The development and evolution of modern computing has, in many ways, been facilitated by the power of logical abstraction. Early computers were manually programmed by slow and tedious input of machine instructions into the computers' memories. Over time, assembly-language programs and assemblers were developed in order to provide a level of abstraction, namely assembly-language programs, above the machine-instruction hardware-interface level, to allow programmers to more rapidly and accurately develop programs. Assembly-language-based operations are more easily encoded by human programmers than machine-instruction-based operations, and assemblers provided additional features, including assembly directives, routine calls, and a logical framework for program development. The development of operating systems provided yet another type of abstraction that provided programmers with logical, easy-to-understand system-call interfaces to computer-hardware functionality. As operating systems developed, additional internal levels of abstraction were created within operating systems, including virtual memory, implemented by operating-system paging of memory pages between electronic memory and mass-storage devices, which provided easy-to-use, linear memory-address spaces much larger than could be provided by the hardware memory of computer systems. Additional levels of abstractions were created in the programming-language domain, with compilers developed for a wide variety of compiled languages that greatly advanced the ease of programming and the number and capabilities of programming tools with respect those provided by assemblers and assembly languages. Higher-level scripting languages and special-purpose interpreted languages provided even higher levels of abstraction and greater ease of application development in particular areas. Similarly, block-based and sector-based interfaces to mass-storage devices have been abstracted through many levels of abstraction to modern database management systems, which provide for high-available and fault-tolerant storage of structured data that can be analyzed, interpreted, and manipulated through powerful high-level query languages.
In many ways a modern computer system can be thought of as many different levels of abstractions along many different, often interdependent, dimensions. More recently, powerful new levels of abstraction have been developed with respect to virtual machines, which provide virtual execution environments for application programs and operating systems. Virtual-machine technology essentially abstracts the hardware resources and interfaces of a computer system on behalf of multiple virtual machines, each comprising one or more application programs and an operating system. Even more recently, the emergence of cloud computing services can provide abstract interfaces to enormous collections of geographically dispersed data centers, allowing computational service providers to develop and deploy complex Internet-based services that execute on tens or hundreds of physical servers through abstract cloud-computing interfaces.
While virtualization technologies have been used for many years to great advantage in a variety of different settings and applications, there remain many opportunities for the design and development of new features, facilities, and capabilities within virtualization layers, virtual machines, and other related virtualization technologies. Designers, developers, and vendors of virtualization technologies continue to seek new features, facilities, and capabilities to provide increasing ease of installation, ease of use, and various different desired functionalities and capabilities within virtualization products.