Solid State Drives

Replacing a hard drive with a solid state drive is like getting an instant upgrade - a much newer and faster computer. You'll be amazed at the performance boost you can get for a small fraction of what you would have spent on a new computer. Under no circumstances buy a laptop with Windows running on a hard drive unless you have the technical skills to replace the hard drive with an SSD.

Solid state drives have several form factors. SATA is the standard hardware interface for connecting hard drives, SSDs, and optical drives.

2.5-inch SATA SSD

These SSDs have the same form factor as a 2.5-inch hard drive in a laptop and can be used to upgrade system drives.

Put the 2.5-inch SSD into a USB enclosure temporarily. You can get an Orico enclosure for about $12.00 on Amazon.
Use a backup utility to clone the hard drive onto the SSD.
Remove the hard drive and replace it with the SSD.
Put the hard drive into the USB enclosure and use it for secondary storage.

mSATA SSD

The mSATA designation refers to mini-SATA. It's a compact format, only one-eighth the size of a 2.5-inch SSD. It uses the PCI Express Mini form factor and connector.

Beware of laptops that have a hard drive and a 32GB mSATA SSD used only for file caching. This "Intel Smart Response" architecture is obsolete technology that existed when SSDs were new and more expensive than they are now. If you have one of these, there are two options:

Replace the 32GB mSATA SSD with a newer and larger one that functions as the system drive. Use the hard drive for secondary storage or replace it with a 2.5-inch SATA SSD.
Replace the hard drive with a 2.5-inch SATA SSD that functions as the system drive. Discard the 32GB mSATA SSD or replace it with a newer and larger one used for secondary storage.

Both of these options require more than just swapping out the hardware. They require setting the SATA controller to AHCI mode and reinstalling Windows. You can do this yourself but be aware that you can damage the file structure and make the system unbootable if you don't know what you're doing.

M.2 SSD

The M.2 SSD is much smaller than other common SSDs. It's about the size of a stick of gum. M.2 drives are attached to the motherboard via an M.2 socket and are typically removable. Because of their slim design and low power consumption, M.2 SSDs are generally used in tablets and ultrabooks.