What is defragmentation for?

Muz said:

What is defragmentation for and does it boost something in the hard drive?

Defragmentation - Wikipedia

Defragmentation is advantageous and relevant to file systems on electromechanical disk drives (hard disk drives, floppy disk drives and optical disk media). The movement of the hard drive's read/write heads over different areas of the disk when accessing fragmented files is slower, compared to accessing the entire contents of a non-fragmented file sequentially without moving the read/write heads to seek other fragments.

It moves bits of scattered files together into big blocks [64MB or greater] so that you do not have to spend so much time waiting for its mechanics to jump around the hard disk as you read the file.

Windows does not attempt to write files as single blocks so bits of files get scattered around hard drives as they are written because Windows just uses up space as it finds it.

Since Windows Vista & 7, Windows defragmentation has not bothered moving around blocks of 64MB or greater. So your files can remain fragmented to that extent. MS experimented and decided that its old practice of fully defragmenting files gained no benefit once lumps of 64MB were consolidated. If I thought there was any reason to expect you to be interested in their explanation, I would post a link to
Disk Defragmentation – Background and Engineering the Windows 7 Improvements - Microsoft Docs

Note that if Windows recognises a drive as an SSD then it normally trims ["re-trims"] SSDs when you run 'Optimise' on a schedule but it does defrag monthly according to defrag - Microsoft Docs under the sub-heading 'Scheduled task'. I have never managed to catch a record of anything other than trimming happening.


Denis

A note about defragging an HDD (hard drive, not SSD). Using the Analyze function first will tell you if there really is a need to Defrag the drive. Defragging itself puts wear and tear on the heads and spindle. Even though all free space may not be together on the hard drive does not always mean there is a need to defrag. The operation of Consolidation attempts to group clusters contiguously, leaving as many large empty clusters/blocks as possible. This may not always be advantageous. If the clusters are moved to the inner cylinders of the drive, and the files are subject to frequent re-writing of changed data, the consolidation will quickly break down, resulting in small blocks written towards the end of the drive, the slower part. This is what produces fragmentation to begin with. If Analyze says "OK", let it be.

An historical note: back in the '90s and days of 120MB, 210MB, 340MB and 540MB HDDs [Yes, MegaByte] it was rather important from the standpoint of performance to run defrag as the drives were somewhat slower and CPUs were getting faster-performing, running a program could be frustrating. Also the deletion of a file didn't change the drive capacity immediately, only erased the first character of a file name and marked that particular space as available for a future data save when needed, defrag could overwrite that "vacant" area which in turn sped up the search for all parts of a file. Of lesser importance was/is the defrag could make it more difficult to recover deleted files, added to security again by overwriting deleted data.

pietcorus2 said:

" back in the '90s "...........modern HDDs are much better nowadays , I think you dont have to defrag them at all anymore .
I wonder what will happen with your OS-backups , after defrag a few times..........

I let Win10 handle its needs, experience shows it much better than Win7 and earlier.

As for backups, the program doing them should take care of housekeeping but any drive is susceptible to the same issues as others, they are electro-mechanical and can fail just as a car or household appliances can. The difference between a backup drive and an in-use drive is the sizes/blocks of data being written at any one time.