Timeline of virtualization technologies: Difference between revisions

Revision as of 14:35, 23 May 2024

Revision as of 14:36, 23 May 2024

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==== Application virtualization ====

[[Application virtualization]] solutions such as [[VMware ThinApp]], [[Softricity]], and Trigence attempt to separate application-specific files and settings from the host operating system, thus allowing them to run in more-or-less isolated sandboxes without installation and without the memory and disk overhead of full machine virtualization. Application virtualization is tightly tied to the host OS and thus does not translate to other operating systems or hardware. VMware ThinApp and Softricity are Intel Windows centric, while Trigence supports [[Linux]] and [[Solaris network virtualization and resource control|Solaris]]. Unlike machine virtualization, Application virtualization does not use code emulation or translation so CPU-related benchmarks run with no changes, though filesystem benchmarks may experience some performance degradation. On Windows, VMware ThinApp and Softricity essentially work by intercepting filesystem and registry requests by an application and redirecting those requests to a preinstalled isolated sandbox, thus allowing the application to run without installation or changes to the local PC. Though VMware ThinApp and Softricity both began independent development around 1998, behind the scenes VMware ThinApp and Softricity are implemented using different techniques:

* VMware ThinApp works by packaging an application into a single "packaged" EXE which includes the runtime plus the application data files and registry. VMware ThinApp's runtime is loaded by Windows as a normal Windows application, from there the runtime replaces the Windows loader, filesystem, and registry for the target application and presents a merged image of the host PC as if the application had been previously installed. VMware ThinApp replaces all related API functions for the host application, for example the ReadFile API supplied to the application must pass through VMware ThinApp before it reaches the operating system. If the application is reading a virtual file, VMware ThinApp handles the request itself otherwise the request will be passed on to the operating system. Because VMware ThinApp is implemented in user-mode without device drivers and it does not have a client that is preinstalled, applications can run directly from USB Flash or network shares without previously needing elevated security privileges.

* Softricity (acquired by Microsoft) operates on a similar principle using device drivers to intercept file requests in ring0 at a level closer to the operating system. Softricity installs a client in Administrator mode which can then be accessed by restricted users on the machine. An advantage of virtualizing at the kernel level is the Windows Loader (responsible for loading [[.exe|EXE]] and [[Dynamic-link library|DLL]] files) does not need to be re-implemented and greater application compatibility can be achieved with less work (Softricity claims to support most major applications). A disadvantage of ring0 implementation is that it requires elevated security privileges to be installed and crashes or security defects can occur system-wide rather than being isolated to a specific application.