Performance Characteristics; Table 4 Command Overhead - Hitachi CinemaStar P7K500 Specifications

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.
4.5.1 Command overhead
Command overhead is defined as the time required
from the time the command is written into the command register by a host
to the assertion of DRQ for the first data byte of a READ command when the requested data is not
in the buffer
excluding Physical seek time and Latency
The table below gives average command overhead.
Command type (Drive is in quiescent state)
Read (Cache not hit) (from Command Write to Seek Start)
Read (Cache hit) (from Command Write to DRQ)
Write (from Command Write to DRQ)
Seek (from Command Write to Seek Start)

Table 4 Command overhead

HITACHI Deskstar & CinemaStar P7K500 Hard Disk Drive specification (Rev 1.1)
Time (Typical)
(ms)
0.5
0.1
0.015
0.5
10
Time (Typical)
for NCQ
command (ms)*
0.5
0.2
0.2
not applicable
* SATA only