• How do hard drives work?
• What is a solid-state drive?
• Capacity
• Interface
• PATA
• SATA2
• USB 2.0
• FireWire
• eSATA
• Network-attached storage
• Form factors
• Internal or external?
• Hard drive specifications
• RPM
• Disk cache
• Native command queuing (NCQ)
• Seek/access time
• MTBF
• Warranty
• Noise
• Buying the right hard drive
• File systems, fragmentation and slow downs
• RAID

<---> USB 2.0

USB 2.0 is a common interface for plugging in peripherals like mice and printers. It can also be used to plug in hard disks. The USB interface is exclusively an external connection, so you can't buy an internal hard drive with a USB port.

USB 2.0 has a theoretical transfer rate of up to 480 megabits per second (60 megabytes per second), which is generally sufficient for data transfers.

The biggest benefit of USB 2.0 is that it is plug and play. Users who run Windows XP or later versions of the operating system on PCs, or Mac OS X on Macs, can plug most USB 2.0 devices straight into a computer and not worry about installing extra software to use them. Provided an external hard drive has been formatted with a compatible file system, users can start using it within a few seconds of connecting it.

USB 2.0 does have one drawback: the interface provides enough power for smaller, notebook-sized external hard drives, but larger drives may need access to mains power via a separate adapter. Some USB external hard drives will use two USB ports, with the second one usually used for additional power.

Because USB 2.0 is backwards compatible, it is possible to plug USB hard drives into older PCs that only support USB 1.1. USB 1.1 is very slow, however (only 12 megabits per second) and will make accessing data on the hard disk extremely slow.

<---> FireWire

Much like USB 2.0, FireWire (also known as IEEE1394) provides an external high-speed port into which you can plug hard disks. FireWire comes in multiple forms with different connections, and the most popular are FireWire 400 and 800. Despite offering speed benefits over USB 2.0, FireWire has never become a popular standard on PCs. Some PCs come with a 4-pin or 6-pin FireWire 400 port, but FireWire 400 and FireWire 800 connections are more common on Apple Macs.

The different versions of FireWire are named after their theoretical bandwidth — FireWire 400 operates at 400 megabits per second, while FireWire 800 doubles the speed to 800Mbps. There is also a FireWire 1600 and forthcoming FireWire 3200 standard (which competes with USB 3.0 and eSATA) but these are virtually unused by consumer PCs and hard drives.

Though the FireWire 400 is slower than USB 2.0, which operates at 480Mbps, tests have shown that FireWire is actually a more efficient carrier of high-volume data and is often preferable to USB as a hard disk interface.

Much like USB, FireWire also carries a limited amount of power (enough for small external drives). Both FireWire 400 and 800 standards have the added benefit of efficient daisy-chaining. This allows users to connect extra FireWire devices to each other, rather than directly to the computer, so the devices can communicate with the computer while only taking up one FireWire port.

<---> eSATA

External SATA, or eSATA, is by far the fastest external interface available on consumer hard drives, providing the same 3 gigabits per second bandwidth as an internal SATA2 connection.

Despite the speed of eSATA, there are still some drawbacks to the interface. The maximum length of the cable used is one metre. eSATA doesn't transmit power over the interface either, so you will need access to a power outlet. The connection still offers plug-n-play capability, so drives will become instantly accessible when plugged in.

eSATA interfaces are usually only available on higher capacity external hard drives. These drives normally come with USB 2.0 and FireWire interfaces as well.

While eSATA connections are slowly becoming more common, there are still many hard drives and computers that do not offer the connections. If you plan on purchasing an eSATA-equipped hard drive but do not have the sufficient connections on your computer, you can easily upgrade a desktop PC through a PCI/PCI-Express Card for around $40, or a notebook through ExpressCard or PCMCIA for the same price.

<---> Network-attached storage

Networked-attached storage devices (NAS devices) are essentially external hard drives with network ports and some server capabilities. Computers on a local network can access the data on a NAS device's drive (or drives).

While traditionally used in business environments, NAS devices designed for use in the home are becoming more common. They can be used to stream videos, audio and pictures directly to a television (if the TV has built-in media streaming support) or via a media streamer or similar device. They can also be used to back up computers' hard drives. Some NAS devices offer server capabilities such as Universal Plug-n-Play (UPnP), an iTunes server, and even a Web or FTP server for remote access.

NAS devices sometimes support hot-swapping of drives (removing and replacing individual hard drives without turning the device off) and may have multiple drive bays. A NAS devices with a single drive bay will currently let you store up to 2TB of data, but some devices can accept up to eight or 10 hard drives at a time. These offer various RAID configurations for better performance and backup redundancy. RAID allows you to group together two or more drives so that the operating system treats them as just one single drive. There are different types of RAID that can be used, depending on whether you want more speed from your computer or better data reliability.