Why 2.5 hard drive is usually sold at a higher price, does it mean that it's usually more durable than 3.5?
And why for most desktop PC, they use 3.5 internal drive, I don't see any 2.5 internet drives sold in the nearby computer market. and why?
2.5 drives are more expensive primarily due to greater manufacturing difficulty. There are differing opinions regarding reliability but likely the differences are minor. 2.5 consumer grade drives are designed primarily for laptops where a major priority is low power consumption. Everything else is a nice to have but not if it seriously compromises power consumption. 3.5 drives are available in larger capacities. For desktop use 2.5 drives have few advantages over 3.5 drives.
Generally 3.5" drives have a higher spin speed giving faster access than 2.5" drives but there are exceptions
I guess higher spin rate = more heat produced -> more wear but I could be wrong. Of course this isn't applicable to Solid State Drives.
The cost difference is primarily caused by the media. Media of all types and sizes are never perfect ie they all have defects/bad tracks and some more that others. Since the 2.5" is quite smaller physically vs the 3.5" drives, the media needs to be more perfect for 2.5" drives vs 3.5". The yield of platters/media for larger capacity are fewer and thus will cost more.
The same reason applies to 7200rpm vs slower drives. They cost more because they have to fly the heads closer to the media which requires a Platter surface to be smoother and less defects. Since all platters are not created equal there are fewer of them which raises the price. However platters that can't be used for 7200 drives could be used in slower drives.
This also applies to platters/media of lower capacity which are the same as those used in higher capacity drives, but contain more defects. They are fine for the capacity of 250gb vs a 750gb.
Bottom line is that lower capacity and slower speed drives cost much less then the higher speed/capacity drives.
Does WD or Seagate usually make a portable drive of better quality??
I have had good luck with Toshiba portable drives (Canvio).
Desktop PCs use 3.5" drives as there is room in the box, power available, capacities are greater, and performance is better.
You can put 2.5" drives in a desktop if you like, but there is no point in doing so. They are primarily for Notebooks and designed for lower power consumption and small size.
The durability is the difference between Consumer drives and Enterprise drives which are more expensive and have longer warranties and should last longer.
" more wear but I could be wrong. Of course this isn't applicable to Solid State Drives."
Oh really, and what about at an atomic/molecular level with an SSD, there is wear on solid state memory cells. That is the point of TRIM and the controllers on SSDs to even out the wear on these solid state memory cells.
Heat is also a factor in SSDs, as in all solid state devices.
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