The Hidden Bottleneck of Computers

This actually isn’t hidden at all, but I spent a while earlier on Amazon looking at various non-fiction books, and they all have dramatic titles like that.

You’re going to buy a computer, and you want something good. These are the factors I think most people look at:

  • Processor: number of cores, speed (in GHz) of processor
  • RAM: amount thereof (in GB these days)
  • Hard drive: capacity (in GB) of the disk
  • Screen size (primarily for laptops)

For what I do, processor speed is rarely a bottleneck. Obviously this isn’t true for anyone, but if you’re a normal computer user who does word processing, spreadsheets, e-mail, and web browsing, any new PC is going to have a good enough processor for you.

As far as RAM, although there are lots of technical specs like bus speed and CAS latencies, consider RAM a commodity. (Except that RAM from one computer might not work in another.) Short of literally-broken RAM, there’s no such thing as “good RAM” and “bad RAM.” You just want a lot of it. I wouldn’t buy a computer with less than 2 GB. You can get by with 1GB. I find 2GB to be plenty. I see 3GB a lot. 4GB is the maximum most ‘normal’ (32-bit, Windows) machines can take, and there are apparently some issues that keep Windows from seeing more than 3.5 or so. So aim for 2-4 GB.

Screens: my advice would be to just try it. Screen size only tells you the physical size; what really matters is the resolution. But you also have to wonder about brightness, contrast ratios, refresh rates… The easiest thing to do is play with the computer in the store and see what you think.

Hard drives, though, are what led me to create this post. Most people seem to just look at the capacity: a 100 GB hard drive is better than a 40GB hard drive. Indeed, it holds more, and you need to make sure you get a capacity that’ll work for you. But what I’m increasingly noticing is that no one pays attention to what I think is a more important metric: how fast the hard drive is. In my experience, my hard drive is almost always the bottleneck. Computer takes a while to boot? That’s because it’s reading everything off of the hard drive. Programs slow to load? Waiting on the hard disk! There are a lot of scary metrics you can look at with hard drives, but I’m going to suggest that there’s really only one that matters for most consumer machines: RPM. Depending on who you ask, it’s either Revolutions or Rotations Per Minute, and it’s basically “how fast the disk spins.” Much like a CD (or a vinyl record, which people might be more familiar with actually seeing move), your hard drive consists of several “platters” with information stored in circles around them. (Very oversimplified.) To read or write data, the disk is spun around, and the “head” will read the data. Thus it stands to reason that you want that disk spinning as fast as it can.

For a laptop, the range is generally 4200 to 7200 RPM, though I’ve heard of 3600 RPM drives in the past. Pay a little more if you have to, but get a 7200 RPM disk. You’ll be alright with a 5400 RPM disk, too. But don’t take a 4200 RPM disk, even if it’s a great deal. You’re going to feel the effects every single time you use your computer. A higher RPM means data will be accessed more quickly, which means your files will save faster, programs will launch more quickly, and your computer will take less time to boot. Higher-capacity hard drives often run at the lower end of the spectrum, though it needn’t be that way. But is a 200GB laptop hard drive really any good if the computer’s always going to be miserably slow?

So 7200 RPM is what you want for a laptop, but 5400 RPM might be acceptable. If you’re buying a desktop, though, you can do better. 10K RPM drives exist, though they’re currently very expensive and rare. (10K RPM, and even 15K RPM drives are commonplace with high-end servers, but tend to be extremely expensive and use SCSI/SAS connectors that your home machine almost certainly doesn’t have.) But 7200 RPM drives are very common on desktops, moreso than on laptops. So if you’re buying a desktop, a 5400 RPM should be considered bottom-barrel.

I’m not saying that the speed of the hard drive should be the only thing you look at. Of course you want a laptop with a nice screen, and you want good software pre-installed, and all that. And I really can’t stress how awesome having a lot of RAM is. But if you’re in the market for a new machine, you owe it to yourself to investigate disk speed, because it will make a noticeable difference in your everyday computer usage.

4 thoughts on “The Hidden Bottleneck of Computers

  1. Speaking of, I inherited two Raptors from a former coworker that are just waiting to be installed in my workstation… what a wonderful Friday project.

  2. *drool*

    I’ve always thought that the “model” desktop system would have something like a 500GB SATA disk (or a RAID5 array) for general data, but something like a striped pair of 18GB, 15K RPM SCSI disks for swap/paging, scratch files, and the like. Stuff where performance really matters.

    But then! One day I realized that I used to think that it’d be a horrible idea to put, say, your boot loader, or the core OS, on a striped set — if one disk fails, you lose the whole thing. Which stinks because having the “core OS” and the like is exactly what you want on fast disks, for super-fast loading, booting, etc.

    But what I realized is that the OS/boot loader/etc. is exactly what you want on your fast, “risky” stripe set — even though the system won’t boot, you just plop in a LiveCD and rebuild. Your data is safely on a non-risky set.

    Of course, my fantasy of a system stuffed full of finely-tuned hard drives is somewhat hampered by the fact that I have a laptop. *g*

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