Around 1985 or so, the IBM PC running MS-DOS was becoming popular both as personal and business computing platforms. The 8086 processor was real mode only and was designed only for single processing, single use. Though the 80286, then the 80386, could handle protected mode operation at the hardware level, the Operating System these systems ran was generally still MS-DOS running in real mode. Protected mode systems were available at that time, but were not in common use. The advent of MS Windows brought basic multitasking and protected mode to the PC, but the basic Windows design remained single user. Typical home user Windows systems did not become truly multi-user capable until the release of Windows 2000.
Though almost all current releases of Windows are multi-user, Windows seems like it has difficulty shaking its single user roots. Some versions of Windows have limits on the number of simultaneous connections or sessions that are supported.
Linux on the other hand was multi-user from the start. Linux, which began around 1991, was an evolution of an Operating System called Minics which in turn was written to teach Operating System Design. The core functionality loosely followed that of Unix, which was 20 years mature at that time. This is key to understand some of the core differences between Linux and Windows: Linux utilized the ideas of a multi-user, heavily networked, strongly tested OS with a 20 year history.