Understanding Program Types
A couple types of programs could be considered old in the context of this chapter:
- DOS programs: These programs were developed to run under various versions of the Disk Operating System (DOS) that was the precursor to Windows.
- 16-bit Windows programs: These Windows applications were written for Windows 98 and earlier versions of Windows.
What does “16-bit” mean? Three classes of Windows applications exist: 16-bit, 32-bit, and 64-bit. The number of bits indicates the maximum amount of addressable memory supported by the program. Table 39.1 indicates the differences.
Technology | Meaning | Memory Addresses |
16-bit | 216 | 65,536 |
32-bit | 232 | 4,294,967,296 |
64-bit | 264 | 18,446,744,073,709,600,000 |
Windows NT, Windows 2000, and Windows XP were all originally 32-bit operating systems. Windows XP was also offered in a 64-bit edition. Windows 98 and earlier were 16-bit operating systems. Windows Vista and Windows 7 were offered in two versions, 32-bit and 64-bit. Likewise, Windows 8 is available in 32-bit and 64-bit versions. Suffice it to say, the higher the bits, the more capable the operating system. For the purposes of this chapter, the key point is that you can run a program on the OS it was designed for or (possibly) on a later version, but you can’t go backwards. For example, you can run a 32-bit application on a 64-bit OS, but you can’t run a 64-bit program on a 32-bit OS.
DOS programs ...
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