Why are external HDD enclosures advertised as 3.5"

Kenneth Burgener kenneth at mail1.ttak.org
Tue Feb 6 10:20:14 MST 2007

Stuart Jansen wrote:
> On Tue, 2007-02-06 at 09:54 -0700, Kenneth Burgener wrote:
>> I was looking for a simple external HDD enclosure and I couldn't
>> remember, off the top of my head, if my standard desktop hard drive was
>> the 2.5" or 3.5" size.  So I pulled out the ruler, and measured the
>> drive.  It is roughly 5.5" x 4" x 1".  It would seem to me that the 3.5"
>> size is what I am looking for, but the drive is not 3.5" wide.  Why?
> It sounds like you actually need a 5.5" enclosure. Desktop systems
> usually use 5.5" drive because they're faster and cheaper. Most laptops
> use 3.5" drives because even though they're slower and more expensive,
> they're smaller. Really small laptops use 2.5" drives. I surprised you
> only found 3.5" and 2.5" enclosures. The good news is that 5.5"
> enclosures are usually much cheaper than 3.5" enclosures.

Really?  I went to Newegg.com and visited their external enclosures
category. (http://tinyurl.com/yr4wy7)  Almost ALL of their enclosures
were the 3.5" and a few were 2.5" (which is why I assumed the 3.5" is
what I wanted).  I did scroll further and found the 5.25" enclosures,
but these were most commonly reported as being for CD-ROM size.

Sites such as this http://tinyurl.com/ysqmed report "This aluminum 3.5"
USB 2.0 hard drive case allows you to easily use your desktop hard drive
as an external hard drive."

This 3.5" enclosure http://tinyurl.com/u429r reports that it's
dimensions are 8.86" x 4.72" x 1.5" which should be more than adequate
to hold the dimensions of my drive.

Which brings me back to why would a labeled 3.5" enclosure hold a 4"
drive? I wonder if it was a marketing blunder that has propagated, or
maybe 3.5" is referring to the actual metal disc inside the HDD.  But if
that were the case then calling a 5.25" enclosure for CD-ROM drives
seems silly since the CD-ROMs are 4.5".

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