The rise of virtualization

The rise of virtualization

Operating systems were originally running directly on the hardware itself, and provided services to applications. With VM/CMS on System/370, IBM introduced the notion of virtual machine, where the operating system itself runs under the control of a hypervisor, instead of being in direct control of the hardware. VMware popularized this technology on personal computers. Over time, the line between virtual machines, monitors, and operating systems was blurred:

• Hypervisors grew more complex, gaining their own application programming interface^[5], memory management or file system ^[6]
• Virtualization becomes a key feature of operating systems, as exemplified by Hyper-V in Windows Server 2008 or HP Integrity Virtual Machines in HP-UX
• In some systems, such as POWER5 and POWER6-based servers from IBM, the hypervisor is no longer optional^[7]
• Applications have been re-designed to run directly on a virtual machine monitor^[8]

In many ways, virtual machine software today plays the role formerly held by the operating system, including managing the hardware resources (processor, memory, I/O devices), applying scheduling policies, or allowing system administrators to manage the system.