![]() Virtually all the PCs today have a BIOS option that allows to boot from the network. PXE: is a Pre-boot Execution Environment it is not technically an independent "protocol", it is an environment that uses protocols like DHCP and TFTP, created to allow a PC to retrieve its booting code from a network instead of a HDD. Wol: Wake-on-LAN (WoL) is an Ethernet computer networking standard that allows a computer to be turned on or awakened by a network message. Enough people have enjoyed dabbling with PXE that such information is probably relatively easy to find. Before dedicate yourself to a specific idea that relies on PXE to start up a specific operating system, take a moment to read about how easy it is to use that operating system with PXE. So, different operating systems may support the PXE experience with different degrees of ease. Other operating systems may be based on a design that might expect to see all of the critical data sitting on a physical disk. They may support being able to start up with a minimal amount of data, and then use the network to locate even more data. Note that some operating systems might work better with PXE than others. The operating system that PXE boots up will be whatever code is on the image that gets downloaded. PXE can download an operating system you can even have the server provide different boot images so that the computer can download a different operating system each time it boots. I presume that add-on cards can use PXE when the BIOS checks if any add-on cards have an "option ROM" (similar to how an add-on card which is a RAID controller can allow the user to enter a RAID management tool before any operating system is loaded from a disk). When I've typically seen the option to use PXE, that option was built into the BIOS. That would prevent an operating system from being active.) (Generally including fans, and I presume that the CPU and main system RAM might also be lacking power. WoL is generally OS-agnostic, because no operating system is running, because the much of the computer is powered off. They aren't really related to each other. They are both related to the overall gigantic process of a system starting, and both involve network cards, but the similarities basically end there. You could use WoL and then PXE, so both are used. So, using PXE does not imply that WoL was used to turn the system on. PXE can be used when the system boots up with WoL, or when the system turns on because someone pressed the power button to turn on the computer, or possibly because software told the computer to perform a "cold"-style (full) restart. Using WoL does not mean that PXE will be used. WoL "wakes" the computer up, and that's all WoL does. What does the computer do when it powers on? It boots. So, WoL and PXE don't have to be related at all. The BIOS might just boot straight to the hard drive. "Normally" might involve PXE, or it might not. With WoL, the computer then boots up normally. The entire PXE process may use some other protocols, like DHCP and TFTP. After downloading code from the PXE server, the PXE client will run that code. ![]() If the PXE client (which is commonly built into the circuitry/chips on the computer that is booting) can locate a PXE server, then the PXE client will download code from the PXE server. This process searches a network for code to boot. Instead of booting from code on the hard drive, or booting code from a CD, the PXE process can be what is used for booting up the computer. PXE (which I have heard pronounced as "PiXiE", by multiple people) is related to how the computer boots. To make all that happen, you need another computer on the network to send a magic Wake-on-LAN frame that will be recognized by the computer that supports WoL. Once the computer powers on, the computer will do what the computer always does whenever it powers on: the computer will boot. If that pattern was seen, then WoL would send a message to the system (perhaps to the intelligent ATX power supply, or the motherboard's WoL pins?) to have the system "wake up" more fully. If the network card was using Wake On LAN, then it would check incoming Ethernet frames for a particular pattern. It may seem like the computer is using no electricity because it is quiet because no fans are being used, but a tiny amount of electricity can be made available for some of the cards. These might have been made for providing some tiny amount of power or data communication. As I recall, older computers would sometimes use a separate (set of) wire(s) that connected to the network card. Computers that are "powered off" might actually use up a little bit of electricity, and be able to perform some very minor functions. ![]() Wake On LAN (WoL) is a feature that allows a computer to be powered on.
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