Preboot Execution Environment

The concept behind the PXE originated in the early days of protocols like BOOTP/DHCP/TFTP, and as of 2015[update] it forms part of the Unified Extensible Firmware Interface (UEFI) standard.

In modern data centers, PXE is the most frequent choice[1] for operating system booting, installation and deployment.

This goal requires a client to use a set of pre-boot services, based on industry standard network protocols.

In this case the availability and subjection to standards are a key factor required to guarantee the network boot process system interoperability.

BOOTP implementation difficulties, among other reasons, eventually led to the development of the Dynamic Host Configuration Protocol standard RFC 2131 (DHCP) published in 1997.

The pioneering TFTP/BOOTP/DHCP approach fell short, as at the time, it did not define the required standardized client side of the provisioning environment.

These protocols have been selected because they are easily implemented in the client's NIC firmware, resulting in standardized small-footprint PXE ROMs.

DHCP is used to provide the appropriate client network parameters and specifically the location (IP address) of the TFTP server hosting, ready for download, the initial bootstrap program (NBP) and complementary files.

NBPs are just the first link in the boot chain process and they generally request via TFTP a small set of complementary files in order to get running a minimalistic OS executive (i.e. WindowsPE, or a basic Linux kernel+initrd).

At this point, the remaining instructions required to boot or install a full OS are provided not over TFTP, but using a robust transfer protocol (such as HTTP, CIFS, or NFS).

Corporate DHCP servers are usually subject to strict policies that are designed to prevent easily adding the additional parameters and rules required to support a PXE environment.

The proxyDHCP approach has proved to be extremely useful in a wide range of PXE scenarios going from corporate to home environments.

Even when the original client PXE firmware has been written by Intel and always provided at no cost as a linkable IA32 object code format module included in their Product Development Kit (PDK), the open source world has produced over the years non-standard derivative projects like gPXE/iPXE offering their own ROMs.

has made PXE the fastest method available for installing an operating system on a client when competing against the classic CD, DVD, and USB flash drive alternatives.

Microsoft created a non-overlapping extension of the PXE environment with their Boot Information Negotiation Layer (BINL).