2.5" vs 3.5" at same RPM

just quick question from what i've heard say we have 2 of the same drives say a
Hitachi Travelstar 2.5" 7200RPM 8MB HDD
and a
Hitachi Deskstar 3.5" 7200RPM 8MB HDD


will the 2.5" be faster since its smaller and has a smaller area of rotation?

 

The size pertains to what size bay they fit into, I dont think the speed is affected since they both spin at 7200rpm's. I believe the 3.5" is a desktop HDD, and the 2.5" is the smaller version ment for laptops.

[EDIT] Yeah the name of the 2.5 is "Travelstar" so its for notebooks, and the same with the Deskstar. A 3.5 wont fit in a notebook so get the travelstar. I just pulled my HDD out of my 1210 and its a Hitachi Travelstar 2.5, very small thing.

 

well I know a 2.5" is a notebook and 3.5" is a desktop hdd but i remember someone on forums mentioned that the smaller HDD the 1.8" which you see in ultraportables at 4200rpm werent as bad as a 4200rpm 2.5" because of the smaller size so it had smaller rotation or something.

 

Well I guess logically that something with a smaller radius like a 2.5" or 1.8" HDD would take a little less time and power to get up to speed, but its top speed wont be faster than a same rpm HDD thats just a little larger. And the difference in time and power used to spin it up would be so small and insignificant they are basically equal.

 

Well...the 1.8" HDD will be more responsive to requests that the 2.5"HDD running at the same RPM as the disk platters have a smaller radius and so the disk head does not need to travel as far, making the smaller drive slightly quicker.

The downside is that storage capacity will significantly be reduced due to a smaller disk platter size.

As with 3.5" vs 2.5", I reckon the difference in performance will depend on WHICH two HDDs you are comparing. I'm guessing the performance difference will be very marginal, even in Benchmarking.

 

Yep, a smaller radius might give faster speed, both because the disk head doesn't have to travel as far, but also because disk density might be higher (more data packed into a smaller area, which means less movement is required to read the same amount of data)

It's not a big difference though.

 

It doesn't quite work this way, or rather, it's not quite as simple to compare as one might think. Generally, laptop hard drives fall behind their top-end equivalent desktop counterparts in performance by a significant amount. The smaller you go, the more performance you sacrifice as well - 1.8" drives are not going to be faster than 2.5" drives.

Yes, if given the same platter density and RPM, chances are the head won't have to go physically as far to find the next piece of data. This does not translate into faster speeds, though, because:

1. A 3.5" has a larger platter diameter. Given that data is written from the outside edge inwards, the rotational speed at the outer diameters is much greater in a 3.5" than a 2.5" given the same RPM. This means data gets transferred at a higher maximum rate, and it often is found faster as well.

2. 3.5" drives have less engineering restrictions on power consumption and performance targets because they don't need to satisfy notebook demands like increased resistance to shock and lower noise levels. They can use higher performance motors and chips.

Why 7200 Mobile HDDs - Hitachi GST
7200 RPM Desktop vs. Laptop HD specifications

1.8" vs. 2.5" specifications - including identical platter density

A good 2.5" hard drive may be able to beat a bad 3.5" hard drive given equal RPM; but that's about as far as you can get.

[Edit - grammar correction]

 

ok thanks.

 

Wow, the Interface transfer rate between the Deskstar and the Travelstar is pretty signifcant, 300 MB/sec vs. 1.5 Gb/sec. Just found that interesting.

 

Considering the best 7200RPM drive can't transfer more than 70MB/s as its theoretical peak, the interface doesn't make a scrap of difference.

(Also, 300MB/s = 2.4Gb/s)