some minor updates

phyllomeos/purpose.md

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 dateCreated: 2021-11-12T15:31:30.659Z
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-# Header
-Your content here
+## []{#anchor-31}Purpose
+
+Why would one prefers to use an operating system installed on virtual
+hardware ?
+
+Adding a layer of abstraction between the operating system and the
+virtualization-friendly hardware allows for support of newer operating
+systems, beyond what the physical hardware can support.
+
+-   By using Phyllome OS on Apple hardware that do not support the
+    latest iteration of macOS, one could create a virtual machine and
+    install the latest iteration of macOS anyway, further extending the
+    life of hardware.
+
+    -   **Note:** Phyllome OS does not and will **not** support running
+        macOS on anything but Apple hardware, as it is -- sadly -- not
+        allowed by Apple.
+
+-   Windows 11 requires a Trusted Platform Module (TPM). By using a
+    virtual machine alongside a virtual TPM on unsupported hardware, one
+    could still run Windows 11. The passthrough of a real TPM may also
+    be supported.
+
+### []{#anchor-32}Advantages
+
+More generally, a software-based/backed computer, or simply a virtual
+machine, has many advantages over a silicon-based computer :
+
+-   **Cost** : the cost of creating a virtual machine tends to zero
+-   **Flexibility** : a software-backed computer, alongside its
+    operating system, can be migrated to new physical hosts. In other
+    words, when a user acquires a new physical computer, the entire
+    computing environment may be copy/pasted to the new machine.
+-   **Compatibility** : contrary to silicon-based computers, which tend
+    to be optimized to work at most with only a handful operating
+    systems, a virtual machine can be designed to work with most
+    operating systems.
+
+### []{#anchor-33}Limitations
+
+Alas, it also comes with limitations, including but not limited to :
+
+-   Limited out-of-the box hardware support : hardware-assisted
+    virtualization is available on many computers but rarely activated
+    by default and not always correctly implemented. Users remain a the
+    mercy of good platform firmware and may have to explicitly activate
+    hardware-assisted virtualization in the BIOS/UEFI. Hardware
+    components are often not correctly isolated in IOMMU groups.
+
+    -   Offering first-class support for only a handful of curated
+        computers might provide an answer, at the price of
+        compatibility.
+    -   When it comes to IOMMU groups, a workaround[^30] might have to
+        be used for models that do not offer well-isolated IOMMU groups,
+        a workaround that has security implications.
+
+-   **Reliance on devices or controllers passthrough to cover edge cases
+    **: virtual hardware do not cover all features a user may expect to
+    have, including out of the box support for Bluetooth, wireless, or
+    sound adapters. For those cases, USB or PCI Passthrough might be
+    used.
+
+    -   Again, offering first-class support for only a handful of
+        curated computers might provide an answer, at the price of
+        compatibility.
+    -   New virtual hardware are expected, including paravirtualized
+        sound cards, which will improve the situation.