Harddrive Guide:

Mega/Giga/Terabytes, Interfaces, Cache, RPM, RAID, Formats and More

Hard disk drives are physical devices to store electronic data- in case you were curious, yes, they actually use disc shaped platters, and the data is physically imprinted on these discs. There are a few terms worth understanding when purchasing a hard drive for your home or business.

Megabytes, Gigabytes, Terabytes - or MB, GB and TB

Any file of any type on your computer is stored on a drive, and takes up a certain amount of digital "space." Because all computer data is written in binary code (zeros and ones), each 0 or 1 takes up one bit- the smallest unit. Earlier computers could only handle 8 bits (zeros and ones) at a time, thus 8 bit segments became the standard, referred to as a byte.Continuing with multiples of 8 and using standard prefixes for thousand, million etc (kilo, mega, giga), we get the terms byte, kilobyte, gigabyte, and so on.

1 bit(b) = the smallest unit of data, holding a single 1 or 0
8 bits = 1 byte (B)
1024 bytes = 1 Kilobyte (KB)
1024 Kilobytes = 1 Megabyte (MB)
1024 Megabytes = 1 Gigabyte (GB)
1024 Gigabytes = 1 Terabyte (TB)

 

Based on average file sizes, a Terabyte harddrive can hold approximately:

200,000 photos
250,000 MP3s
25,000 CD Quality uncompressed audio files

Video:
76 Hours of Digital
380 Hours of DVD
120 Hours of HD

RPM Speed

The data on hard drives are actually written onto disc shaped "platters," and are viewed by "read and write heads" as they pass by. Therefore there is an actual physical process involved, and naturally a disc that can rotate more quickly can handle data more quickly. The standard rate for a high performance drive still tends to be 7,200 RPM (rotations per minute)- you will find most of the drives on this site use this speed.

Cache

Hard disk cache is much like the RAM memory in your computer, but is a bit more sophisticated and involved to integrate into the harddrives and thus tends to be more expensive.

Data recently accessed by your hard drive is stored in the cache, as it is often reused especially if you are working with one program. Your computer can access data in the cache much more quickly than having to physically scan the platters of the drive. Some programs and systems will anticipate data you may need for a program or task and put that information into the disk cache ahead of time for a smoother process. Disk drive cache is sometimes referred to as "soft cache."

Interfaces: or, how your drive connects to your computer

The interface involves a receiving port on your computer, a sending port on the external drive, and the proper cable connecting the two. There are multiple ways an external hard drive can connect to your PC or Mac.Fortunately, almost all more recent computers have USB 2.0 connection ports and almost all harddrives have USB 2.0 outputs, so there is little to no risk of a drive being un-usable on your computer (if your computer is from roughly 2001 or earlier though, check to make sure). There are however, different options for better performance that are more specific. Here is the complete list:

USB 2.0 - "Universal Serial Bus," the new standard in device connection- compatible with almost any computer, both PC and Mac. Max transfer speed: 480 Mb/s

FireWire 400 – High performance interface for Apple Mac computers. Max transfer speed: 400 Mb/s

FireWire 800 – High performance interface for Apple Mac computers. Max transfer speed: 800 Mb/s

eSATA (3 Gb/s) - Ultra-fast, eSATA speed allows external devices to have performance similar to that of top-of-the-line internal hard drives. Max transfer speed: 3Gb/sUnless it is a very recent purchase, your computer will most likely need an additional card to use eSATA connections.

RAID

Raid stands for Redundant Array of Independent Disks. This means that multiple drives are connected (often contained within the same unit,) and that data can be written, mirrored (identically copied) and divided among multiple drives. This not only improves performance, but also adds greater security from data-loss or drive failure.

Formats

Hard drives must be formatted before they can be read by a computer, but because this generally happens before a computer is sold, and many external hard drives come pre-formatted, there is a good chance that you have never had to deal with this. It is useful to know about however, even if you plan on purchasing a pre-formatted drive, especially if you are dealing with an unfamiliar brand or plan to buy a used drive / borrow from a friend, etc. There are a few standard types of formatting:

NTFS - The standard format for Windows 2000, Windows XP, Windows Server 2003, Windows Server 2008, Windows Vista, and Windows 7

HFS Plus - The Apple file system used on their computers as well as iPods

Brands

Here are the major companies in the harddrive market right now:

	Hitachi Following their corporate statement "inspire the next," Hitachi has been on the leading edge of several computer and digital innovations since 1959. They offer a wide range of reliable and affordable hard drives, both external and internal.
	Iomega Pioneers of the popular Zip drive, Iomega remains on the cutting edge of external / portable storage devices. They make a wide variety of hard disk products, from powerful desktop drives, to portable and rackmount solutions.
	Lacie LaCie is well known for their storage device products, particularly their external hard drives. Their external disk products have received awards from over a dozen major computer / technology magazines.
	Seagate Formerly Maxtor, Seagate drives are known for their high reliability and very low drive failure rate. They have been one of the most recognizable names in the hard drive business for a long time, offering quality external and internal drives.
	Western Digital Western Digital has been at the forefront of the hard disk / digital storage world for years. Their "notebook" portable drives are extremely popular, sleek and reliable, and their terabyte drives hold up to the same standards.