Add I/O

I%2FO.md

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+## IO? Many many questions.
+
+- How shall the processor talk to external IO devices?
+- What types of devices shall be connected?
+- Where do we implement DMA, does each IO bus get its own mini microprocessor?
+  (We should look for a book specifically on I/O and how microprocessors typically handle it.)
+- How do we solve problems with Virtual Memory and Cache Coherence? *See*~[Patterson, 2009](#) for some suggestions.
+
+### Types of devices to be connected
+Note that for each item we will have to work out what the simplest standard method of connection is, whether we can use pre-written libraries or ICs to handle communications etc.
+
+- Serial
+- Keyboard
+- RAM
+- ROM (for firmware etc.)
+- Screens/Framebuffers (complex)
+- Hard Drives