digitaldingus Article

Hard Disk Drives: 3.5" or 2.5"?
(The 2.5" Dilemma)

September 18, 2005


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.


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.

Part 2 (September 18, 2005)

Since we've dispelled a few myths, let's discuss how a 2.5" system might benefit you.

2.5" Drives: The Benefits

Small Spaces

I currently have 4-3.5" hard drives in my computer. Hopefully I didn't make you fall out of your chair. I don't have a RAID setup (don't worry about that term if you don't know what it is). All I have are 4 independently operating drives. The computer case I have is a full tower, 24" (H) x 18" (D) x 8" (W). Even with this size of a case, the insides are not ideal. I have cables going all over the place, nesting not too far from the hard drives. The heat build-up is a problem at times, especially in the summer months. Since I have 4-80mm fans running, in addition to 2 processor fans going, the case stays relatively cool. However, the noise generated is definitely noticeable if I'm away from home for an extended period of time then come back. In fact, many friends who come over to visit mention how loud my computer is. Most of the noise is generated by the fans pulling air into and pushing it out of the computer case.

Due to the size of a 2.5" drive, four 2.5" disks can be stacked in a space that one 3.5" drive occupies. Now, this is something to think about. The reason why computer cases are so large, is partially due to the option of putting several drives in it. Many computer users today have two drives. The number of "Two-Drive" owners is increasing mostly because of the inexpensive prices of the drives themselves. If you do some smart shopping, you'll end up with a very nice rebate. From time to time I do some searching on the net for some great bargains, and present those deals to DigitalDingus website viewers, so this is another option for you. Just imagine how much space you could save if you only had two 80GB 2.5" hard drives.

2.5" Form Factor Is Pretty Fast

For some people, having the fastest drive is required. PC Gaming enthusiasts are loading their games on 10,000RPM drives along with $500 video cards and so forth without a second thought. There are 2.5" drives reaching the 10,000RPM mark, but they cost around $800USD. So currently, a very fast 2.5" HDD is out of reach for most consumers. For commercial interests, 2.5" form factor drives are becoming more of an option. What you have to ask yourself, is how fast is "fast" to you. I've tested 5400RPM drives and I was very impressed with the speed ratings and real-life performance with running appplications. Yes, you can read reviews on how fast a drive performs till you get a headache. However, I'm still a little hesitant to judge a drive based on millisecond differences, especially when so much of a drive's performance is regulated by the software application, browser, plugins, and so on.

Less Heat

2.5" hard drives do not give off as much heat as a 3.5" drive. They are also much less noisy. I can say this definitively, because I've personally reviewed a few 2.5" drives myself. I highly recommend Fujitsu drives because they've been in the business of pioneering small form factor storage systems and in my opinion, are paving the way towards smaller computer systems for the common user. Few companies are trying to make 2.5" drives as fast and common as 3.5" like Fujitsu is.

Low Power Requirements

2.5" drives also have much less power consumption, and it's common for a 2.5" drive to run on only 10% of what a 3.5" drive requires. This is very important, as a higher power consumption, translates into a higher chance of failure. Unfortunately, the more power current you have flowing through a particular device, the more chance for error. And when we're talking about computer components which are the most sensitive to electrical currents, the importance of low power consumption becomes clear.

2.5" Might Be For You

If you're not too concerned about having the fastest hard drive on the planet, but are more interested in finding a way to create a low heat, low power, and smaller space requirement computer system, the 2.5" form factor just might be for you.

In the future, more articles which deal specifically with building 2.5" systems will be featured. Be sure to make DigitalDingus articles a part of your normal surfing routine.


1) Fortune City
2) IBM


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