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Hard Disk Drives: 3.5" or 2.5"?
(The 2.5" Dilemma)
September 18, 2005
Hard Disk Drives: 3.5" or 2.5"? (Part 1) | Hard Disk Drives: 3.5" or 2.5"? (Part 2)


2.5" (9.5mm) hard drives have been slowly increasing in demand over the past few years. Prices usually push the consumer into a buying decision, but there are many other factors which have contributed to the desire for 2.5" computer systems. First, let's take a look at some of the myths that 2.5" drives have associated with them verus their 3.5" sizes, and include a few not-so-mythic factors.

The Myth Of The 3.5" vs. 2.5" HDD

2.5" drives are smaller, making the data information more susceptible to failure.

Not true. While it is true that initial production of 2.5" drives were problematic, so were 3.5" drives when they were initially released. Remember the IBM RAMAC series? Many of you probably do not. This was the first "hard disk" system. In 1959, we had 50 disks, each 24" in diameter, continuously spinning at a speed of 1200RPM, capable of storing 6MB of data (a staggering 12MB if your company opted for the double-capacity versions). The size of this thing? 400-sq ft space required, and only 6,200lbs.

Just imagine those back in the early 60's, being told by yours truly that someday a 3.5" diameter hard disk, weighing less than a few pounds, would be supporting 300GB, and rotating at speeds of 7200RPM...and being housed in an enclosure no bigger than a cigar box.

Back in the 60's I would have probably been called a Communitst, a spy, and even a witch, and put on trial. At the least, I'd be in a psychiatric facility in an arm-less jacket, dictating articles to my nurse to be posted on websites.

I'm kidding. Ok, let's look at some of the myths...

3.5" drives are faster than 2.5" drives.

Depends.

As long as the Data Density and the Spindle Speed are the same, then yes, a 3.5" drive will probably out-perform a 2.5" drive. Why? It's due to the physical size of the drive itself, and we'll talk more about it in the next few sentences. Even with all things being equal, there is no guarantee a 3.5" drive will perform better. But it is possible--just like it's possible a 2.5" will perform better.

We have a term called Sustained Data Transfer Rate (aka, STR). This rate is most often used in reviews of hard drives, and while I don't see a problem with using this figure in reviews as one of the many specs, I frown on people who use this figure as the exclusive overriding factor of a review. It can be very misleading. It's kind of like using the spec of the tires of a car, to indicate how the car takes a corner. It's just rather simplistic to say that better tires make for better cornering. The driver of the car (in our case the software of the computer) also needs to factor into the cornering performance. The engine of the car (in our case the processor, motherboard, RAM, etc.) also plays a part.

And now let's add another fact. Areas on the outer part of the hard disk read faster than the inner areas of the disk. When you factor in all of these variables, STR doesn't seem too reliable, does it. There are so many variables which dictate and determine a spinning hard drive, moving thousands of revolutions per minute, there's just not an easy way of guaranteeing to the end user, a particular spec rating is going to be consistent.

3.5" drives are more reliable than 2.5" drives.

Not true. All things being equal (for example assuming both drives have no defects) 2.5" drives generate less heat than a 3.5" drive. It's simple physics. The drives are smaller, smaller moving parts, which leads to less heat build-up. The less heat a drive experiences, the longer its life will be. Obviously, this is assuming the drive had no defects originally. Worse-case scenario, 2.5" drives will last just as long as a 3.5" drive.

There are more accessories for 3.5" drives than 2.5" drives.

True. Currently, there are not a lot of options to create an actual 2.5" computer per se, but this is slowly changing. 3.5-to-2.5 IDE adapters are available for those who want to go ahead and use their existing case. We are seeing smaller For external applications however, there are several different types of enclosures for 2.5" drives which can be run via a USB2.0 or an IEEE 1394 connection.

3.5" drives are less expensive than 2.5" drives.

As of the date of this article, this is true. A 120GB 3.5" drive will run you about $70 with rebate, and a 120GB 2.5" drive will cost over $200. These are not cheap. However, you need to ask yourself, do you really need a 120GB hard drive. For some people, they will unequivically say yes, while you may not be so certain. An 80GB or even a 60GB drive, purchased in pairs, might be the better option. In addition, the RPM ratings of the lower capacity drives, will be higher.

In the next section of Hard Disk Drives: 3.5" or 2.5"?, we will discuss advantages of having a 2.5" system.


Sources:

1) Fortune City
2) IBM
3) http://ed-thelen.org


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