Network Operating System

• Examples: UNIX, Windows
• Built-in networking capability and can be used to access remote resources.
• Access is network-transparent for some types of resource.
  • Example: distributed file system such as NFS, users have network-transparent access to files.
• Nodes retain autonomy in managing their own processing resources. 
• User can remotely log into another computer and run processes there. 
• OS manages processes running at its own node, but does not manage processes across the nodes. 
• There are multiple system images, one per node. 

Distributed operating system

• Users are never concerned with where their programs run, or the location of any resources.
• OS has control over all the nodes in the system
• It transparently locates new processes at whatever node suits its scheduling policies. 

Middleware and network operating system

• There are no distributed operating system in general use. 
• Two main reasons
  • Users have much invested in their application software, which often meets their current problem-solving needs
  • Users tend to prefer to have a degree of autonomy for their machines. 
• These combination provides an acceptable balance between the requirement for autonomy and network transparent resource access on the other.