Chapter 7: Virtual Machine I: Processing

page 192 in the book: (copy from the book)

Static: Static variables are mapped on addresses 16 to 255 of the host RAM. The VM translator can realize this mapping automatically, as follows. Each reference to static i in a VM program stored in file Foo.vm can be translated to the assembly symbol Foo.i. According to the Hack machine language specification (chapter 6), the Hack assembler will map these symbolic variables on the host RAM, starting at address 16. This convention will cause the static variables that appear in a VM program to be mapped on addresses 16 and onward, in the order in which they appear in the VM code. For example, suppose that a VM program starts with the code push constant 100, push constant 200, pop static 5, pop static 2. The translation scheme described above will cause static 5 and static 2 to be mapped on RAM addresses 16 and 17, respectively. This implementation of static variables is somewhat devious, but works well. It causes the static variables of different VM files to coexist without intermingling, since their generated FileName.i symbols have unique prefix file names. We note in closing that since the stack begins at address 256, the implementation limits the number of static variables in a Jack program to