The /dev directory belongs to the process manager and contains device files.

The files that this directory includes may include:

CD-ROM block devices; see devb-* in the Utilities Reference for driver information.
Text mode console TTY device; see devc-con in the Utilities Reference.
The device that's used for diagnostic log messages; on a full x86 system, this is a write-only device managed by the system logger, slogger. Buildfiles for embedded systems may configure a link from this path to another device, such as a serial port. See slogger in the Utilities Reference.
Floppy disk block devices; see devb-fdc in the Utilities Reference for driver details.
Hard disk block devices; data representing an entire drive, spanning all partitions; see devb-* in the Utilities Reference.
Hard disk partition block devices; the data in these devices is a subset of that represented by the corresponding hdn file; see devb-* in the Utilities Reference.
A directory owned and operated by io-pkt*, under which you can find files relating to the network devices for your various LANs. C programs can perform devctl() operations on these files to interact with the driver, e.g., to obtain driver statistics.
Note: Only legacy io-net drivers create entries under /dev/io-net/; native io-pkt* drivers don't.
A device that represents all physical memory.
/dev/mq, /dev/mqueue
A pathname space where entries for message queues appear; for more information, see mq and mqueue in the Utilities Reference.
A "bit bucket" that you can direct data to. The data is discarded.
Parallel ports e.g., for parallel printers; see stty for configuration, and devc-par for driver details in the Utilities Reference.
Adopted by the PCI server on the machine, this device lets programs communicate with the PCI server. See pci-* in the Utilities Reference.
Adopted by the pipe manager. The presence of this file tells other programs (such as a startup script built into an OS image) that the Pipe manager is successfully running.
The control side of a pseudo-terminal device pair. Pseudo-ttys are named with a letter (p–z or P–T) followed by a hexadecimal digit, making it possible to have up to 256 devices. See devc-pty in the Utilities Reference.
Read from this device to obtain random data; see random in the Utilities Reference.
A pathname space where entries for named semaphores appear.
Serial ports. See stty for configuration, and devc-ser* for driver details in the Utilities Reference.
Contains files representing shared memory regions on the system (also sometimes used for generic memory-mapped files). For more information, see the description of the RAM "filesystem" in Working with Filesystems.
A device managed by slogger, used to read or write system log messages. Try sloginfo /dev/slog. See slogger and sloginfo in the Utilities Reference for more information.
This directory is owned and managed through the TCP/IP stack, which is included in io-pkt*. This directory contains pathnames through which applications interact with the stack. For more information, see the TCP/IP Networking chapter in this guide.
This file is managed by procnto. Text written to this device is output through debug output routines encoded in the startup code for your system.

The actual result, therefore, varies from board to board. On a standard PC (using startup-BIOS), the default is to write to the PC console. For more information, see startup-* in the Utilities Reference.

A virtual device owned by the process manager (procnto) that resolves to the controlling terminal device associated with the session of any process that opens the file. This is useful for programs that may have closed their standard input, standard output, or standard error, and later wish to write to the terminal device.
The slave side of the corresponding /dev/pty[p-zP-T][0-9a-f] file. The program being controlled typically uses one of these files for its standard input, standard output, and standard error.
Supplies an endless stream of bytes having a value of zero.