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In computing, the Preboot eXecution Environment (PXE, sometimes pronounced as ''pixie'') specification describes a standardized client-server environment that boots a software assembly, retrieved from a network, on PXE-enabled clients. On the client side it requires only a PXE-capable network interface controller (NIC), and uses a small set of industry-standard network protocols such as DHCP and TFTP. The concept behind the PXE originated in the early days of protocols like BOOTP/DHCP/TFTP, and it forms part of the Unified Extensible Firmware Interface (UEFI) standard. Given fast and reliable local area networks (LANs), PXE is the most frequent choice for operating system booting, installation and deployment. == Overview == Since the beginning of computer networks, there has been a persistent need for client systems that are able to boot appropriate software images, using appropriate configuration parameters, both retrieved at boot time from one or more network servers. This goal requires a client using a set of pre-boot services, based on industry standard network protocols. Additionally, the initially downloaded and run Network Bootstrap Program (NBP) must be built relying on a client (the device to be bootstrapped via PXE) firmware layer providing a hardware independent standardized way to interact with the surrounding network booting environment. In this case the availability and subjection to standards are a key factor required to guarantee the network boot process system interoperability. One of the first attempts in this regard was the Bootstrap Loading using TFTP standard RFC 906, published in 1984, which established the 1981 published Trivial File Transfer Protocol (TFTP) standard RFC 783 to be used as the standard file transfer protocol for bootstrap loading. It was followed shortly after by the Bootstrap Protocol standard RFC 951 (BOOTP), published in 1985, which allowed a disk-less client machine to discover its own IP address, the address of a TFTP server, and the name of an NBP to be loaded into memory and executed. Difficulties on BOOTP implementation among other reasons eventually led to the development of the Dynamic Host Configuration Protocol standard RFC 2131 (DHCP) published in 1997. This pioneer TFTP/BOOTP/DHCP approach fell short because at the time it was not defined the required standardized client side of the provisioning environment. The Preboot Execution Environment (PXE) was introduced as part of the Wired for Management framework by Intel and is described in the specification published by Intel and SystemSoft. PXE version 2.0 was released in December 1998, and the update 2.1 was made public in September 1999. The PXE environment makes use of several standard client-server protocols like DHCP and TFTP (now defined by the 1992 published RFC 1350). Within the PXE schema the client side of the provisioning equation is now an integral part of the PXE standard and it is implemented either as a Network Interface Card (NIC) BIOS extension or today in modern devices as UEFI code. This distinctive firmware layer makes available at the client the functions of a basic Universal Network Driver Interface (UNDI), a minimalistic UDP/IP stack, a Preboot (DHCP) client module and a TFTP client module, together forming the PXE application programming interfaces (APIs) used by the NBP when needing to interact with the services offered by the server counterpart of the PXE environment. TFTP's low throughput, especially when used over high-latency links, has been initially mitigated by the TFTP Blocksize Option RFC 2348 published in May 1998, and later by the TFTP Windowsize Option RFC 7440 published in January 2015. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Preboot Execution Environment」の詳細全文を読む スポンサード リンク
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