What is the Difference between class library and Portable Class library in .Net?

Question

What is the difference between <asp:Panel > and <asp:PlaceHolder > in ASP.NET? When should you use one over the other?

Answer 1

Class library:

The .NET Framework class library is a library of classes, interfaces, and value types that are included in the Microsoft .NET Framework SDK. This library provides access to system functionality and is designed to be the foundation on which .NET Framework applications, components, and controls are built.

Portable Class Library:

The Portable Class Library project enables you to write and build managed assemblies that work on more than one .NET Framework platform. You can create classes that contain code you wish to share across many projects, such as shared business logic, and then reference those classes from different types of projects.