Interleave

Interleave

A low-level formatting tool running tests to find the highest performance interleave choice for a 10-megabyte IBM PC XT hard drive.

Sector interleave is a mostly obsolete device characteristic related to access time, dating back to when computers were too slow to be able to read large continuous streams of data. Interleaving introduced gaps between data sectors to allow time for slow equipment to get ready to read the next block of data. Without interleaving, the next logical sector would arrive at the read/write head before the equipment was ready, requiring the system to wait for another complete disk revolution before reading could be performed.
However, because interleaving introduces intentional physical delays into the drive mechanism, setting the interleave to a ratio higher than required causes unnecessary delays for equipment that has the performance needed to read sectors more quickly. The interleaving ratio was therefore usually chosen by the end-user to suit their particular computer system's performance capabilities when the drive was first installed in their system.
Modern technology is capable of reading data as fast as it can be obtained from the spinning platters, so hard drives usually have a fixed sector interleave ratio of 1:1, which is effectively no interleaving being used.

[edit] Seek time

Average seek time ranges from 3 ms^[72] for high-end server drives, to 15 ms for mobile drives, with the most common mobile drives at about 12 ms^[73] and the most common desktop type typically being around 9 ms. The first HDD had an average seek time of about 600 ms and by the middle 1970s HDDs were available with seek times of about 25 ms. Some early PC drives used a stepper motor to move the heads, and as a result had seek times as slow as 80–120 ms, but this was quickly improved by voice coil type actuation in the 1980s, reducing seek times to around 20 ms. Seek time has continued to improve slowly over time.
Some desktop and laptop computer systems allow the user to make a tradeoff between seek performance and drive noise. Faster seek rates typically require more energy usage to quickly move the heads across the platter, causing loud noises from the pivot bearing and greater device vibrations as the heads are rapidly accelerated during the start of the seek motion and decelerated at the end of the seek motion. Quiet operation reduces movement speed and acceleration rates, but at a cost of reduced seek performance.