Since I work at Gartner, I use Gartner’s hosting definitions when I talk about the market. We classify the hosting market into four segments: Colocation, Shared Hosting, Simple Managed Hosting, and Complex Managed Hosting. Colocation is unmanaged colocation (“ping, power, pipe”). Shared Hosting is mass-market shared-infrastructure hosting. The Simple Managed segment is typified by management only up to the OS layer, and simple architectures (usually just 1 or 2 servers). The Complex Managed segment is everything else. Cloud infrastructure services span the latter three categories, depending on what they are.

Sample Colocation Providers:

• Equinix (carrier-neutral data centers)
• AT&T (carrier)
• SAVVIS (has a network but doesn’t require its use)
• Peak 10 (regional provider)
• Hurricane Electric (local provider)

Sample Shared Hosting Providers:

• Yahoo! (small business portal)
• GoDaddy (domain registrar)
• 1&1 Internet (shared hosting-focused provider)
• NTT Verio (mass-market hosting, including wholesaling)

Sample Simple Managed Hosting Providers:

• The Planet
• Rackspace (its “Managed” line of business)
• Hostway

Sample Complex Managed Hosting Providers:

• AT&T
• SAVVIS
• Terremark
• Rackspace (its “Intensive” line of business)

My core Gartner notes on the subject (you’ll need to be a client to see these, sorry):

• Market Overview
• Market Forecast
• Magic Quadrant (vendor rating)