George Ratzlaff plans to buy an SSD to speed up his PC. How big a drive does he need?
Before you buy an SSD, decide if it's going to replace your current hard drive, or if you'll keep both the old and new drives, letting the SSD supplement the spinning platters. If you're supplementing, you can get away with a smaller SSD and therefore save money. (As I write this, $60 can buy you a 120GB SSD or a 2TB hard drive.)
But supplementing the drive may not be practical. If you have a spare drive bay in your PC--common in desktops but rare in laptops--you can easily supplement. But if your PC has space for only one hard drive, replacing the drive will likely make more sense.
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If you're supplementing, you need only an SSD large enough to contain Windows, your installed programs, and maybe a handful of commonly-used documents. Everything else should remain on the spinning hard drive.
Yes, the hard drive will slow down the PC when compared to one with only an SSD, but not by much. Since all of the files you're regularly using are on the SSD, the performance hit will often be non-existent and rarely noticeable.
My test computer (a homemade desktop with a lot of bays) has a 120GB SSD. It has Windows 7 Ultimate installed, along with a huge number of programs (I use this computer to test software), and 14.2GB of documents, songs, and photos in the libraries. And that doesn't quite fill up two thirds of the drive.
If you don't have a spare bay, replacing your hard drive with an SSD makes a lot more sense--even though that means buying a larger, and therefore more expensive drive.
How large are we talking?
The obvious answer: At least as large as your current hard drive. But if that's too expensive, take a good hard look at your current drive. Is it half empty? If so, consider a smaller drive, although pick one that's still large enough for reasonable growth.
If that's too expensive, you can still use a smaller, supplemental SSD. After you remove your hard drive, put it in a USB enclosure, which effectively turns it into an external hard drive. And keep that external drive plugged into your PC, so you can access files that didn't fit on the SSD.
But there are two problems with this approach: First, the external drive will make the laptop a little less portable. And second, access to files on the external drive will be considerably slower, especially if your laptop lacks a USB 3.0 port.
Once you've purchased your SSD, be sure to read my instructions for transferring your files.