hmm....i'm a noobie in external hard disk.....so can i know what should i take note when i'm buying an external hard disk besides the transfer speed,capacity,cache??? The bigger the cache the faster the transfer speed right?? Then is Seagate the best brand for external hard disk?? Then do external hard disk have that SATA 1 or Raid0 thingy???

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Added on September 26, 2009, 6:41 pmoh...can anyone make a brief explanation on SATA or Raid thingy??? it's very confuse when reading the wikipedia explanation....do i need to take note about the SATA/Raid thingy when buying external hard disk?? If yes, how? Thanks a lot for enlighten me.

When it comes to external hard disks, there's only three main connectors: USB 2.0, e-SATA and FireWire (a bit rare).

USB 2.0 has a data transfer bottleneck of about 30 MB/s - performance will be poor no matter how much money you throw at it. e-SATA has a bottleneck of about 150 MB/s. I forgot FireWire's bandwidth, but it is higher than USB 2.0. FireWire and e-SATA externals are superior here.

Edit: You'll need to have either a FireWire port or an e-SATA port to support either FireWire or e-SATA devices. Most current motherboards or laptops support these, but not older ones. It is possible to buy expansion cards to add support for older desktop motherboards, but they'll cost you extra.

Other considerations are power supply. 2.5" USB external hard disks can run entirely off that USB cable, any FireWire device could potentially run off that FireWire cable, but anything else requires a separate power cable.

RAID is not related to SATA. SATA is a connector and RAID is treating multiple hard disks as one.

RAID doesn't really apply to simple externals. The best place to get them is with a NAS or a SAN (they're actually the same thing - some network attached storage). As RAID requires more than one hard disk, they're not cheap.

There are:

• SATA 1.5 Gbit/s aka SATA1 (max 150 MB/s)
  
• SATA 3 Gbit/s aka SATA2 (max 300 MB/s)
  
• SATA 6 Gbit/s (max 600 MB/s)
  
• e-SATA (same as SATA 1.5 Gbit/s or max 150 MB/s)
  

Source: http://en.wikipedia.org/wiki/Serial_ATA

Only e-SATA is usable with external hard disks.

However, it may be possible to remove the hard disk from the external casing and put it in your desktop or laptop (depending on size).

On another note, most hard disks have a sustained read/write that is much slower than 150 MB/s. The 7200 RPM WD 1 TB Caviar Black for instance maxes out at ~110 MB/s, quite a distance from the 150 MB/s theoretical limit of e-SATA.

Only the SSDs need SATA 3 Gbit/s to perform well and they're best used as internal drives because they're wasted as externals.