What is the difference between OwinStartup and PreApplicationStartMethod?

Hi

I have a project and I see that the classes with these attributes load in the beginning of the app.

I would like to know the difference...

For instance..I have the code...

[assembly: OwinStartup(typeof(Centenario.Proy.Service.Rest.MainContext.Startup))]
namespace Centenario.Proy.Service.Rest.MainContext
{
    public class Startup
    {
        public void Configuration(IAppBuilder app)
        {
            var httpConfig = new HttpConfiguration();
            var cors = new EnableCorsAttribute("*", "*", "*");
            InitializeContainer.Start(httpConfig);
            httpConfig.EnableCors(cors);
            SignalRConfig.Register(app, cors);
            WebApiConfig.Register(httpConfig);
            RouteConfig.RegisterRoutes(RouteTable.Routes);
            app.UseWebApi(httpConfig);


            /***********21/05/2019**********************/
            //var config = new HubConfiguration();
            //config.EnableJSONP = true;
            //app.UseCors(CorsOptions.AllowAll);
            //app.MapSignalR(config);
            /******************************/

            // Any connection or hub wire up and configuration should go here
            //app.MapSignalR();
        }
    }

And the code,,,

[assembly: PreApplicationStartMethod(typeof(SwaggerConfig), "Register")]

namespace Centenario.Proy.Service.Rest.MainContext
{
    public class SwaggerConfig
    {
        public static void Register()
        {
            var thisAssembly = typeof(SwaggerConfig).Assembly;

            GlobalConfiguration.Configuration
                .EnableSwagger(c =>
                    {
                        // By default, the service root url is inferred from the request used to access the docs.
                        // However, there may be situations (e.g. proxy and load-balanced environments) where this does not
                        // resolve correctly.