1. The only problem was that the aditional program instructions were very complex and time-consuming.

2. They were «complex» and «time-consuming» because they had to provide instructions that told the computer how to use devices.

3. The basic functions of operating system are to control and manage the use of hardware devices and to provide disc management.

4. It means Disc Operating System.

5. Microsoft developed the first version of DOS operating system. The purpose was to create a program that would control and manage the use of hardware devices and to provide disc management. The new operational system was successful.

6. PC-DOS  is licensed DOS from Microsoft for use on the PC and  MS-DOS is an abbreviation for Microsoft DOS.

7. The abbreviation NT stands for New Technology. NT is DOS-compatible. The basic requirements for NT are 386 processor or greater and 8 MB of RAM.

8. IBM is the developer of OS/2.

9. UNIX is not DOS compatible, but it allows several users to sumultaneously run the program they need.

10.The special features of Windows 95, Win­dows 98, Windows 2000 are the following: they all have the most popular user oriented system with an interface and multitasking capabilities, they are DOS compatible. Windows 95 requires 486 processor with 16 megabytes of RAM or Pentium 75-90 with 40 megabytes of free hard disk space.