IBM DDRS-39130 - Ultrastar 9.1 GB Hard Drive

3.4.1 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
Figure 3. Command Overhead
3.4.2 Mechanical Positioning
3.4.2.1 Average Seek Time (Including Settling)
“Typical” and “Max” are given throughout the performance specification by;
Typical Average of the drive population tested at nominal environmental and voltage conditions.
Max Maximum value measured on any one drive over the full range of the environmental and
voltage conditions. (See 6.4, “Environment” on page 39 and 6.6, “DC Power
Requirements” on page 41 for ranges.)
The seek time is measured from the start of actuator's motion to the start of a reliable read or write opera-
tion. Reliable read or write implies that error correction/recovery is not used to correct arrival problems.
The average seek time is measured as the weighted average of all possible seek combinations.
Weighted Average =
∑
max
n =1
( max + 1 − n)(Tn.in + Tn.out)
( max + 1) ( max)
Where:
max = Maximum seek length
n = Seek length (1 to max)
Tn.in = Inward measured seek time for an n track seek
Tn.out = Outward measured seek time for an n track seek
Read Command Case with 6x64KB buffer (Drive is in quiescence state) Time
Cache Not Hit <0.40msec
Cache Hit <0.03msec
Figure 4. Mechanical Positioning Performance
Command Type Typical Max
Read 7.5 [msec] 8.5 [msec]
Write 8.3 [msec] 9.2 [msec]
Drive Characteristics 11