Disc Slow Down for XP Users

Tactics used to make new hard drives more efficient could cause problems for Windows XP users. It may mean any new drive bought after next year could be noticeably slower to use on the operating system.
The issue involves the way hard drives are broken down into individual sectors. Until now, it has always been standard for hard drive sectors to be 512 bytes in size. However, not all of each sector is used for storing data. Instead, there is a marker to denote the start of the sector: a space used for codes which are used to check if there is any error with the sector and its contents, and a space between each sector. (Source: arstechnica.com)
The larger the drive, the more sectors there are, and thus the more space unavailable for data storage. While this wasn't a problem in the past, with today's larger drives it has become a significant issue.

512 Byte Sector Limit Scrapped Next Year
The International Disk Drive Equipment and Materials Association (IDEMA), the global body for drive manufacturers, has now agreed that all drives produced after January next year will use sectors which are 4 kilobytes, which is 8 times larger in size than the standard 512 bytes.
The 4 kilobyte sectors have two beneficial effects: first, it cuts down the amount of disk space used simply for spaces between sectors by seven-eighths (87.5%). Second, it allows more space in each sector to be used for error correction codes. This should drastically increase the reliability of drives.

XP Users Could See 10% Dip in Performance
The problem comes from the fact that while Vista and Windows 7 were both designed with 4K sectors in mind, XP was created long before the industry had decided it would eventually be a standard successor to 512 bytes.
XP can work with a 4K sector based drive, but will simply treat it as if it used 512 byte sectors. This will be fine for reading information, but will introduce an adjustment step when writing to make sure the data fits the sectors correctly. Though this will only take an additional 5 milliseconds, that works out as a decrease in speed of up to 10%, which is likely to be a noticeable deterioration, especially with many files stored on the drive.

Later Systems Unaffected
In addition to Vista and Windows 7, all versions of Apple's OS X system from Tiger (released in 2005) onwards will work fine with the new drives. Most modern Linux based systems should be OK and, being open source, it's much easier to upgrade those which aren't. (Source: bbc.co.uk)
For XP users, it may be a judgment call as to whether the problem is disruptive enough to justify updating to a later operating system at the same time as getting a new drive.