The scope of a variable refers to the?

Portion of code in which the variable may be meaningful.

What are the important ways in which windows operating system is different from DOS?

Windows is a multi-threaded operating system. Multiple threads are executed on time sharing basis. Thus while one activity is going on in a window another activity may appear to be going on in another window simultaneously. Windows use graphical user interface. Windows run over the DOS layers.
DOS is a single threaded operating system. Only one activity is done at a time. It uses character user interface. Modern windows support advanced file systems.

What is BIOS in DOS?

BIOS is a collection of program stored in hardware ROM. BIOS contain device drivers for standard devices so that DOS could just call them to do I/O BIOS is located at the top of the address space. BIOS contain calls to read and write from absolute disk addresses and to read characters from keyboard and write to screen kernal access BIOS services by making procedure calls to io.sys instead of using interrupts to ROM. The file io.sys is loaded immediately after the computer is booted. BIOS also contain a rich collection of routines which can be accessed by user programs through software interrupts.

What is Copy Sales *.Data?

This command copy all files whose name start with SALES and extension DATA under root directory.