Introduction
Average access time:
Average access time = average seek time + average wait (latency) time.
The average access time not only reflects the internal transmission rate of the hard disk, but also is the best standard for evaluating the time it takes for the hard disk to read and write data.
Average latency time (Average latency time):
When the head moves to the track where the data is located, it is the time to wait for the desired data block to continue to rotate under the head. It is 1/2 of the disc rotation period.
Average seek time:
It refers to the time it takes for the hard disk to move the read-write head on the disk to the specified track to find the corresponding target data. It describes the hard disk to read the data The capacity, in milliseconds.
The definition of the average access time: the average length of time spent on the website for each visit.
Calculation method
During the process of the CPU executing a program, the number of accesses to the Cache is 3800, and the number of accesses completed by the main memory is 200. If the access cycle of the Cache is 5ns and the access cycle of the main memory is 25ns, the hit rate of the Cache is 0.95s, and the average access time of the CPU is 6ns.
Related knowledge
The average seek time of the hard disk (Average Seek Time) is actually the average time for the head to move above the specified track, and the corresponding sector on the track will move to The average time under the head, we call it the average latency of the hard disk. Obviously, the seek time and latency here, plus some operation time such as instruction processing, is the time from when the instruction is issued to the hard disk actually starting to read and write operations, which is what we call the average access time (Average Access Time) . In general, the faster the hard disk rotates, the shorter the average latency, which is basically the same as the average latency of the hard disk at 7200rpm (the average latency of a 7200rpm hard disk is about 4.16ms), and the instruction processing and other operations are very short and can be completely ignored (see As the error generated under random circumstances). The average access time of the hard disk can be measured by the test software. You can pay attention to this indicator when looking at the result data. It has an important relationship with the performance of the hard drive