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+---
+title: "23-IO-systems"
+aliases: 
+tags: 
+- cosc204
+- lecture
+---
+
+interactive between device drivers and IO devices
+
+# Hardware
+- IO device linked to machine via Port
+- link is a set of wires called a Bus
+- as each end of the link is a device controller (basically a process)
+- ![diagram|400](https://i.imgur.com/qnmTxrb.png)
+
+![more complete diagram of PCI bus|400](https://i.imgur.com/fbJqpwr.png)
+
+device controller registers
+- each contoller has registers for holding signals
+- CPU can read and write these
+- some hold data some control signals
+
+adressesing devices
+- each port has an address range
+- CPU can issue IO instructions to particular addresses
+- communication can be 1 byte at a time for via direct memory access
+
+# Kernel interface
+
+# Performance