The pros and cons of solid-state disks

The first hard disk, created by IBM in 1956, weighed over a tonne but could store only 5MB of files. Modern hard disks are smaller, cheaper and typically store 100,000 times more data.

The hard disk is an invaluable part of a PC because, unlike a computer’s main memory, which is wiped when the computer is turned off, the hard disk will retain files when there is no power running through the computer. They have also found their way into other devices including portable media players, camcorders and digital (Freeview) TV recorders.

However, the hard disk’s dominance over our computers is now being threatened by an entirely different storage device ­ the Solid-State Disk (SSD). SSDs are built with Flash memory, the same as is used in a digital camera’s memory card, which makes them much faster than hard disks.

The advantages
A hard disk is made of a set of platters on which data is stored, with a mechanical arm that moves to read sections of the disk. When you start up the PC or load an application, the computer has to wait until the hard disk’s arm moves to the section of the platter where the file is located, which slows down the PC.

An SSD has no moving parts so it reads data faster, which makes using a computer fitted with one faster and easier to use.

Because SSDs don’t have any moving parts, they require less power to work. For portable computers, this results in a much longer battery life. They are also more lightweight, more resilient and quieter in operation.

The disadvantages
Although a storage device promising super-fast loading times for programs and faster starting of the computer sounds like a dream come true, SSD technology has some problems.

The first is the price. A typical SSD is lot more expensive than an equivalent hard disk: currently the average solid-state disk costs in excess of £150 for a 64GB model. Considering a 1TB hard disk can now be bought for £60, SSD storage carries a much higher price per GB than a hard disk. This is why an SSD in a netbook may only offer 4GB or 8GB of space, compared with 160GB on the equivalent hard-disk-based computer. However, SSDs are becoming more affordable and capacities are growing.

Another problem is that SSDs slow down over time, as fragments of files left on the disk prevents it from making efficient use of free space. This problem is close to being solved as designers come up with ways to allow the SSD to remain efficient. The best of these, called Trim, is only supported in Linux, Windows 7 and certain SSDs but it should be more widely supported in future.

The third problem is that the Flash memory used in solid-state disks doesn’t last long enough. Each memory ‘cell’ in an SSD can only be written to a limited number of times. Although some Flash memory lasts longer, SSDs using that technology currently cost more than an entire PC.

To address the issue, all such disks use a technique called wear levelling to avoid writing to the same area more than they have to. It doesn’t completely fix the problem, but can improve the lifespan of the device.

Nevertheless, if you use an SSD it’s advisable to change the way Windows works on the computer to disable anything that makes constant use of the disk. Unlike a normal hard disk, you should never defragment an SSD as it will keep writing data to the cells, wearing them out, and does nothing to improve performance.

Windows also uses something called Virtual Memory, in which part of the hard disk is used for temporary storage. Users of SSDs have to be careful to move their Virtual Memory from the SSD to a hard disk. Some Windows features such as indexing will also write a lot of data to the SSD and are best disabled.

Our verdict
Solid-state disks can make a big difference to the overall performance of your computer. They’re now reliable and affordable enough to be worth consideration when buying a top-end computer. However, over the next few years they will become more affordable, so manufacturers will offer them in more ranges.

The technical issues we described are mostly solved, but older SSDs and most operating systems don’t currently support the new fixes. The longevity problem can’t be completely solved either, but wear levelling makes a difference. Hard disks have reliability problems of their own, and can also fail.

If you do opt for an SSD, it’s best to install Windows on it but make sure you also use a standard hard disk for file storage and virtual memory.

For most people the benefits of a SSD outweigh all its problems, apart from price. Once you use a computer with an SSD instead of a hard disk, it’s hard to convince yourself to go back to the old way.

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