Add the hardware introduction

book/src/02_hardware.md

@@ -0,0 +1,33 @@
+# The Game Boy Advance hardware
+
+The Game Boy Advance was released by Nintendo in Japan in March 2001 and in North America in the following June.
+It has a 2.9 inch screen with a 240x144 pixel resolution, and contains a 32-bit 16.8MHz ARM CPU.
+It was developed to be the successor to the Game Boy Color and internally codenamed the 'Advanced Game Boy' (agb) which is where this crate gets its name.
+
+# What makes the GBA unique?
+
+The Game Boy Advance is (fairly) unique amongst retro handheld consoles.
+It was developed at a time where processors weren't powerful enough to be able to push an entire screen of pixels to the screen every frame.
+Therefore, it has a special Pixel Processing Unit (PPU) which is sort of similar to a modern day graphics card, except it is very games focused.
+For example, the GBA has a concept of 'hardware sprites' and 'hardware backgrounds' which we'll go in to more detail in the next section.
+This hardware 2d capabilities gives the GBA the unique characteristics with the games developed for it.
+
+However, despite this, it is possible to write code for it using modern tools and programming languages thanks to the ARM CPU it contains.
+The CPU is modern enough to be supported by LLVM and rust to give a reasonably trouble free experience.
+
+So the GBA lets you take advantage of modern tooling while also giving you the ability to see what programming for retro consoles was like at the time!
+
+# Capabilities of the hardware
+
+The GBA is fundamentally a 2D system, and a lot of the hardware accelerated graphics is designed to support this.
+The relevant features for this book are:
+
+* 256 sprites which can be from 8x8 to 64x64 pixels in size
+* 4 background layers which are enabled / disabled depending on the graphics mode
+* Background tiles, 8x8 pixel tiles are used in the background layers if they are in tile mode.
+* 8-bit sound. You have the ability to send 8-bit raw audio data to the speakers (optionally stereo).
+
+You can read more about the GBA on [gbatek](https://rust-console.github.io/gbatek-gbaonly/).
+
+agb tries to abstract some of this away from you to give you less to remember and less that can go wrong.
+If you want to try playing around directly with the hardware, the best place to look is [tonc](https://www.coranac.com/tonc/text/).

book/src/SUMMARY.md

@@ -1,3 +1,4 @@
 # Summary
 
 - [Introduction](./01_introduction.md)
+- [The Game Boy Advance hardware](./02_hardware.md)