docs: update virt/lexicon

virt/lexicon.md

@@ -2,7 +2,7 @@
 title: Lexicon
 description: 
 published: true
-date: 2022-01-12T15:43:12.102Z
+date: 2022-01-14T10:47:23.635Z
 tags: 
 editor: markdown
 dateCreated: 2021-11-13T11:58:43.776Z
@@ -12,84 +12,53 @@ dateCreated: 2021-11-13T11:58:43.776Z
 
 ## Emulator
 
-Emulators or virtualizers are software that provide material components
+Emulators or virtualizers are software that provide material components similar to physical hardware, but that are made of computer code instead of silicon, -- virtual hardware --, such as virtual floppy disks.
-similar to physical hardware, but that are made of computer code instead
-of silicon, -- virtual hardware --, such as virtual floppy disks.
 
-QEMU is a popular emulator that can act as a simulator or virtual
+QEMU is a popular emulator that can act as a simulator or virtual machine monitor. In the latter case, it can leverage hardware acceleration,
-machine monitor. In the latter case, it can leverage hardware
-acceleration,
 
 ## Hardware-assisted virtualization
 
-Hardware-assisted virtualization is a feature of certain computer
+Hardware-assisted virtualization is a feature of certain computer hardware made to take advantage of virtualization.
-hardware made to take advantage of virtualization.
 
-Such hardware reduces the overheads associated with virtualization and
+Such hardware reduces the overheads associated with virtualization and is thus key to unlocking near-native performance for virtual machines.
-is thus key to unlocking near-native performance for virtual machines.
+
-In other words, hardware-assisted virtualization translates into better
+In other words, hardware-assisted virtualization translates into better performance for virtualized workloads, significantly reducing the gap in performance between a virtual machine and a physical one.
-performance for virtualized workloads, significantly reducing the gap in
-performance between a virtual machine and a physical one.
 
 ## Nested-virtualization
 
-Nested-virtualization refers to the ability to run a virtual machine
+Nested-virtualization refers to the ability to run a virtual machine inside another virtual machine.
-inside another virtual machine.
 
 ## Virtualization
 
-Most computers are made of hardware and software. By analogy, the brain
+Most computers are made of hardware and software. By analogy, the brain that animates the cells to control a body can be thought as the operating system that controls components of its body.
-that animates the cells to control a body can be thought as the
-operating system that controls components of its body.
 
-Virtualization can be defined as the ability to run a software-based
+Virtualization can be defined as the ability to run a software-based computer inside a physical computer. It is a set of computer-related techniques that make it possible to create replicas of computer hardware out of computer code. Those replicas are often referred to as virtual
-computer inside a physical computer. , It is a set of computer-related
-techniques that make it possible to create replicas of computer hardware
-out of computer code. Those replicas are often referred to as virtual
 machines.
 
 There are roughly three types of virtualization:
 
-*   **Simulation or emulation**: when a computer is fully emulated and
+*   **Simulation or emulation**: when a computer is fully emulated and can be made to look like any device to an operating system
-    can be made to look like any device to an operating system
+*   **Partition**: when computer resources are split such that each operating system can only see a subset of available hardware resources
-*   **Partition**: when computer resources are split such that each
+*   **Paravirtualization**: when both hardware and software-assisted virtualization is being used. In this case, the guest is aware that     it is running in the virtualized environment, and acts accordingly.
-    operating system can only see a subset of available hardware
-    resources
-*   **Paravirtualization**: when both hardware and software-assisted
-    virtualization is being used. In this case, the guest is aware that
-    it is running in the virtualized environment, and acts accordingly.
 
-Virtualization is used to better isolate resources on a physical
+Virtualization is used to better isolate resources on a physical computer and to distribute them across various workloads, enabling better use of resources through consolidation. For instance, with virtualization, multiple operating systems can run concurrently on a physical machine.
-computer and to distribute them across various workloads, enabling
-better use of resources through consolidation. For instance, with
-virtualization, multiple operating systems can run concurrently on a
-physical machine.
 
 ## Hypervisor
 
-A hypervisor is an operating system or firmware that is designed to run
+A hypervisor is an operating system or firmware that is designed to run guest systems: it handles scheduling, execution of hyper privileged instructions, memory management and over-commitment, and provides drivers for physical devices.
-guest systems: it handles scheduling, execution of hyper privileged
-instructions, memory management and over-commitment, and provides
-drivers for physical devices.
 
-The Virtual Machine Monitor (VMM) is a software that runs on top of the
+The Virtual Machine Monitor (VMM) is a software that runs on top of the hypervisor and manages the life cycle of a virtual machine. It provides device models for emulated devices and implements tasks such as start, suspend, migrate, and stop virtual machines.
-hypervisor and manages the life cycle of a virtual machine. It provides
-device models for emulated devices and implements tasks such as start,
-suspend, migrate, and stop virtual machines.
 
-The hypervisor and VMM work in tandem with emulators, which provide them
+The hypervisor and VMM work in tandem with emulators, which provide them virtual hardware.
-virtual hardware.
 
-As of 2021, there are two major open-source hypervisor that are both are
+As of 2021, there are two major open-source hypervisor that are both are able to leverage hardware-assisted virtualization:
-able to leverage hardware-assisted virtualization:
 
 -   Xen (2003)
 -   Kernel-based Virtual Machine (KVM) module for Linux (2007)
 
 ## Device
 
-Devices are computer components that can be attached to machines. They
+Devices are computer components that can be attached to machines. They can be classified in two ways : physical or emulated.
-can be classified in two ways : physical or emulated.
 
 | | Physical hardware | Emulated: model-based | Emulated: paravirtual |
 | :- | :-: | :-: | :-: |
@@ -98,59 +67,27 @@ can be classified in two ways : physical or emulated.
 
 *   Physical
 
-    *   Physical components refer to devices that can be attached to a
+    *   Physical components refer to devices that can be attached to a system. For instance, a dedicated physical graphics card attached to a physical system can be directly attached to a virtual machine, which then becomes responsible for managing it, a technique called *passthrough*. The PCI-SIG standards provide IOMMU-related specifications to allow a host operating system to not have a driver for a particular device and passthrough the device to the guest. The guest will have a device with nearly native performance, and use the standard vendor's drivers for the device.
-        system. For instance, a dedicated physical graphics card
+    *   The PCI-SIG standards also provide a way to partition compatible devices using so-called Virtual Functions (VFs). In this case, the host manages the way a physical device is used by the guest. Both host and guest must have specific device drivers. It offers nearly native performance.
-        attached to a physical system can be directly attached to a
-        virtual machine, which then becomes responsible for managing it,
-        a technique called *passthrough*. The PCI-SIG standards provide
-        IOMMU-related specifications to allow a host operating system to
-        not have a driver for a particular device and passthrough
-        the device to the guest. The guest will have a device with
-        nearly native performance, and use the standard vendor's drivers
-        for the device.
-    *   The PCI-SIG standards also provide a way to partition compatible
-        devices using so-called Virtual Functions (VFs). In this case,
-        the host manages the way a physical device is used by the guest.
-        Both host and guest must have specific device drivers. It offers
-        nearly native performance.
 
 *   Emulated
 
     *   Model-based
 
-        *   Model-based emulated hardware are designed after real
+        *   Model-based emulated hardware are designed after real devices, but are made out of computer code, not silicon. The i440fx and Q35 chipsets are both instances of emulated hardware. This is the slowest (but most compatible) way to provide a device to a guest. An emulated GPU is not going to be fast enough in an emulated mode to do 3D rendering.
-            devices, but are made out of computer code, not silicon. The
-            i440fx and Q35 chipsets are both instances of emulated
-            hardware. This is the slowest (but most compatible) way to
-            provide a device to a guest. An emulated GPU is not going to
-            be fast enough in an emulated mode to do 3D rendering.
 
     *   Paravirtual
 
-        *   Paravirtual hardware, also known as paravirtualized Virtual
+        *   Paravirtual hardware, also known as paravirtualized Virtual I/O devices or simply virtio, are also made out of computer code. Contrary to emulated hardware, they function as a generic piece of software-based hardware which doesn't replicate a specific hardware component.
-            I/O devices or simply virtio, are also made out of computer
-            code. Contrary to emulated hardware, they function as a
-            generic piece of software-based hardware which doesn't
-            replicate a specific hardware component.
 
 ### Paravirtualization
 
-Paravirtualization refers to the emulation practice of letting an
+Paravirtualization refers to the emulation practice of letting an operating system running in a virtualized environment know that it is running in such an environment.
-operating system running in a virtualized environment know that it is
-running in such an environment.
 
-Under this configuration, more efficient communication methods are
+Under this configuration, more efficient communication methods are available between the host and the guest, including VirtIO devices (e.g.: virtio-net for network devices, virtio-blk for block storage devices). Such devices can communicate directly with the host, instead of emulating every single command of an IDE, SATA, SCSI or NVMe device, as it is the case for model-based emulation.
-available between the host and the guest, including VirtIO devices
-(e.g.: virtio-net for network devices, virtio-blk for block storage
-devices). Such devices can communicate directly with the host, instead
-of emulating every single command of an IDE, SATA, SCSI or NVMe device,
-as it is the case for model-based emulation.
 
 ### Virtual machine
 
-A virtual machine is a recreation of a real, physical, silicon-based
+A virtual machine is a recreation of a real, physical, silicon-based computer using software. It performs almost exactly as a physical computer, and can thus host an operating system.
-computer using software. It performs almost exactly as a physical
-computer, and can thus host an operating system.
 
-The expression "virtual machine" is often abbreviated VM. VMs are also
+The expression "virtual machine" is often abbreviated VM. VMs are also often referred to as guests, in contrast to the hosts that host them.
-often referred to as guests, in contrast to the hosts that host them.