How can one computer pretend to be many?
In 1967 IBM had one machine run fourteen at once, and cloud computing still rests on the same trick.
▶ Start the storyOne real computer can pretend to be many by running a layer of software, called a hypervisor, that creates virtual machines. A virtual machine is a software imitation of a whole computer, complete with its own operating system. The real computer is the host, each imitation is a guest, and the hypervisor shares out the hardware so that every guest feels it has a machine to itself.
Unlike an , a guest under a hypervisor executes most of its instructions directly on the real hardware. And Linux, Windows and macOS instances can all run side by side on one physical machine, isolated from one another.
Step 1: One real machine
The host, with real hardware
Step 2: Hypervisor
Creates and runs the virtual machines
Step 3: Guests, each with an OS
Linux, Windows and macOS can share one machine
Step 4: Privileged actions caught
In CP-40, the control program simulated them
The idea is older than most people think. It grew out of , where a computer switched quickly between users so that each seemed to have it to themselves. In January 1967 IBM's Cambridge Scientific Center put CP-40 into production use, built with MIT researchers on a specially modified IBM System/360 Model 40. It was the first operating system to offer complete virtualization, and it ran fourteen virtual machines at once.
Decades later the trick solved an economic problem. The average of a server in the early 2000s was 5 to 15%, so most of the hardware sat idle. Virtualization let a single server consolidate the work of several underused ones. That is why virtualization is the main enabling technology for cloud computing.
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Recap
A hypervisor makes one real computer look like many, each guest with its own operating system, mostly running directly on the real hardware.
💡 A trick to remember it · A hypervisor is an apartment-building manager: one building, many tenants, and each thinks the whole place is theirs.
Surprising fact · IBM's CP-40 ran fourteen virtual machines at once in 1967.
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No source, no claim. Every fact in this lesson (15 claims) cites at least one of these.