Hard drive buying guide

We walk you through the process of buying a new hard drive, and explain all the jargon: from network-attached storage to solid-stated drives

It is worth mentioning that there are legal consequences surrounding the downloading of movies. It is illegal to copy commercial movies and music.

One constant source of confusion for buyers of hard disks is the disparity between the advertised size of the hard disk and the capacity that is reported by the operating system. More than one buyer has felt ripped-off when they installed their shiny new 500GB hard disk, for instance, only to find that the operating system tells them that the disk has a capacity of 465GB.

This is not actually an error: hard drive vendors and operating systems measure capacity differently. When calculating their disk size, vendors use a decimal definition of gigabyte. That is: one gigabyte equals 1000 megabytes, one megabyte equals 1000 kilobytes and so on. The operating system, however, will use the binary definition of a gigabyte when calculating available space. In binary terms, one gigabyte equals 2^10, or 1024 megabytes. One megabyte is 1024 kilobytes. So, using a decimal definition (as the hard drive vendors do) a hard disk with 500,000,000,000 bytes of storage is 500GB. But in binary terms, that's a little less than 465GB.


Another important specification to look for when choosing a hard disk is the interface. This is the kind of plug and cable system that it uses to connect with the other components of a PC.

For internal hard drives, the most common interface is Serial ATA 2.0 (SATA2). External hard disks will likely use a USB 2.0 or FireWire 400/800 interface, though eSATA — an external variant of SATA2 — is also available on some larger drives. You must choose a drive with an interface that your PC supports.

One important thing to realise is that the speed of an interface is not the same thing as the speed of a hard disk. For instance, USB 2.0 has a theoretical bandwidth of 480 megabits per second. Due to a variety of factors, including the speed of the components used, you will never actually reach these speeds in the real world. You will most likely have a peak transfer rate of around 40-50 megabytes per second over USB 2.0.


PATA, or Parallel ATA, is a legacy internal interface. It was once the ubiquitous connection for internal hard drives in IBM-compatible PCs. Sometimes referred to as IDE or EIDE, these connections are rarely used these days, although they are sometimes employed for connecting some optical drives. In contrast to the diminutive size of SATA2, Parallel ATA is a long, 40-pin connection with a flat ribbon cable which can be fiddly to connect.

If your computer was bought in the last few years, the internal drives will be attached using SATA or SATA2, though some older computers might require an IDE hard drive instead. Hard drive manufacturers no longer release their larger capacities models with a PATA interface, though if you look around, you should be able to find some retailers with PATA hard drives in capacities up to 500GB.


Serial ATA was designed to improve the transfer speeds of hard disks as well as eliminate some of the uglier aspects of PATA. It is the successor to PATA and has overtaken the older interface as connection of choice for hard drives in almost all circumstances.

When introduced, SATA — also known as SATA/150 — provided a potential throughput speed of 1.5 gigabits per second, making it faster than PATA connections while also being smaller and easier to connect. Since then, SATA2 has become the most common implementation of the interface, doubling the throughput speed to 3Gbps and providing a better method of handling multiple file transfers. SATA2 is backwards compatible with SATA/150, though drives that use a SATA/150 connection will transfer data at the slower speed.

SATA interfaces require a separate power connection for internal hard drives. IDE hard drives used a standard molex connection as a power source, SATA hard drives use a different connection that is easier to insert. This is only a potential problem for computers with older power supplies, as all newer ones come equipped with SATA power connections. If your computer is old then you will have to purchase a molex-to-SATA power adapter.

With the advent of solid-state drives, the bandwidth provided by SATA2 is nearing full saturation, necessitating a new specification to future-proof the interface. This comes in the form of SATA 6Gb/s. Since the specification is yet to be fully ratified, there are no hard drives that currently support this interface, but expect to see these drives by the end of the year.

Join the newsletter!

Error: Please check your email address.
Rocket to Success - Your 10 Tips for Smarter ERP System Selection

Tags solid-state drivesnetwork-attached storagestoragebuying guidehard drives

Keep up with the latest tech news, reviews and previews by subscribing to the Good Gear Guide newsletter.

PC World Staff

PC World
Show Comments

Cool Tech

SanDisk MicroSDXC™ for Nintendo® Switch™

Learn more >

Breitling Superocean Heritage Chronographe 44

Learn more >

Toys for Boys

Family Friendly

Panasonic 4K UHD Blu-Ray Player and Full HD Recorder with Netflix - UBT1GL-K

Learn more >

Stocking Stuffer

Razer DeathAdder Expert Ergonomic Gaming Mouse

Learn more >

Christmas Gift Guide

Click for more ›

Most Popular Reviews

Latest Articles


PCW Evaluation Team

Walid Mikhael

Brother QL-820NWB Professional Label Printer

It’s easy to set up, it’s compact and quiet when printing and to top if off, the print quality is excellent. This is hands down the best printer I’ve used for printing labels.

Ben Ramsden

Sharp PN-40TC1 Huddle Board

Brainstorming, innovation, problem solving, and negotiation have all become much more productive and valuable if people can easily collaborate in real time with minimal friction.

Sarah Ieroianni

Brother QL-820NWB Professional Label Printer

The print quality also does not disappoint, it’s clear, bold, doesn’t smudge and the text is perfectly sized.

Ratchada Dunn

Sharp PN-40TC1 Huddle Board

The Huddle Board’s built in program; Sharp Touch Viewing software allows us to easily manipulate and edit our documents (jpegs and PDFs) all at the same time on the dashboard.

George Khoury

Sharp PN-40TC1 Huddle Board

The biggest perks for me would be that it comes with easy to use and comprehensive programs that make the collaboration process a whole lot more intuitive and organic

David Coyle

Brother PocketJet PJ-773 A4 Portable Thermal Printer

I rate the printer as a 5 out of 5 stars as it has been able to fit seamlessly into my busy and mobile lifestyle.

Featured Content

Latest Jobs

Don’t have an account? Sign up here

Don't have an account? Sign up now

Forgot password?