HGST HCS5C3232SLA380 User Manual

 

HITACHI CinemaStar 5K 320 Hard Disk Drive specification (Rev 1.21) 

8 

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. 

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. 

 

(Drive is in quiescent state)

 

(ms) 

command (ms) 

Read (Cache not hit) (from Command Write to Seek Start)

 

0.5

 

0.5

 

Read (Cache hit) (from Command Write to DRQ)

 

0.1

 

0.2

 

Write (from Command Write to DRQ)

 

0.015

 

0.2

 

Seek (from Command Write to Seek Start)

 

0.5

 

not applicable

 

 

Table 4    Command overhead