IBM IC35L036UWDY10 Hard Drive Specifications - Page 28

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 contribute to the performance of the actual system. This specification tries to define the bare drive characteristics, 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 Read Command Case (Drive is in quiescent state) Cache Not Hit Cache Hit Figure 6. Command overhead Time