Choosing Step 5
Hard Disk Drive
Introduction
The Hard Disk Drive (HDD) is where all the data in a computer is stored when not in use by the processor. Unlike memory, data stored on a HDD remains intact when the computer is turned off. All the programs, documents, photos, videos, music etc that you keep on your computer are stored on the HDD and loaded into memory when you begin using them.
Choosing a Hard Drive is relatively simple and is usually based of 2 factors, size and speed. The size of the drive you choose will be primarily based on your personal needs, but for most people a drive not less than 160GB is a good starting point.
Speed is made up of a few factors, rotations per minute, cache and connection type. However for the vast majority of people a 7200rpm drive that connects via a SATA port will be the best option, leaving you simple to decide on the amount of cache you need (8MB, 16MB or 32MB). As explained below you will see very little difference in terms of performance once above 16MB.
If you are building a very high performance PC you may want to consider 10000rpm drives, though the price to performance level is relatively low. You may also consider RAID as a way of improving either performance or reliability of your storage. If you have the budget for it, RAID can also provide both reliability and performance improvements on the same storage. For more info on RAID, see our RAID choosing guide.
Examples
Budget PC
As always a Budget PC is about saving money, but instead of compromising on the quality of the drive, it's best to compromise size.
Home PC
A Home PC may require a reasonable amount of storage as usually multiple users will have music, videos and photos stored on it.
Gaming PC
A high performance (e.g. 10,000rpm) Hard drive can make a difference to the speed that games load, however they are extremely expensive and by no means essential, so we'll only use this drive for our highest example. The middle example will have its performance boosted by having 2 drives in a RAID 0 stripe.
Example Middle
Drive 1
Drive 2
Media Centre PC
Media Centre storage is all about size . The more films, music and recorded TV you can store the better. For our highest example well also use a RAID 1 mirror to help protect our media.
Workstation PC
For a workstation, very fast drives can be of great benefit, particularly for tasks such as online Video editing and transferring large blocks of files (e.g. a set of rendered frames). Capacity is also important, though this will depend on what type of work you will be doing.
Example 2D
Drive 1
Drive 2
Explanations
Form Factor (2.5" & 3.5")
Different sizes, or 'form factor' of hard drive
The form factor of a hard drive is its actual physical size. For computers these are split into two types, 3.5" desktop drives and 2.5" laptop drives. There are also 1.8" drives used in portable devices such as I-pods. Generally the maximum speed and capacity of these drives will go down the smaller the form factor. For building a desktop PC you will want a 3.5" drive.
Capacity (GB & TB)
Hard Drive capacity is measured in Giga Bytes (GB) and Tera Bytes (TB). 1 TB is equal to 1000GB. The capacity you need will be a personal choice based on how you intend to use your computer. For every 1GB of space you could either store 250 high resolution photos, 10 music albums or 1 movie.
You will want around 80-120GB free for programs and the operating system, so add this to the amount you think you will need for personal files.
RPM (5,400, 7,200 or 10,000)
RPM is the speed at which the 'disk' itself is spinning inside the drive. The faster it spins the faster the data can be written and retrieved. Most 3.5" desktop drives spin at 7200rpm with a couple reaching 10,000rpm. Smaller 2.5" drives usually spin at 4100rpm or 5400rpm, with a few examples of 7200rpm drives available. A good 7200rpm drive should be fast enough for almost any task, including playing the latest games.
Connections (SATA or IDE)
Most drives are still available with either SATA or IDE (also known as ATA or Parallel ATA) connections. Unless you have a particular reason to buy an IDE drive, we would always recommend SATA. The first version of SATA has a transfer rate of 150MB/s but now the newer SATAII can move data at 300MB/s. Although no drives can reach this speed yet, there are still significant performance benefits over IDE which can only transfer data at 133MB/s.
Seek Time (ms)
This is the time it takes the drive to find a piece of information and start reading it. It is usually measured in mille-seconds. For example a 7200rpm drive will have a seek time of around 8ms, which is more than adequate for most uses. Drives that have higher RPM speeds will have shorter seek times.
cache (MB)
The hard drive Cache is similar to that of an area of very fast memory where data that is read regularly is kept so that it can be retrieved more quickly. The more space the cache has the more data can be held for quick retrieval. In reality the difference in performance between an 8MB and 16MB cache sizes is minimal.
For more a more in-depth discussion of hard Drive choice and cache sizes check out this article on Toms Hardware.
Solid State Drives
There is a new type of Hard Drive making its way into the market, Solid State Drives. These use flash memory (similar to that in a USB pen drive) to give storage with lightening quick access times, silent operation and low power consumption. However they also have relatively slow transfer times when compared to traditional disks and are currently extremely expensive. As the technology improves we may well see them take the place of the traditional rotating Hard Disk Drive.
Related Links
Trusted Reviews: StorageGood source for non-technical reviews and news of storage drives, including a few benchmarks.
AnandTech: StorageGood source for technical reviews and news of all types of storage drives including Hard Disk Drives. Also has extensive benchmarks.
Wikipedia: Hard Disk DriveHard Disk Drive history and technical explanation of operation, design and implementation.
