programming-for-dummies

662
Cross-Platform Programming
entire program from scratch for a different operating system, but this
process isn’t trivial.
Create a program that can run on three different operating systems, and now you
have to worry about maintaining and fixing problems with your program on three
different operating systems. It’s possible for your program to work perfectly
under Linux, but crash under Windows and the Macintosh. The more operating
systems your program supports, the greater the complexity in getting your program
to work right under all these different operating systems.
Virtual machines
The main advantage of cross-platform compilers is that they compile programs
directly into machine language for each specific operating system,
which makes your programs run as fast as possible. With today’s faster computers,
speed is rarely as important as in the old days when slow programs
could literally take hours to perform a single task.
Because speed isn’t as crucial as in the past, computer scientists have created
another way to create cross-platform programs known as virtual machines.
Rather than compile a program for a specific processor, virtual machine programming
languages compile programs to a generic format (called bytecode,
pseudocode, or p-code) that can run on a virtual machine. This virtual machine,
running on different operating systems, essentially tricks the program into
thinking it’s running on a single computer, as shown in Figure 5-2.
Source code
Compiler
Figure 5-2:
A virtual
machine
lets a
program run
on multiple
operating
systems.
Microsoft
Windows
Virtual Machine
Mac OS X
Linux