Tower servers are the largest, consisting of a vertical enclosure much like a desktop CPU tower. They require high cabling but don't need a lot of maintenance. This type of server is designed to fit underneath a desk and offers basic performance. It is relatively compact and inexpensive.
Rack servers are smaller than tower servers, and are designed to be positioned in a bay. This means you can stack multiple rack servers on top of each other. The bay can accommodate all the servers, storage devices, security and network appliances you need in a single, convenient space.
One of the benefits of rack servers is that having all components in one place allows the formation of a type of data center, providing the flexibility to install several servers in the same bay. They are, however, more expensive, which makes them better suited for medium-size businesses.
Blade servers are the smallest member of the server family. They are slim and compact and can be placed vertically into a specially designed case. Their downside is that they also offer the least power. Since they can be stacked vertically, you can add multiple servers, which makes them best for medium- to larger-sized companies.
The main difference between a tower server and a blade or rack is that tower servers provide functionality for small businesses. Data centers may need multiple servers snuggled into one room, whereas implementing a tower server is not different from having another computer in the office.