Here we will check about workflow architecture in SharePoint 2013. Also you can check:
In SharePoint 2013 workflow is treated as a service. Now SharePoint workflows will not run in SharePoint servers, rather the execution will be handled by Windows Azure Workfl ow on a separate server.
SharePoint 2013 workflow supports Windows Workflow Foundation 4.0 and .NET Framework 4.5.
In SharePoint 2010, power users use SharePoint Designer to build declarative workflows and developers use Visual Studio to build programmatic workflows. But in SharePoint 2013 the focus is to build workflows declaratively.
In SharePoint 2010 all out of box workflows are declarative workflows and the new workflows you build either by using SharePoint Designer 2013 or Visual Studio 2013 will also be declarative.
Since all SharePoint 2013 workflows declarative, you can use sandboxed solutions
to deploy your workflow.
Microsoft recommends to build new workflows using the SharePoint 2013 workflow model and push the custom code to web services. Building a programmatic workflow all from scratch is still possible but is not recommended. SharePoint can’t host a programmatic workflow, and it has to be deployed to Windows
Azure Workflow as a non-SharePoint 2013 workflow.
SharePoint 2013 supports backward-compatibility, so existing SharePoint 2010 workflows can migrate to SharePoint 2013 without any problems. Also SharePoint 2013 workflows can call SharePoint 2010 workflows.
Windows Azure Workflow and Service Bus are available in Office 365 deployments.