Most important things to consider when buying a web server and other hardware:

Hard drive Size
Normal web users does not take up much space at all, but if your customers are depending on e-commerce stores and taking orders, the storage must be of considerable size in order to store the database information.
Each transaction is grouped with customer information like name, address and credit card.

Platform
The most chosen category of web server software is Apache. It's constantly updated for user's benefit, and it's the most economical choice because it's free. However, it isn't backed like Microsoft Internet Information Server (IIS). IIS only works with NT-based server systems, since NT is Microsoft. However, if you're concerned about safety, it has crash protection.

Speed and Performance
Traffic slows down the web server's processor, It’s therefore of utter importance that the web server has enough memory and fast processor. Otherwise traffic can't get through. Low quality memory and slow-speed processors can greatly affect the performance of even the best servers.

Ability to scale
Another aspect is user load. As a providers business grows, more storage is needed. That means more hard drives and more RAM memory to add. The web server must be able to expand.

Manageability
For you as a web hosting customer there is nothing more frustrating when your website goes down. This could be the result of a difficult server to manage. Replacing a crashed hard drive or malfunctioning CD-ROM must be easy for any network administrator.

Types of servers
There are basically four different web server hardware options to choose from:

-Pre-built rack server units.
Most network administrator’s wet dream. Not easy to replace the OS or installing any new software, but for those who can live with these drawbacks, there are many benefits. How about taking up less space, producing less heat and cost less?

-Pre-build tower server
Most administrators go with this option. Why? Because it is easy. They know they're getting a well-designed server with proven technology. This in turn means big brand vendors, good warranties, high-level of service and before mentioned well proved technology.

-Cheap custom-built server
Quality minded network administrators might wave of this alternative as pure nonsense due to its low-end processors and IDE hard drives. But for web hosting companies that have to survive on a shoe string budget, this is a great option. In the end it's always a cost-benefit analysis. Sooner or later these parts will also need to be replaced, costing even more money in the long run.

Expensive custom-built server
This alternative doesn't come with warranties so if all hell break loose you are on your own. On the other hand, a custom built machine will endure even the toughest challenges. You can think of it as a pre-built server with a lot of added options. Building a machine like this will take long time and cost serious money.