A netboot is the process of booting an operating system over a network. The operating system image is stored on a central server's hard drive (in this case the Core), and loaded into the RAM of the PC which is requesting the netboot.
In many ways, it is similar to booting from a LiveCD or floppy, but the storage media is on the network.
Hardware enabled netboot
Many newer PCs have PXE built into the BIOS and are able to netboot. Older PCs from the 1990s may not have this capability.
Many current Ethernet NIC cards have a hardware chip (PXE-ROM) that allows booting over a network. This option is selected from the BIOS configuration on the PC.
Netbooting is more difficult wirelessly if the wireless card does not have an embedded PXE-ROM chip. Check the manufacturer's specifications. Some users have used wireless bridges to enable wireless netboots.
It the PC has both an active wireless and a wired Ethernet card, or multiple active wired NIC cards, it can be tricky to set which card to use for PXE netboot.
In general, direct netbooting from the BIOS is more successful over a single wired connection.
Software enabled netboot
Alternatively, a netboot can be specified using a boot loader on the local PC's hard drive, such as GRUB. See this discussion.
This can be configured to use different Ethernet cards and allows for greater flexibility, but there is a certain amount of configuration and Linux knowledge required.
Netbooting in LinuxMCE
LinuxMCE can automatically configure itself to allow the Media Directors to do a "Network Boot". In the past, network booting has been used mostly by Apple computers, and Windows generally hasn't supported it. Nevertheless, nearly all modern computer are capable of doing a network boot, offering some significant advantages.
When a computer does a network boot it means that it does not use its internal hard drive at all. Instead it boots up off the Core. This allows you to leave your current computer system on your local hard drive untouched by LinuxMCE, and you just hit a button on the remote to indicate if you want to use your computer like a normal PC (normal boot) or as a media director appliance (network boot). When it boots up as a Media Director, you don't have any computing issues to worry about. It functions just like an appliance -- no start menu, no software to install, nothing to configure, no viruses to worry about. This solves one of people's biggest complaints with media PC's (like Windows XP Media Centers) -- when they just want to watch TV, listen to music, or play a DVD they don't want to mess with a computer. They just want an appliance. With network boot you get the best of both worlds--it's a computer when you want to do computing, and an appliance the rest of the time.
Best of all there's no software you need to install to make it work. When you first turn your computer on, just press the key to enter the BIOS or setup program. There is normally an option to enable network boot, sometimes called "PXE". (This is an embedded Linux netboot protocol.) There will also be an option for boot order. Put the network boot option before the hard drive boot option -- that way the Core can tell the computer whether it should do a network boot or boot like normal.
If you can't figure out how to set this in your computer, you should contact the manufacturer's tech support. You can also try LinuxMCE's support and forums.
Normally, once you enable network boot in your BIOS, every time you turn on your computer it will show you this MAC Address for a few seconds. There is also an Advanced / IPs and Mac's page in the LinuxMCE Admin site that will show all the Mac Addresses in use in your home.
DHCP must be enabled on the Core to use netboot. You can do this by checking the box in the installation wizard, or after the fact from the LinuxMCE Admin web site.
Disadvantages of netbooting
Netbooting can be slower than booting from the hard drive -- depending on network speeds, it can be much slower.
In addition, if there is limited memory on the client, swap time is potentially slower over the network. The hard drive used by the peripheral PC remains on the central Core, so in effect, the effective "bus speed" becomes the data transmission speed of your network.
Lastly, unique hardware drivers and configurations for the client may not be recognized by a netboot, potentially causing a kernel panic (i.e. the hardware can't be recognized well enough to netboot the OS).
Alternatives to netbooting
This may seem like a silly section, but the creators of Pluto and LinuxMCE are enamored of the concept of netbooting. Personally, I don't like it, for the reasons listed above.
Very few PCs these days come with small hard drives, and it seems trivial to me to set up a second partition (using the Gparted Live CD, for example) on any PC that I intend to use as a Media Director. I simply install LinuxMCE on that second partition and configure it to automatically start as a Media Director. When I start the PC, the GRUB bootloader will give me the choice of using it as a Media Director or of using the native OS on the primary partition anyway. This is slightly less troublesome then using netboot (in which I have to change the BIOS settings), in fact.
Booting LinuxMCE from a second partition on the hard drive is far faster than performing a netboot. Furthermore, I can even disable the Kubuntu hardware auto-detection modules in order to speed up the boot process even more (but that's not a job for a newbie!)
Plug and play is great, but touch and go is better!
See also: Automatic diskless boot of media directors