Final answer:
Mainframe computers are part of the first generation of computers that emerged in the early 1950s. The UNIVAC I and the IBM 701 are notable examples of these early mainframes. These computers were characterized by their large size and use of vacuum tube technology.
Step-by-step explanation:
The question 'in which generation is the mainframe computer in' pertains to the history and development of computer technology, specifically the era in which mainframe computers belong. Mainframe computers, which were extremely powerful for their time, emerged in the early 1950s with systems like the UNIVAC I and the IBM 701. These systems are considered to be part of the first generation of computers, which were characterized by the use of vacuum tubes and were very large, requiring entire rooms for their circuits.
Over the decades, these computers played a dominant role in computing before the introduction of minicomputers in the 1970s. IBM was a major player during this era, controlling about 70% of the market by the late 1950s. The era of mainframe computers illustrates a technological and generational shift, indicating a kind of 'generation gap' between the generations who used these machines and those who use modern computing devices.