> For the complete documentation index, see [llms.txt](https://book.bsdcn.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://book.bsdcn.org/4.3-bsd-unix-cao-zuo-xi-tong-she-ji-yu-shi-xian/di-yi-bu-fen-gai-lan/2.8.-she-bei.md).

# 2.8 设备

硬件设备可以分为有结构的和无结构的两类，分别称为块设备（block device）和字符设备（character device）。进程通常通过文件系统中的特殊文件访问设备。对这些文件的 I/O 操作由驻留在内核中的软件模块处理，称为设备驱动（device driver）。多数网络通信硬件设备只能通过进程间通信设施访问，在文件系统名字空间中没有特殊文件。这是因为裸套接字接口提供了比特殊文件更自然的接口。

有结构设备或块设备的典型是磁盘和磁带，包括大多数随机访问设备。内核对面向块的有结构设备支持“读-改-写”式缓冲操作，使它们可以像普通文件那样完全按随机字节寻址的方式读写。文件系统创建在块设备上。

无结构设备指不支持块结构的设备。常见的有通信线路、光栅绘图仪以及不带缓冲的磁带机和磁盘机。无结构设备通常支持大数据块的 I/O 传输。

无结构设备之所以称为字符设备（character device），是因为最早实现的一批是终端设备驱动。内核面向这些设备驱动的接口，后来证明对其他非块结构的设备同样方便。


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