I/O devices --- Chapter 12 in the book.

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Device drivers:

. the lowest layer in a kernel, provided by device manufactures;
. present a uniform interface about the device to the upper layers of the 
	kernel, and hide idiosyncronys about the device hardware implementation;

. For example, the file system code in the kernel talks to the disk's
	device driver to read and write disk blocks;

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Hardware associated with I/O devices:

. port;

. bus;

. controller;

. I/O registers: memory-mapped access to I/O registers;

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Polling versus Interrupts (section 12.2.1 and section 12.2.2);

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DMA (Direct Memory Access); section 12.2.3;

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Application I/O interface:

. device types;

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What a Kernel I/O subsystem must do:

. I/O scheduling;

. buffering: for speed-matching purposes, for caching purposes, for spooling
	purposes;

. caching;