[HD2 Android Q&A, Help & Troubleshooting and Genera] zarathustrax:
I have to disagree with a lot of what the post above mine said... The main difference between NAND and SD builds is with NAND builds you can use clockwork recovery, remove and replace your SD card while booted in android, and maybe a few other small improvement in stability and performance, but nothing too noticeable. Speed and battery life are about the same. You might get a little better battery life on standby with NAND. I generally got 3-5ma drain on standby with NAND, while I get 4-6ma on standby with SD. Speed and performance are pretty much the same because when you're running something with either type of build, it does it from RAM with either type of build. When an app or a process is running, it goes into ram, regardless of where the info was stored. NAND and SD are just the 2 options of where the data is stored when it's not being used by ram. Actually, the NAND in the HD2 can be slower than the NAND in good quality SD cards... but the random access speed is good in the HD2 NAND. But with a high quality SD card, you can get just as good random access speed with SD. That is what makes the performance difference with different SD cards... when the OS is trying to access small amounts of data or write small amounts of data, different SD cards will take different amounts of time to access... and the class rating of the card has nothing to do with that... in fact, class 2 cards tend to have better random access times than class 6 or 10.

But anyways, if you have a good SD card, performance and battery life are about the same... depending on the build of course. Desire HD builds tend to run a little better on NAND... but some recent SD DesireHD builds are good, too. AOSP and CM builds run pretty much the same off of SD and NAND as far as I can tell.

RAM builds work by loading more of the OS files into RAM at startup so that the random access speed of them is improved greatly, since RAM is the fastest memory and where any data is loaded to run anyways... it cuts down on the need to access the SD card for as many small system files, which improves performance and battery life in theory. The RAM is used anyways, so it doesn't use any more power keeping extra data in RAM, and since the SD card isn't accessed as much, it saves power there. But SD doesn't use much power anyways, so it's not really a noticeable power reduction. Also, RAM builds are still pretty experimental, and can have problems with data corruption... if any changes made to the os are not recorded to the SD, then if you lose power suddenly, there can be problems. Also, keeping all those system files in RAM causes you tohave less RAM available to run other apps and such... thats why there's no RAM builds for DesireHD builds, because there's not enough RAM. Personally, I never noticed too much of an increase in RAM builds performance compared to other AOSP SD builds like JDMS. Also, I'm not sure why, but I don't think RAM builds worked very good with NAND. But in theory, the system files in RAM is a good idea, especially for SD cards so it takes some stress off the SD cards. When running a build off SD, your accessing the SD to read and write system files while also accessing it as normal to run your apps or play your music or other data you have on SD. Keeping system files in RAM cuts down on the work the SD needs to do in the same way installing android to NAND does... then the SD is just used to access your media files or apps or data.

So in the end, it all depends on what you want from your phone... if you are not going to use winmo or wp7, and only use android, you might as well put android on nand, even if the improvement isn't that noticeable, because you can then use clockwork for easy updating or flashing roms, and you can change out your sd card, and there may be other small improvements. But if you still use winmo or wp7, then you have to decide if it's worth losing the ability to run more than one OS to give your android the added functionality of clockwork and other improvements. I use android on NAND for a month or so, but I didn't like how it turned my phone into just another android phone... it couldn't do anything that you couldn't do with a desire or evo or other android phone. But with the ability to run winmo or wp7 also, it's the only phone that can do it this well. When wp7 was released for the HD2, it was perfect for me because I wanted to try that OS out, and now I love that OS almost as much as android... I would have a hard time picking between the 2... luckily I don't have to. No other phone can run both of those OS's, either... I feel like I'm really making use of my HD2. If I just wanted android, I would've bought a native android phone from the beginning. But the great thing about the HD2 is no matter what OS you want, the HD2 can do it. People who want just android can make their HD2s almost like a native android phone now that it has clockwork recovery support. People who want 2 OS's can do that too. Android runs great from both SD and NAND... so use what works for you.