History of Virtualization and Architectural Evolution in Software Encode barcode 128 in Software History of Virtualization and Architectural Evolution

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Appendix use software ansi/aim code 128 integration todisplay code 128a on software barcode History of Virtualization and Architectural Evolution in which p rivileged instructions are suppressed and generate a program trap. In non-virtualized environments, this architecture protects system integrity by preventing malicious or buggy applications from issuing instructions that change machine state (such as enabling or disabling interrupts, or changing memory mapping) and potentially crashing the system or creating security exposures. This mechanism works differently in virtual machine environments, as guest operating systems are expected to execute privileged instructions and have them function in the same way as they would on the real machine.

An attempt by a guest operating system to execute a privileged instruction generates a program trap to the hypervisor, which then emulates the instruction (in software) solely in the context of the virtual machine. This behavior has performance implications that will be discussed later in this appendix. This paradigm supports the Popek and Goldberg properties and is still used by hypervisors.

Note that the x86 architecture does not satisfy the trap and execute virtualization described by Popek and Goldberg. Instead, x86 virtual machines can tell that they have been deprivileged, and some privileged instructions (such as popf) are suppressed but do not cause a trap. The x86 hypervisors handle this situation in different ways: VMware performs binary translation to replace these instructions with code that manipulates guest state without privileged instructions, or with a call to the hypervisor, whereas Xen uses paravirtualization to eliminate use of privileged instructions.

. Virtual Machines Emerge from the Laboratory CP-40 was ported to the System/360 model 67, IBM s rst production virtual memory computer, and renamed CP/67. The 360/67 was intended to be IBM s of cial time-sharing system, as IBM began to adopt this style of computing as an addition to OS/360 s batch workloads. A new and ambitious operating system, TSS/360, was written for it.

While TSS/360 introduced novel concepts, it was burdened by delays and had reliability and performance problems. CP/67, which had a simpler design and was based on virtual machines, began to be used for time sharing and program development using a simple interactive single-user OS called the Cambridge Monitor System (CMS). Instead of a single OS instance shared by multiple users, as in CTSS, Multics, and UNIX, CMS provided a lightweight single-user OS instance for each user, and exploited a separation of functions with the hypervisor for resource management and access control.

This strategy permitted use of a very simple design: a single at per-user address space, a non-multitasking program model (multitasking was provided by overlapped execution of multiple CMS users), a minimal permission model (all security was implemented in the virtual machine monitor), and a. A BRIEF HISTORY OF SYSTEM VIRTUALIZATION basic non- hierarchical le system (each user had virtual disks called minidisks, implemented by cylinder extents on physical disks). This design a simple OS leveraging services from the hypervisor permitted the system to have a small memory footprint and a short instruction-path length well suited for providing short response times on the computers of the day. The idea of a lightweight virtualization environment can be seen in unrelated later systems such as Solaris Containers that shift heavy lifting to the hosting environment.

This design pattern was also deployed for non-interactive users: CMS guests running disconnected from a terminal were used to implement service virtual machines a precursor to UNIX daemons for scheduled or event-driven work. Soon, a signi cant client base used CP/67 virtual machines and interactive computing. It also became clear that the extremely complex (for the times) OS/360 would be shipped too late to satisfy many customers needs, and would require more memory than was available on many 360 models.

As a result, the 360 used several incompatible operating systems (DOS/360, OS/360) with different programming conventions. Several institutions began to use CP/67 to run multiple-guest OS instances on the same physical machine, so the same machine could be shared by different workloads. Even though deployment of virtual machines remained limited, technology and business drivers for virtual machines had clearly arrived by the early 1970s.

At this point, the virtual machines concept had already taken on its de ning role running multiple OS instances on the same physical server..
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