3 -0 9 9 0
Figure 2-4. Typical Multi-Drive Configuration
2-8 General Description