9
Western Digital Hard Disk Drive OEM Specification
4.5
Performance Characteristics
Drive performance is characterized by the following parameters:
Command overhead
Mechanical positioning
-
Seek time
-
Latency
Data transfer speed
Buffering operation (Look ahead/Write cache)
All the above parameters contribute to drive performance. There are other parameters that contribute to the
performance of the actual system. This specification defines the characteristics of the drive, not the characteristics of
the system throughput which depends on the system and the application.
The terms “Typical” and “Max” are used throughout this specification with the following meanings:
Typical
The average of the drive population tested at nominal environmental and voltage conditions.
Max
The
maximum value measured on any one drive over the full range of the environmental and voltage
conditions. (See Section 6.2, “Environment” and Section 6.3, “DC Power Requirements”)
4.5.1
Mechanical Positioning
4.5.1.1
Average Seek Time (without command overhead, including
settling)
Command Type
Typical (ms)
Max (ms)
Read
7.4
10.0
Write
8.2
11.0
Table 5 Average Seek Time
4.5.1.2
Single Track Seek Time (without command overhead,
including settling)
Common to all models and all seek modes
Function
Typical (ms)
Max (ms)
Read
0.23
0.25
Write
0.32
0.45
Table 6 Single Track Seek Time
4.5.1.3
Average Latency
Rotational Speed
Time for a Revolution
(ms)
Average Latency
(ms)
7200 RPM
8.33
4.16
Table 7 Latency Time
