Specifications

4.5 Performance characteristics

The performance of a drive is characterized by the following parameters:

! Command overhead

! Mechanical head positioning

- Seek time

- Latency

! Data transfer speed

! Buffering operation (read ahead/write cache)

NOTE: All the above parameters contribute to drive performance. There are other parameters that contri-

bute to the performance of the actual system. This specification tries to define the bare drive character-

istics, not 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 last byte of command phase

! to the first byte of data phase

! excluding

- Physical seek time

- Latency time

- Initiator delay with reconnections

<30 µs

Cache Hit

<400 µs

Cache Not Hit

TimeRead Command Case (Drive is in quiescent state)

Figure 6. Command overhead

Ultrastar 146Z10 hard disk drive specifications