files. Defragmentation is a procedure used to minimize delay in retrieving data by moving related items to physically proximate areas on the disk. Some computer operating systems perform defragmentation automatically. Although automatic defragmentation is intended to reduce access delays, the procedure can slow response when performed while the computer is in use. Effect of areal density HDD data transfer rate depends upon the rotational speed of the disks and the data recording density. Because heat and vibration limit rotational speed, increasing density has become the main method to improve sequential transfer rates. Areal density'' (the number of bits that can be stored in a certain area of the disk) has been increased over time by increasing both the number of tracks across the disk, and the number of sectors per track. The latter will increase the data transfer rate for a given RPM speed. Improvement of data transfer rate performance is correlated to the areal density only by increasing a track's linear surface bit density (sectors per track). Simply increasing the number of tracks on a disk can affect seek times but not gross transfer rates. According to industry observers and analysts for 2011 to 2016, “The current roadmap predicts no more than a 20%/yr improvement in bit density”. Seek times have not kept up with throughput increases, which themselves have not kept up with growth in bit density and storage capacity. Interleave Sector interleave is a mostly obsolete device characteristic related to data rate, 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 between blocks of data thereby lowering the data rate, 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