External Hard Drives - Buyers Guide

External Hard Drives are becoming more and more popular as they connect externally and do not require any installation. They present a convenient media as back-up drives or a second hard drive. External Hard Drives come in many different designs and are available for most of the laptop ports that can serve for data transfer such as USB, FireWire and PCMCIA. Also, by using adapters, you can now plug in SCSI, Serial ATA and IDE type external hard drives that prior were only available for PC's as internal drives.

External hard drives - these are important characteristics to consider:

• Speed (or transfer rate) - in MB/sec - depends on connection type
• Capacity - in MB
• Portability
• Price

The first two characteristics directly depend on what your external hard drive will be used for, and, to get the best performance, I suggest that you use this table as a guide:

All three characteristics combined will define the price. There is no need to spend more money on a more expensive external hard drive designed for gaming if all you are going to be using it for is backup. Also, portable drives are more expensive and while are smaller and weight less they may not worth the money.

Speed (or Transfer Rate)

As mentioned above, Speed or Transfer Rate depends on the interface type or connection type that an external hard drive is designed for. Your laptop would have to have the same interface to be able to connect the hard drive (e.g. a USB port to connect a USB drive, a FireWire port to connect a FireWire drive).

Here's how speed or transfer rate depends on the interface or connection type used in the external hard drives:

Often, transfer rates are provided in MBits per second that is very inconvenient when comparing with the capacity' MBytes. Here's Conversion from MBytes/sec to Mbits/sec:

1 MByte/sec = 8 Mbits/sec

...But let's make sure everyone understands... the transfer rates provided by the external hard drives manufacturers are not the actual rates you are going to get but it is what is supported by the drive. What you'll actually get is only 60-70% of supported rates depending on type of connection.

If your laptop is not equipped with an appropriate interface (or port) then you can always get an adapter - see these pages for particular external hard drives types and their related adapters: USB hard drives, FireWire hard drives, PCMCIA hard drives, SATA hard drives.

* Drive Capacity Calculator

Use these examples to figure out the capacity you need. Each 20GB holds up to:

• 20 hours of MPEG digital video
• or 5,000 four-minute MP3's
• or 2,000 high-resolution digital photos
• or 50 video games

Hard Drives Portability

Portability - this is one more feature to consider when buying your external hard drive. Depending on your life style or mobility requirements you may want to choose a portable drive - it'll be more expensive.

External Connection Type (or Interface Type)

Again, as you saw in the table above, external hard drives differ by interface type or connection type. Drive's speed and price depend on it. This table gives brief overview of external hard drives available on the market by interface type:

USB Hard Drives	Most Common, Average Speed, Low Price, Connect to USB1.1 & 2.0 ports
FireWire Hard Drives	Second Most Common, Average Speed, Low Price, Connect to FireWire 400 & 800 ports (same as iLink or IEEE-1394 ports)
PCMCIA Hard Drives	Highest Portability, Low Speed, Low Capacity, High Price, Fit into PCMCIA slot (also called PC Card, NIC Card, Ethernet 10/100 or CardBus slots)
SATA Hard Drives	Highest Speed, High Price, Connect through an adapter plugged in into USB, FireWire ports or PCMCIA slot
SCSI Hard Drives	Second Highest Speed, High Price, Connect through an adapter plugged in into USB, FireWire ports or PCMCIA slot
IDE Hard Drives	Third Highest Speed, High Price, Connect through an adapter plugged in into USB, FireWire ports or PCMCIA slot

To help you to choose between the external hard drives and internal hard drives see my laptop hard drives guide.

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