3. Physical format
The first thing to decide is the physical format of the hard disk. There is 2 main formats of hard disks, namely :
- 3″1/2 : This is the format of hard disks for desktop computer.
- 2″1/2 : This is the hard disks for laptop.
So the choice is simple, if you need a hard disk for your laptop, you need a 2″1/2 hard disk otherwise one 3″1/2.
There is still the problem of external hard disk. In this case, the hard disk is directly inside a container, so this is not a big problem. If you search a little hard disk, opt for a 2″1/2 else in most cases, choose a 3″1/2.
The next thing to verify in the interface of the hard disk. That is the way the hard disk will be connected to the motherboard. You cannot connect a SATA hard disk on a motherbord that have only IDE. Here are the main existing formats :
- IDE (PATA) : This is the oldest interface, but also the most used one. The transfer rate is lowe than the other, but is even so acceptable for a normal usage. In its ATA133 version, the theorical transfer rate is 133 Mo/s
- SATA : This interface has better transfer rates than PATA. There is two versions (SATA I and II). They have transfer rates of, respectively 150 Mo/s and 300 Mo/s.
- SCSI : This interface is still better than SATA, but really the expansive and especially made for servers. Its theoretical transfert can go to 640 Mo/s.
- SAS : Serial Attached SCSI : This is the evolution of SCSI. The transfer rate is better and not distributed between hard disks. But this format is not really widespread and exclusively reserved for servers at this time.
You also have to keep in mind that hard disk are limited in tranfer rate due to their mechanic state. So the transfer rate of the interface is mostly useful when several hard disks are connected on the same bus.
For a new PC, it’s recommended to opt for SATA hard disks who are the new standard for hard disk. If you really want big transfer rates with many disks or if you want to build a server, you can choose SCSI or SAS depending on your budget.