Parallel Start in Websphere Application Server ND 7/8/8.5

Select this field to start the server on multiple threads. This might shorten the startup time.
Specifies that you want the server components, services, and applications to start in parallel rather than sequentially.The default setting for this option is true, which indicates that when the server starts, the server components, services, and applications start on multiple threads. Setting this option to false specifies that when the server starts, the server components, services, and applications start on a single thread, which might lengthen start-up time.

The order in which the applications start depends on the weights that you assign to them. Applications that have the same weight start in parallel.To set the weight of an application, in the administrative console, click Applications > Application Types > WebSphere enterprise applications > application_name > Startup behavior, and then specify an appropriate value in the Startup order field. The more important an application is, the lower the startup order value should be. For example, you might specify a startup order value of 1 for your most important application, and a value of 2 for the next most important application. You might then specify a startup order of 3 for the next four applications because you want all four of those applications to start in parallel.

Start components as needed ;

Select this property if you want the server components started as they are needed by an application that is running on this server.
When this property is selected, server components are dynamically started as they are needed. When this property is not selected, all of the server components are started during the server startup process. Therefore, selecting this option can improve startup time, and reduce the memory footprint of the server, because fewer components are started during the startup process.
Starting components as they are needed is most effective if all of the applications, that are deployed on the server, are of the same type. For example, using this option works better if all of your applications are Web applications that use servlets, and JavaServer Pages (JSP). This option works less effectively if your applications use servlets, JSPs and Enterprise JavaBeans (EJB).