OS202
Free software
Free software (or libre software) is computer software distributed under terms that allow users to run the software for any purpose as well as to study, change, and distribute it and any adapted versions.
Free software is a matter of liberty, not price: users and computer programmers are free to do what they want with their copies of a free software (including profiting from them) regardless of how much is paid to obtain the program.
Computer programs are deemed “free” if they give both programmers and end-users ultimate control over the software and, subsequently, over their devices.
Open Source Software
Open-source software (OSS) is a type of computer software in which source code is released under a license in which the copyright holder grants users the rights to use, study, change, and distribute the software to anyone and for any purpose.
Open-source software may be developed in a collaborative public manner. Open-source software is a prominent example of open collaboration.
Freeware
Freeware is software, most often proprietary, that is distributed at no monetary cost to the end user. There is no agreed-upon set of rights, license, or EULA that defines freeware unambiguously; every publisher defines its own rules for the freeware it offers.
For instance, modification, redistribution by third parties, and reverse engineering without the author’s permission are permitted by some publishers but prohibited by others.
Open Source vs Freeware vs Free Software
Open-source license criteria focus on the availability of the source code and the ability to modify and share it, while free software and public domain focus on the user’s freedom to use the program, to modify it, and to share it.
Freeware (examples are Skype and Adobe Acrobat), in its term, is mostly aiming commercial goals and potential monetization often used as a “freemium” product.
Virtual Infrastucture
Virtual infrastructre lets us share physical resources of multiple machines across entire infrastructure.
A virtual machiens lets us to share the resources of a single physical comptuter across multiple virtual machines for maximum efficiency.
Rescources are shared across multiple virtual machines and applications.
Permissive
Permissive licenses place minimal restrictions on software users.
Often they only require that the original creators are attributed in any distribution or derivative of the software or source code.
Copyleft
For software creators who want to guarantee unlimited open-source access to their work employ the concept of copyleft.
Copyleft uses copyright’s legal framework to ensure continued open access to software and its source code.
Hypervisor
A hypervisor (or virtual machine monitor, VMM, virtualizer) is computer software, firmware or hardware that creates and runs virtual machines.
A computer on which a hypervisor runs one or more virtual machines is called a host machine, and each virtual machine is called a guest machine.
virtual Box is one of the example of Hypervisor.
Virtual Memory
Virtual memory is a memory management technique where secondary memory can be used as if it were a part of the main memory.
Virtual memory uses hardware and software to allow a computer to compensate for physical memory shortages, by temporarily transferring data from random access memory (RAM) to disk storage.
In essence, virtual memory allows a computer to treat secondary memory as though it were the main memory.
Emulation vs Virtualization
When a device is being emulated, a software-based construct has replaced a hardware component. Its possible to run a complete virtual machine on an emulated server.
However, virtualization makes it possible for that virtual machine to run directly on the underlying hardware, without needing to impose an emulation tax (the processing cycles needed to emulate the hardware).