Question: What does the 2.5″/3.5″ value indicate? The thickness?
I want one of my friends to buy 1TB hard disk for me. I know I want a 1TB capacity and 7200rpm, but don’t know how to choose between 2.5″ and 3.5″; I am worried that the 3.5″ drive may be physically too big.
Also, aside from the measurements, are there any other differences that may cause compatibility or usability concerns?
Answer: Another difference which is worth mentioning is that since 2.5″ drives are mostly used in mobile computers, main goal during design was low power consumption and other important factors were considered a lower priority.
Usually 2.5″ drives have lower capacity, lower cache and lower angular velocity compared to 3.5″ drives of similar price. For example at this time, largest consumer 3.5″ drives can store up to 3 TB of data, may have as much as 64 MiB cache memory and are ?7200 RPM or 10000 RPM. ?The downside is their power consumption which is generally around 5W. It is quite fine for desktop computers, but too much for battery operated devices.
On the other hand large 2.5″ drives are in the 1 TB range and usually have between 8 MiB and 16 MiB of cache. The number of revolutions in minute is usually 5400, but may be as much as 7200. Their power consumption is lower and for example WD10TPVT by Western Digital uses up to 2.5 W.
While these numbers change with each generation of hard drives, one thing that more or less stays constant is the difference between performance of the drives and the price difference. Usually high performance 2.5″ drive will cost as much as high performance 3.5″ drive but will have performance of mid-range 3.5″ drive.
Also 2.5″ drives may be more resistant to vibration than 3.5″ drives. For example some 2.5″ drives have accelerometers which can detect when drive is dropped and safely part drive head in order to minimize vibration damage. Such systems are rarer among 3.5″ drives, since desktop computers are usually designed not to be moved while working.