Much like the laser in a CD player (or the needle on a record player), the disk spins underneath while the head moves in and out to locate the proper “track” that contains the next chunk of the file being accessed. There’s a physical read/write head that moves around on the media when data is being accessed. You normally never see this, because the file system – that “NTFS” or “FAT32” thing you may see referenced from time to time – takes care of locating all those chunks when you read or write a file. That means a file could have its contents spread out randomly over a hard disk’s physical surface.

Files are stored in pieces – frequently in 512 byte “chunks” which may or may not actually be physically next to or even near each other. Traditional hard disks are rotating disks of magnetic material with a read/write head that has to move around to find the data. In my opinion, you should never defragment a drive based on solid state memory. You’ve hit one nail squarely on the head: flash devices and SSDs don’t gain significant performance benefit from being defragmented.

Defrag memory windows 10