add hardware description

Signed-off-by: Michel-FK <michel.stempin@funkey-project.com>

docs/developers/software/system/architecture.md

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+The **FunKey S** retro-gaming console software contains a set of
+console emulators, standalone games, applications and utilities using
+a custom Operating System (OS) that from now on will be referenced as
+**_FunKey-OS_**.
+
+The **FunKey-OS** is a Linux-based operating system, optimized for the
+**FunKey-S** hardware, with a special focus on performance and fast
+boot time.
+
+## Instant Action
+
+The **FunKey S** introduces a unique feature called **_Instant Action_**,
+which enables automatically saving the running state when closing
+the console before turning it off, and restoring this state when
+opening and turning it back on in a matter of seconds.
+
+This feature is only possible because of the optimized fast boot time
+detailed in the [Boot Process](bootprocess.md) section.
+
+## Storage
+
+The only storage system available in the **FunKey S** is its
+integrated MicroSD card. Most of its contents is made available to a
+host computer when connected over USB.
+
+The MicroSD card format is detailed in the [Disk
+Partition](partition.md) section.
+
+## Video Processing
+
+The **FunKey-S** CPU does not feature a GPU. For this reason, the
+**FunKey-S** cannot use a hardware-accelerated OpenGL engine, and
+adding a software-emulated OpenGL-ES engine is not efficient, given
+the limited CPU performance.
+
+However, because of the small screen size and the fact that all
+applications are used in full-screen mode only, there is no need for a
+full-blown windowing system like X11, which greatly simplifies the
+video processing as no window overlapping or frame decoration is thus
+required.
+
+Instead, all graphical computations are performed by the CPU itself,
+directly into the video frame buffer that will be sent to the screen
+for display.
+
+## User Input
+
+The **FunKey S** has no standard keyboard but features common
+console-oriented controls in the form of a D-Pad, A/B/X/Y Pad,
+Menu/On/Off, Fn and Start buttons.
+
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docs/developers/software/system/bootprocess.md

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docs/developers/software/system/init.md

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docs/developers/software/system/kernel.md

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docs/developers/software/system/partition.md

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docs/developers/software/system/recovery.md

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docs/developers/software/system/rootfs.md

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docs/developers/software/system/shared.md

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