AWT uses native calls to the OS to draw widgets. (Heavyweight) But AWT is a lot more than just widgets and Swing still uses the AWT event queue, layout managers, etc.
Swing draws all of it's own widgets. (Lightweight)
JVM N JRE
No really a question for this forum...but...
The JRE is a collection of executables, JAR's and native libraries to run java applications. The JVM is the virtual machine that these applications run in. java.exe starts the JVM which runs the application.