<center>https://www.webdesignerdepot.com/cdn-origin/uploads/vintage_tech/IBM360Fam.jpg</center>

While companies still use massive mainframe systems not too disimilar from the picture shown above these days a lot of companies opt to use cloud services like Amazon's AWS or Microsoft's AZURE. 

And even though mainframes still exist, they generally don’t take up entire rooms or store information on magnetic tape. 

>Mainframe computers (colloquially referred to as "big iron"[1]) are computers used primarily by large organizations for critical applications; bulk data processing, such as census, industry and consumer statistics, enterprise resource planning; and transaction processing. They are larger and have more processing power than some other classes of computers: minicomputers, servers, workstations, and personal computers. 

https://upload.wikimedia.org/wikipedia/commons/thumb/4/45/IBM_z13_and_LinuxONE_Rockhopper.jpg/440px-IBM_z13_and_LinuxONE_Rockhopper.jpg

>The term originally referred to the large cabinets called "main frames" that housed the central processing unit and main memory of early computers.[2][3] Later, the term was used to distinguish high-end commercial machines from less powerful units.[4] Most large-scale computer system architectures were established in the 1960s, but continue to evolve. Mainframe computers are often used as servers. 

Is my laptop a mainframe? No. 

Is a large high-end commercial machine considered to be a mainframe? Yes, quite possibly. 

Although mainframes themselves exist the way we process and store data has fundamentally changed with cloud taking over the responsibility of handling many of these tasks and ultimately reducing costs for companies due to large economies of scale that can be incorporated using this setup. 

The old days of having big clunky machines that store data on tape have long gone fortunately so the picture above has very little in common with today's mainframe systems currently in use. 

Source: 

Wikipedia