Pushing the limits of computer hard drives is silly when all we need is a lot more memory.

Most of us want as big a hard disk as possible – not only do we have to keep all our giant Photoshop images and video archives there, now an iTunes library is likely to take up a further 20GB or so. But hard drives aren’t just about capacity. Depending on the amount of cache and RAM installed in your workstation, they’re also a brake on your speed.

When you’re working on a file, you should keep as much of the data as possible in memory. When not all the file’s data is humming along in RAM, your computer has to fetch this stuff to and from your hard drive. In terms of performance, this is like locating your desk a mile from your filing cabinet.

Even today’s disks are a thousand times slower than the fast parts of the computer. Hard disks typically work a few thousand times slower than RAM, which in turn is many times slower than the processor driving the system. Comparing the speed with which a processor talks to RAM and video memory to the speed at which a disk operates is like the speed difference between a speeding bullet and a slow human walk.

The processor is so fast that it ends up spending much of its time waiting for the slower parts of the computer to catch up. This speed difference is key because the human perception of computer response (whether we judge an application to be fast and responsive or slow and unusable) is largely driven by what happens at processor, RAM and video subsystem speeds – not the hard-drive’s. A fast, elegant user interface tosses billions of bytes back and forth between processor and RAM to make the user experience smart and easy. The disk itself is so slow that even making it 100 times faster wouldn’t register at end-user level when comparing UI performance.

But in battling with heavy-duty images, video and sound, hard-drive speed can make all the difference when you don’t have enough RAM to store all the required data. Recently, scientists have found that the theoretical maximum speed that data can be written to a PC’s hard drive is 435,000 million bits per second. That’s an impressive thousand times faster than the best magnetic hard drives in use today. But by the time this limit is reached the faster parts will be even speedier, keeping the disk as the perpetual poor relation in the PC mix.

If you thought that your broadband connection is lightning fast, you’re deluding yourself. The difference between glacial disk speed and Internet rates is equivalent to a jogging human and the slowest crawl of a snail. Even a fast Internet connection is a thousand times slower than a local hard disk, and approximately a million times slower than chip/RAM accesses.

Of course, today’s technological limits are tomorrow’s geek jokes – much like Bill Gates’ 1981 assertion that PCs would never need more than 640K of RAM. At the dawn of the railway age, people believed that you’d die when travelling at more than 21 miles an hour. Who knows what technological advances will propel us forward in the future. If we can get near-instant downloads from the Web, our workstations could work many times faster than we can think – which puts us into dangerous Terminator territory. Maybe we should be happy with what we’ve got now, or just buy some more RAM.