(1) DOS operating system
DOS was originally developed as an operating system for the IBM PC, so its hardware platform requirements were minimal. Even with the higher version of DOS 6.22, it works with 640KB of memory, 60MB of hard disk, and 80286 microprocessors. DOS operating system is a single-user, single-task, character interface, and 16-bit operating system. As a result, its memory management is limited to the 640KB range. DOS comes under three different brands: MS-DOS from Microsoft, PC-DOS from IBM, and DR-DOS from Novell. All three DOS are compatible, but there are some differences.
(2) Windows operating system
Windows, the first windowing multitasking system released by Microsoft in November 1985, ushered in the era of the so-called graphical user interface (GUI) for PCS. In 1995, Microsoft introduced the Windows 95 operating system. In 1998, Microsoft introduced an improved version of Windows 98, Windows 95. One of the biggest characteristics of Windows 98 is the integration of Microsoft's Internet browser technology into Windows 98, making access to Internet resources as convenient as access to local hard disk, so as to better meet the needs of more and more people access to Internet resources. Windows 95 and Windows 98 are single-user, multi-task, 32-bit operating systems.
At the advent of the year 2000, Microsoft launched the Windows 2000 version. Not only does it take many of the best features of Windows 98 and Windows NT, but it is also an evolution of Windows 98 and Windows NT. After that, there will be no more single-user and web versions of Windows, enabling users to handle different transactions with the same, friendly operating system interface in the same operating system. Windows 2000 is a multi-user, multi-tasking operating system.
Now, Microsoft has introduced Windows XP. Windows XP USES the source code of Windows 2000 as the foundation, so that it has reliable stability, continue to maintain its security, reliability advantages. For the Internet age, Windows XP is more popular.
In 2014, Microsoft replaced Windows XP with Windows 7 and 8. Windows 7 and Windows 8 both have 64-bit versions, a significant improvement over XP. Windows 8 is primarily aimed at tablet devices. Windows 7 was designed to replace XP.

(3) UNIX system
The UNIX system was introduced in 1969, and was originally used on small and medium-sized computers. The first UNIX system to be ported to the 80286 microcomputer was called Xenix. Xenix has now developed into a very mature system, and the latest versions of Xenix are SCO UNIX and SCO CDT. The characteristic of UNIX system is short and delicate, system overhead is small, run fast. The current major versions are UNIX 3.2 V4.2 and ODT 3.0. UNIX is a popular system.
UNIX system is a multi-user system, generally requires more than 8MB of memory and a large capacity of hard disk, also suitable for high-end microcomputers.

(4) OS/2 system
OS/2 system is a new multitask operating system developed by PS/2 series machine. OS/2 overcomes the limitation of 640KB of main memory and has multi-tasking capabilities. In 1987, IBM launched the PS/2 Personal System/2 Personal computer in the fierce market competition. PS/2 series computers greatly break through the current PC system, using the microchannel bus MCA which is incompatible with other buses, and IBM designed most of the parts of the system itself, to prevent other companies from copying.
OS/2 features a graphical interface and is itself a 32-bit system that can handle not only 32-bit OS/2 application software, but also 16-bit DOS and Windows software. OS/2 systems typically require hardware with 4MB of memory and 100MB of hard disk or higher. If the hardware is more advanced, the system will run more stably.
Conclusion: for computer beginners, or to master the main Windows system, other systems may not have to pay attention to.