IBM IC35L040AVVN07-0 Hard Drive Specifications - Page 27

Performance characteristics

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4.4 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. 4.4.1 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) Time (Typical) (ms) 0.3 0.1 0.015 0.3 Time (Typical) for queued command (ms) 0.3 0.1 0.05 not applicable Figure 4. Command overhead 4.4.2 Mechanical positioning 4.4.2.1 Average seek time (without command overhead, including settling) Command Type Read (60 GB - 120 GB models) Read (20 GB & 40 GB models) Write Read (Quiet Seek mode) Write (Quiet Seek mode) Typical (ms) 8.2 8.5 9.2 19.5 20.5 Figure 5. Mechanical positioning performance Max (ms) 9.2 9.5 10.2 20.5 21.5 Deskstar 120GXP hard disk drive specifications 13

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4.4 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.
4.4.1 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.
not applicable
0.3
Seek (from Command Write to Seek Start)
0.05
0.015
Write (from Command Write to DRQ)
0.1
0.1
Read (Cache hit) (from Command Write to DRQ)
0.3
0.3
Read (Cache not hit) (from Command Write to Seek Start)
Time (Typical) for
queued command
(ms)
Time (Typical)
(ms)
Command type
(Drive is in quiescent state)
Figure 4. Command overhead
4.4.2 Mechanical positioning
4.4.2.1
Average seek time (without command overhead, including settling)
21.5
20.5
Write (Quiet Seek mode)
20.5
19.5
Read (Quiet Seek mode)
10.2
9.2
Write
9.5
8.5
Read (20 GB & 40 GB models)
9.2
8.2
Read (60 GB – 120 GB models)
Max
(ms)
Typical
(ms)
Command Type
Figure 5. Mechanical positioning performance
Deskstar 120GXP hard disk drive specifications
13