Difference Between Sequential Workflow & State machine workflow?

Sequential workflow

A sequential workflow represents a series of steps. The steps are performed one after another until the last activity is completed. Sequential workflows are always strictly sequential in their execution. Because they can receive external events, and include parallel logic flows, the exact order of execution may vary. The following illustration shows an example of a sequential workflow.

The sequential process will look like this: 

State machine workflow

A state machine workflow represents a set of states, transitions, and actions. The steps in a state machine workflow execute asynchronously. This means that they are not necessarily performed one after another, but instead are triggered by actions and states. One state is assigned as the start state, and then, based on an event, a transition is made to another state. The state machine can have a final state that determines the end of the workflow. The following diagram shows an example of a state machine workflow.

The state machine process will be: 

Referenced Links

MSDN Link

https://www.nothingbutsharepoint.com/sites/eusp/Pages/SharePoint-State-machine-or-sequential-workflows-What-is-the-future-of-business-processes.aspx