A 32-bit processor is one that generally supports a word size of 2**32, where the constant "maxint" has the value 2**32-1, or 4,294,967,295. It also means that programs and data spaces can be much larger than on the older 16-bit machines. It also means that data space is much smaller than on current (2020) 64 bit machines.
Examples of 32-bit processors include
- X86 microcomputer (WINTEL architecture)
- Hewlett-Packard VAX mainframe/minicomputer
- IBM 360/370 Mainframe series (now known as Z-series)
- Motorola 68000 series (Macintosh)
The 32-bit processor type on the X86 (80386, 80486, Pentium) added additional features including enhanced multiprocessing, which is why you can have several programs running simultaneously, and task-protection, which (supposedly) means that if one program crashes it doesn't take the whole system down with it. This behaviour works more consistently on Linux than on Windows.
Some 32-bit processors (X86) are enhancements of 16-bit processors, and generally can run 16-bit applications. The reverse, however, is not true; 32-bit code cannot run on a machine smaller than 32 bits.