New to Java

I installed - window on line installation Multi-language-jdk-6-windsows-i586-iftw.exe-361.62 size. The file was installed to C:\Program Files\Java\jdk1.6.0\ and C:\Program Files\Java\jre1.6.0\ --size8.4MB.
1Before installation file size for jdk-6-windows-i.586-iftw.exe was 361.62. Why after installation size is showing 8.4MB?
2. Though file specs was jdk-6-windows----how come after installation file jre1.6.0 appear??
3In Command Prompt, while i press Enter on following command
C:\>Program Files\Java\jdk1.6.0_<version>\bin\javac HelloWorldApp.java, i am getting -- >
"The system cannot find the file specified.
What is the exat locationof file?
4 Suffix b105 preceedes jdk1.6.0 & jre1.6.0.
What does b105 stand for?
damp.
Source code is as follows
Class HelloWorldApp {
public static void main((String[] args) {
System.out.println("Hello World!"); //
Display the String
}
}