The problem these days with computers isn’t the MIPS: it’s something not so obvious –‘latency’. Roughly speaking, latency is the gap between the CPU wanting to do something and being able to do it. A lot of effort has gone into microprocessor ‘pipeline’ architectures – queuing instructions for efficient execution - and first and second level on-chip instruction caches where instructions are held ready for the microprocessor to run. In addition, memory access speeds have improved with DDR RAM and similar technologies. But the one place where latency hasn’t improved is with the good old hard disk. While the CPU can execute an instruction in a fraction of a nanosecond, it still takes milliseconds to get the data to the microprocessor in the first place. To put it another way, the microprocessor can execute instructions ten million times faster than it can get them!

Most people, most of the time, only think about the disk when it either gets full or makes a horrible scrunching sound as it dies. Disks are neglected. But paying a modest amount of attention to your rotating metal can – and often does – improve performance dramatically. Windows seems to allocate files by trying to use the disk as ‘efficiently’ as possible. In Windows terms, this means that the file can be (and usually is) spread over the disk in several parts. When a program comes to read the file, the disk has to move physically to retrieve the various parts of the file. This takes, in CPU terms, forever.

It’s a good idea then, to try and keep each file in one piece so that the read or write can take place in one go. This is where defragmenting your disk comes in. And the tool to use is Diskeeper. In fact, Diskeeper comes bundled in with Windows XP. If you look under ‘Programs, Accessories, System Tools’ you’ll see a Disk Defragmenter. This is an entry level version of the full Diskeeper package.

There are several differences between the full Diskeeper and what you get for free. To me, the main one is the ability to perform a ‘boot time’ defragmentation which allows you to defragment and modify the Windows Master File Table or MFT which is used to store much of the file system’s data. The full version also has the ability to continuously defragment your disk with Diskeeper’s ‘Set It and Forget It’ option which runs in the background, keeping your disk at optimum capability. Additionally, the full version also runs up to five time faster than the free version (see the details here).

So how does it work in practice? I found that, with a slightly defragmented disk, running Diskeeper didn’t make that much obvious difference to its performance. Even though my most commonly used files were very fragmented, Windows caches the files by using a fair chunk of the available main memory; as a result, the commonly used files are already entirely in memory. But on a heavily fragmented disk – for example on my laptop which has a slowish 5400 rpm disk, as laptops typically do - it made a huge difference. Loading a big Visual Studio project was noticeably faster – about 30 seconds faster – after running Diskeeper and defragmenting the disk.

On my desktop PC, where I hadn’t done a defragmentation in living memory, the speedup was also very noticeable. Program opening – again Visual Studio - was a good bit snappier having done a defragmentation run.  This illustrates the advantages of using the ‘Set It and Forget It’ option, by the way. People, myself included, just don’t remember to defragment their disks. One other effect: shutting down my PC took a lot less time too.

Diskeeper 10 has a number of improvements over the previous release. The user interface is somewhat clearer; not that it really needs to be - defragmentation is, after all, just a matter of setting Diskeeper going. Executive Software says that Diskeeper 10 has been internally redesigned. In particular, the Intelligent File Access Acceleration Sequencing Technology (I-FAAST) monitors your disk to determine which files are accessed most often and positions them so that they can be accessed faster. Also of interest is the way Diskeeper intelligently monitors the windows I/O queue so that the background defragmentation operations are suspended when you want to do something – compile a program, say. This seems to work quite well. With the previous version of Diskeeper, the background defragmentation did produce a noticeable performance hit when it was running. I can’t say that I notice Diskeeper 10 at all. But then, if Diskeeper is working correctly, that’s as it should be. This is totally unlike my virus scanner, incidentally, which kicks into life at a certain time every day on my PC and reduces performance to the that of the proverbial slug on tranquilizers. Virus scanners please take note!

Interestingly, defragmentation doesn’t seem to be much of a problem with Unix systems. I suspect that this may be down to the historical (and intentional) way that Windows allocates file storage. Most Windows systems sell, and have sold, into the consumer market where today the difference between a 100GB disk and a 160GB disk may only be a few dollars. But in the past, the price difference between a 1GB disk and a 4GB disk was substantial. Whatever the cause, the current mechanism for file allocation in Windows is distinctly sub-optimal and if you want tip-top performance, you must defragment. For home users, suffering a small performance hit due to defragmentation isn’t going to matter much. But for a professional software developer, I think Diskeeper is well worth it. Put it this way: woodworkers don’t use blunt tools and programmers shouldn’t have to put up with slow disks.

Dermot Hogan

January 2006