Application I/O Interface

We can further divide devices into the following categories:

1. Block vs. Character devices.
   • This is about the size of data that the OS can access within the device at once.
   • Block devices can be accessed one block at a time. A block is a fixed size of data, usually standing at a multiple of 512 bytes. Block sizes of 4k (= 4096) and 8k (= 8192) bytes are common.
   • Examples of block devices include hard disk drives, solid-state drives, and USB flash drives.
   • Character devices can be accessed one byte at a time (remember that 1 byte can store exactly one character or a small integer between 0-255.)
   • Examples of character devices include the mouse, the keyboard, and the monitor.
   • As a general rule, every peripheral I/O device is a character device.