Daaavviiddd wrote Hello, and welcome to JTAG 101! I started to write this as instructions for a customer of mine, but then decided everyone should know. If this really helped please hit thanks, it helps me out and costs you nothing.
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JTAG intro
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It's 2010, and the use of JTAGs has gone primarily to running modded Call of Duty: Modern Warfare 2 lobbies. Theres nothing wrong with this, Its modding at its best after all. But Im here to remind you that JTAGs originated long before MW2 even existed, and have so many more uses than online lobby modding. With a jtagged console, you have the power to run unsigned XEX files. XEX files are like .EXE files on your computer, but the Xbox is programmed not to run any of these files that do not have a valid digital signature by Microsoft. The JTAG modification allows modified XEX files to run, which can load more modded FF files that contain game settings and configurations.
With a JTAG console you have the power to do anything within the limits of the hardware only, you are no longer limited by the software. You can do all of the following on a JTAG:


-Run classic emulators
-Get free downloadable game from the Marketplace
-Run custom Dashboards and software
-Share mods with other people over Xbox LIVE
-Modify accounts and files on the Hard Drive
-AND MUCH MORE


Although almost everyone with a JTAG will run a MW2 lobby sometime, I encourage you to use it to its fullest extent. Xbox LIVE is overrun with 10th Prestigers, does there really need to be more? Dont be a N00B with you tagged box!
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Xellous
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Xell is a second stage bootloader for the Xbox that is loaded by a loader (I know that sounds weird but it came straight from the Wiki page, so dont comment on it.) It was an outcome of the Free60 Wiki project. Xell catches CPU threads, sets them up, loads an ELF file from either network (tftp) or CDROM (ISO9660), and launches it. It's made to boot Linux. Xell is accessed by powering on the Xbox with the DVD drive open (use the eject button). Xell can display information such as console CPU/DVD keys, and other important strings. Xell can also install updflash.bin files automatically. To do this simply place the file on the root of a USB flash drive, and Xell will install it automatically.
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XeX Menu
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XeX Menu is a program to browse files on the HDD and external devices, and run them. It is labeled by the Xbox as a Game Demo. If you are using your JTAG online and in XeX Menu, it will appear to others as Session Sample.
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Keyvault Intro
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A Keyvault is a file containing the keys of the console, if your JTAG gets banned from LIVE, it will be console banned, rendering a normal console useless. But since you have an almighty JTAG you can unban it! You purchase a KV file from a key vault seller, and put those keys in your console, so LIVE thinks it is a different console when its really the same modified hardware. Anytime you want to install new keys to the NAND, the file should be 16.5 MBs in size, and named updflash.bin
NO CAPS IN FILE NAMES EVER!!!
When you purchase a keyvault it will be named kv_dec.bin, and will be very small in size
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Installing Keyvaults
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To make a kv_dec.bin file into a updflash.bin file, you need to use 360 Flash Tool, there are many tutorials on the internet about how to do this. Its very confusing the first time but as long as you follow directions you will be fine, and even if you get Christmas Lights from a bad KV you can restore the console as long as you can boot into Xell. All you have to do is load your original modded kernel in Xell and it will install to NAND.
If your console gets RROD after trying to install a KV, the only way is to dump the NAND to your computer through an LPT cable.
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How to know if someone is trying to scam you
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If you have ever been playing online, and someone claims they have a JTAG (especially in MW2) here are some questions you can ask them:


-What type of motherboard do you have?
-What type of Keyvault do you use? (1 or 2)
-What version of Freeboot do you use?


If they cannot answer or hesitate to answer one or more of these then it is pretty clear they are lying. Also if they ask for Microsoft points or Xbox LIVE codes they are most likely lying. If they ask for headshots or another type of in-game trade, always demand to get the mods first, then you will help them.
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