There are several ways to improve an older laptop's performance, including upgrading the processor or adding more memory, but replacing the stock hard drive will often provide the best performance gains for the least amount of money. Depending on your budget, there are several replacement options that can increase the speed of your laptop.

Larger Drive

Simply upgrading to a larger hard drive can increase the performance of a computer, especially if the hard drive is nearly full of data. A hard drive writes data to its platters from the outside to the center. Because the hard drive spins at a constant rate, accessing data on the outside tracks is much faster than accessing data that is stored toward the center. If you upgrade to a larger hard drive, more of your data will be towards the outside tracks, resulting in slightly better performance for relatively little cost.

Faster Hard Drive

How quickly a hard drive can access its data is relative to its spindle speed, measured in RPMs. Typically laptops come equipped with 5400 RPM drive, but but by upgrading to a 7200 RPM version, you will have much better performance overall -- it'll be especially noticeable when the computer boots and when large programs are launched. A 7200 RPM hard drive is slightly more expensive than a 5400 RPM model of a similar size, however. Due to the faster spindle speed, 7200 RPM models also tend to be louder and they use more power than slower drives, possibly decreasing the battery life of the laptop.

Solid State Drive

Solid state drives, or SSDs, are one of the best ways to increase the performance of an older laptop. Instead of using spinning magnetic disks to store data, SSDs use non-volatile flash memory, which is similar to the memory cards used in cameras and phones but much faster and more reliable. Unlike a hard drive that has to wait for its read heads to physically find the data on the drive, SSDs can find the data near-instantly. The newest models are much faster than a traditional hard drive, they use much less power, make no noise and they can withstand physical shocks or bumps that could cause a hard drive to fail. Compared to hard drives, however, SSDs are much more expensive for a similar amount of storage space.

Physical Size and Interface

Before you replace the hard drive, you will need to know the physical size of the old one and its interface type. This information can be found in the computer's documentation or on the old drive itself. Laptop hard drives are typically 2.5 inches wide, but there are several common thicknesses, including 5, 7, 9.5 and 12 MM. A thinner hard drive may work in a bay designed for a thicker drive, but typically the new hard drive should be the same thickness as the old one. The interface is typically either SATA or PATA, running at a set speed. The drive should meet or exceed the speed of the laptop's interface, though the safest option is to use the same speed to ensure compatibility with your laptop.