Hi. I wanted to purchase an internal hard drive and enclosure kit separately and put it together. I have two other external hard drives and they are both 3.5". I was looking for a 2.5" this time but, I wanted to know if this is any different from 3.5" in performance and longevity. I wanted to know if the 2.5" can be left running for as long as the 3.5" because the enclosures for the 2.5" are much smaller with no fan and most of the time they don't even have a power outlet. They come with a USB power outlet that connects to your computer and draw power from that. It recharges as well. But the battery life is very low. This was my main concern actually. I know I have left the 3.5" hard drives running for a long time. But, with the 2.5" enclosures, can I plug the power source to the USB of the computer and leave it running for a long time? Can it last, without overheating, as long as a 3.5" hard drive and can it be left running as long and be trusted not to delete data when drawing power from the computer like the 3.5" can be left running plugged into an outlet powersource? Thanks for your help in advance. I greatly appreciate it.

Given the choice, go for 3.5" because 2.5" run slower (5,400rpm if I recall) and, as you point out, they often rely on USB for power. I would only choose 2.5" for portability on a laptop, for general workhorse externals then 3.5" are better. As far as longevity is concerned I haven't yet come across a totally reliable external drive - I'm currently in 'conversation' with Freecom over a couple of backup drives which only lasted 2 years of fairly continual use before collapsing - unfortunately my client was using one of them as an overflow drive rather than a backup so his data was put at risk - his own fault, I know, but not what you'd expect from a branded drive. "I know that I'm mad, I've always been mad"

The 2.5" enclosures are for laptop harddrives. heat should not be an issue as those drives are meant to work in confined spaces. As for running for long periods of time, I don't see why there would be more of an issue than with the 3.5" drives. Michael J

I don't understand why you are even thinking about a 2.5" drive for a desktop. There's no reason that I know of to consider it. Stick with the 3.5". Do yourself a favor BACKUP!

I have several 3.5 inch USB external HDDs. I was using a 1 GB memory stick to move files from work to home and back and found the read/write to be slow and the 1 GB to be limiting but it was much easier than packing up and moving 3.5 inch HDDs and their power supplies around. I put together a 5400 RPM 40GB 2.5 inch external HDD and it runs much faster than the memory stick (though not as fast as the 3.5 inch HDDs) and I don't have to pack a power supply and it fits in my shirt pocket.