How is 3.5'' and 2.5'' measured on the hard drive?

[vtohthree]

I've never bothered to actually measure the hard drives dimensions before, and stumbled upon this:

http://accessories.us.dell.com/sna/Prod...RPU=&page=dellpartsproductlisting.aspx

2.76'' ...So I'm assuming that 2.5'' and 3.5'' comes from the actual platter sizes inside the Hard drive...probably the diameter?

 

[SparkyJJO]

Drives were originally measured by the disk size. For instance, a 5.25" floppy (old stuff) is that size. The drive itself is almost 6" but they were measuring the floppy. Same with 3.5" floppies. When those went out the name for the bays just kinda stuck, even though its technically wrong.

 

[bendixG15]

Drives still are measured by disk diameter..technically that is correct.

 

[corkyg]

Originally posted by: bendixG15
Drives still are measured by disk diameter..technically that is correct.

:thumbsup: Correct! I have about 6 2.5" drives in my parts drawer - and the actual width is nominally 2.75" and the length is 3.75" not counting the pins. Thickness varies from about 9 to 12 mm. I have about a dozen 3.5" drives, and they measure nominally 4" x 5.75" x 1". Drives are sized by their disks - not their cases.

 

[Zepper]

Hard drive dimensions are that way because they fit in the same width bay as a 5.25" floppy drive or a 3.5" floppy drive (don't know where the 2.5" measure came from for the notebook drives). And the FDs got their dimensions as posted above (actual diameter of the media inside the cover - the mylar). Anyone else here old enough to have hands-on with the "original" 8" floppy disk?

.bh.