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Can I install CM7 on 2.1 kernel?

Hi guys, another newbie question from me
Correct me if I'm wrong, but if I flash a v2.1 SBF, then the kernel will also be flashed to v2.1 as well right?
Ok, so we also have a variety of custom roms. Some are based on v2.2 kernel, while some are for v2.1.
Now my question is, I know that CM7 is based on v2.2 kernel. Currently, I'm using a stock v2.1 SBF, so the kernel is also v2.1 as well. I want to know that despite this, can I still flash CM7 custom rom (which again is based on v2.2 kernel) on my phone? Or can I only flash a CM6 custom rom that is based on v2.1 kernel?

chaoscreater said:
Hi guys, another newbie question from me
Correct me if I'm wrong, but if I flash a v2.1 SBF, then the kernel will also be flashed to v2.1 as well right?
Ok, so we also have a variety of custom roms. Some are based on v2.2 kernel, while some are for v2.1.
Now my question is, I know that CM7 is based on v2.2 kernel. Currently, I'm using a stock v2.1 SBF, so the kernel is also v2.1 as well. I want to know that despite this, can I still flash CM7 custom rom (which again is based on v2.2 kernel) on my phone? Or can I only flash a CM6 custom rom that is based on v2.1 kernel?
Click to expand...
Click to collapse
Are you rooted on stock 2.1? Even CM6 is on the 2.2.1 kernel, so you would have to flash the 2.2 Vulnerable Recovery and then reroot, if I'm not mistaken.
Sent from my Milestone using XDA Premium App

i think you can flash CM7 (if you editing rom)
XT720 use milestone's rom on 29 kernel

chaoscreater said:
Hi guys, another newbie question from me
Correct me if I'm wrong, but if I flash a v2.1 SBF, then the kernel will also be flashed to v2.1 as well right?
Ok, so we also have a variety of custom roms. Some are based on v2.2 kernel, while some are for v2.1.
Now my question is, I know that CM7 is based on v2.2 kernel. Currently, I'm using a stock v2.1 SBF, so the kernel is also v2.1 as well. I want to know that despite this, can I still flash CM7 custom rom (which again is based on v2.2 kernel) on my phone? Or can I only flash a CM6 custom rom that is based on v2.1 kernel?
Click to expand...
Click to collapse
your kernel will update after install the CM7, because CM7 contain the new 2.2 kernel, you can flash CM7 directly, but remember to flash the BPSW update.

skadude66 said:
Are you rooted on stock 2.1? Even CM6 is on the 2.2.1 kernel, so you would have to flash the 2.2 Vulnerable Recovery and then reroot, if I'm not mistaken.
Sent from my Milestone using XDA Premium App
Click to expand...
Click to collapse
Yes i'm rooted on stock 2.1. Initially, I couldn't get into OpenRecovery after flashing the stock 2.1 SBF, whereas I could when I was on stock 2.2. I did some searching and found this:
http://android.doshaska.net/rootable
and flashed the vulnerable recovery and now everything works fine. I got my phone rooted and currently using the TelusLite v5.2 for Eclair. However, i'm not sure if the vulnerable recovery is the 2.2 or not, i'm guessing it is?
Charles_l said:
your kernel will update after install the CM7, because CM7 contain the new 2.2 kernel, you can flash CM7 directly, but remember to flash the BPSW update.
Click to expand...
Click to collapse
Ok now i'm confused. From what I know, the bootloader for Motorola devices like the Milestone is locked. Therefore, we can't properly flash a custom rom on the phone, and we can't flash a different kernel either (which is why if you try to change one of the settings that relate to the kernel in OpenRecovery, you'll brick your phone).
So I've always thought that only flashing a stock SBF will change the kernel, and that the custom roms will rely on the stock kernel, hence why there're custom roms for different Android versions, like Eclair and Froyo? So ya i'm a little bit confused here.
Also, what's the BPSW update? What does it stand for and is that included in the CM7 custom rom topic? I couldn't find it and Google didn't find anything either.....

chaoscreater said:
Yes i'm rooted on stock 2.1. Initially, I couldn't get into OpenRecovery after flashing the stock 2.1 SBF, whereas I could when I was on stock 2.2. I did some searching and found this:
http://android.doshaska.net/rootable
and flashed the vulnerable recovery and now everything works fine. I got my phone rooted and currently using the TelusLite v5.2 for Eclair. However, i'm not sure if the vulnerable recovery is the 2.2 or not, i'm guessing it is?
Ok now i'm confused. From what I know, the bootloader for Motorola devices like the Milestone is locked. Therefore, we can't properly flash a custom rom on the phone, and we can't flash a different kernel either (which is why if you try to change one of the settings that relate to the kernel in OpenRecovery, you'll brick your phone).
So I've always thought that only flashing a stock SBF will change the kernel, and that the custom roms will rely on the stock kernel, hence why there're custom roms for different Android versions, like Eclair and Froyo? So ya i'm a little bit confused here.
Also, what's the BPSW update? What does it stand for and is that included in the CM7 custom rom topic? I couldn't find it and Google didn't find anything either.....
Oh and one more thing, I think this is a bug so can someone look into it? The statusbar hides itself and to unhide it, you have to ADWSettings (press the Menu capacitive button, in between the back and home button, and then click More, then choose ADWSettings).
Then, click on System preferences, and the first option is "Hide Statusbar".
The problem is, that option is by default already un-ticked, which means it does NOT hide your statusbar. And yet, the statusbar is hidden........the only way to fix this is to enable the option so that it actually hides it, then close everything and go back to your desktop, and then open ADWSettings again and then un-tick it. This will fix it and make the statusbar appear.
However, if you move your shortcuts/icons on the desktop around, or if you move it to the Trash, then this will undo the statusbar change and will make it hide again. So then you'll have to do this constantly, so I suggest you guys make sure your desktop shortcuts are fully configured, and then make the statusbar change at the end.
Click to expand...
Click to collapse
Yes, VR is based on 2.2.

sorry, what does VR stand for? And I still don't understand it, can you please explain?

chaoscreater said:
sorry, what does VR stand for? And I still don't understand it, can you please explain?
Click to expand...
Click to collapse
VR is vulnerable recovery, it's what is on android.doshaska.net/rootable

ahh I see......but I still don't understand the part about the kernel.
I thought that every new firmware version update will use a newer version of the kernel? If yes, then how can custom roms like CM7 that requires kernel for v2.2, be installed on stock v2.1? Unless both the v2.1 and v2.2 stock SBF use the same kernel version? But then again, why are there specific roms for Eclair and Froyo? If you look at this topic here:
http://forum.xda-developers.com/showthread.php?t=966812
the OP says that some of those roms might not work because of different kernels. So it leads me to believe that if you're on stock v2.1, then the kernel is different than if you're on stock v2.2, hence why the custom roms you can install are separated by Eclair and Froyo......
And lastly, if custom roms like CM7 will install the v2.2 kernel, shouldn't that require the bootloader to be unlocked?? I thought we can't change the kernel yet? I'm confused....

chaoscreater said:
ahh I see......but I still don't understand the part about the kernel.
I thought that every new firmware version update will use a newer version of the kernel? If yes, then how can custom roms like CM7 that requires kernel for v2.2, be installed on stock v2.1? Unless both the v2.1 and v2.2 stock SBF use the same kernel version? But then again, why are there specific roms for Eclair and Froyo? If you look at this topic here:
http://forum.xda-developers.com/showthread.php?t=966812
the OP says that some of those roms might not work because of different kernels. So it leads me to believe that if you're on stock v2.1, then the kernel is different than if you're on stock v2.2, hence why the custom roms you can install are separated by Eclair and Froyo......
And lastly, if custom roms like CM7 will install the v2.2 kernel, shouldn't that require the bootloader to be unlocked?? I thought we can't change the kernel yet? I'm confused....
Click to expand...
Click to collapse
What you're confusing is that the version of android such as 2.2 is NOT the Kernel. The only way for you to change the kernel per se is to flash an sbf such as the Eclair or Froyo sbf. These are signed by Motorola and have holes in the code that have been exploited so we can flash Custom ROMs. The only things that we can do is flash a custom ROM or flash an SBF through RSD Lite. Kernels cannot be changed otherwise.
Sent from my Milestone using XDA Premium App

ya I understand that, and that's exactly the reason why i'm confused.....
If you flash a v2.1 SBF, then your Android version is v2.1 (Eclair).
If you flash a v2.2 SBF, then your Android version is v2.2 (Froyo).
Now, the problem is that custom roms like CM7 requires the kernel for Froyo. In other words, you have to flash a stock v2.2 SBF first, so that your phone will be running Froyo and that the kernel will obviously be for Froyo as well.
So what I don't understand is, I'm using Eclair right now because I flashed a New Zealand v2.1 SBF. The Android version I'm running on is Eclair, and the kernel version should be for Eclair as well.
Then why is it that you guys said I can still flash CM7, which requires the kernel for Froyo?

chaoscreater said:
ya I understand that, and that's exactly the reason why i'm confused.....
If you flash a v2.1 SBF, then your Android version is v2.1 (Eclair).
If you flash a v2.2 SBF, then your Android version is v2.2 (Froyo).
Now, the problem is that custom roms like CM7 requires the kernel for Froyo. In other words, you have to flash a stock v2.2 SBF first, so that your phone will be running Froyo and that the kernel will obviously be for Froyo as well.
So what I don't understand is, I'm using Eclair right now because I flashed a New Zealand v2.1 SBF. The Android version I'm running on is Eclair, and the kernel version should be for Eclair as well.
Then why is it that you guys said I can still flash CM7, which requires the kernel for Froyo?
Click to expand...
Click to collapse
I have never tried flashing CM7 from Eclair, so I can't tell you that it will work. I upgraded to stock Froyo on Telus the day it came out and got frustrated with it and rooted the same day.
Sent from my Milestone using XDA Premium App

Hmm well I'd flash to stock Froyo as well, then I wouldn't have a problem installing CM7 because I know it'll definitely work. Except that the kernel for Froyo doesn't work well on my Milestone. Many people have problems with the Froyo kernel, mostly to do with connection problems like wifi or 3g.
I've had problem with my wifi where it connects to my router, but isn't sending/receiving any data. Either that, or it works for 5 mins and then disconnects itself afterwards.
Many people suggested to flash back to stock Eclair, so I did and my wifi works awesome right now and never had a connection problem yet. Currently, i'm using the TelusLite v5.2 custom rom for Eclair, and it works great but I wanna try out custom roms for Cyanogen Mod, like CM6 or CM7.
From what I know, CM6 is for Eclair because it uses the Eclair kernel. Whereas CM7 is for Froyo as it uses the Froyo kernel. However, I think the latest version of CM6 also uses the Froyo kernel, as somebody mentioned it in the CM7 topic somewhere.......so ya I'm pretty sure you CAN'T install CM7 on Eclair since the kernel requirement is different.
And yet, i'm confused with the answer in the 4th post:
http://forum.xda-developers.com/showpost.php?p=16834339&postcount=4

chaoscreater said:
Hmm well I'd flash to stock Froyo as well, then I wouldn't have a problem installing CM7 because I know it'll definitely work. Except that the kernel for Froyo doesn't work well on my Milestone. Many people have problems with the Froyo kernel, mostly to do with connection problems like wifi or 3g.
I've had problem with my wifi where it connects to my router, but isn't sending/receiving any data. Either that, or it works for 5 mins and then disconnects itself afterwards.
Many people suggested to flash back to stock Eclair, so I did and my wifi works awesome right now and never had a connection problem yet. Currently, i'm using the TelusLite v5.2 custom rom for Eclair, and it works great but I wanna try out custom roms for Cyanogen Mod, like CM6 or CM7.
From what I know, CM6 is for Eclair because it uses the Eclair kernel. Whereas CM7 is for Froyo as it uses the Froyo kernel. However, I think the latest version of CM6 also uses the Froyo kernel, as somebody mentioned it in the CM7 topic somewhere.......so ya I'm pretty sure you CAN'T install CM7 on Eclair since the kernel requirement is different.
And yet, i'm confused with the answer in the 4th post:
http://forum.xda-developers.com/showpost.php?p=16834339&postcount=4
Click to expand...
Click to collapse
I haven't heard of Eclair to CM7 directly. Every ROM except for the Eclair roms like you are running now are ALL based on Froyo. GB is based on the Froyo kernel, but is a gingerbread port.
Sent from my Milestone using XDA Premium App

yup I know. After all, there is no official Gingerbread support for Milestone (yet), that's why we don't have a v2.3 SBF to flash (therefore not able to get the kernel for Gingerbread).
But ya i'm pretty sure I got this sorted, after all the OP did specifically say that some roms might not work due to different kernels, which is mentioned in this topic here:
http://forum.xda-developers.com/showthread.php?t=966812
so ya you either have to flash the stock v2.1 SBF or v2.2 SBF in order to install specific custom roms that you want, depending on what kernel they're based on, right?
Oh well, guess i'll just stay with TelusLite v5.2 for now. It's pretty fast and stable so I guess that's good enough.

chaoscreater said:
yup I know. After all, there is no official Gingerbread support for Milestone (yet), that's why we don't have a v2.3 SBF to flash (therefore not able to get the kernel for Gingerbread).
But ya i'm pretty sure I got this sorted, after all the OP did specifically say that some roms might not work due to different kernels, which is mentioned in this topic here:
http://forum.xda-developers.com/showthread.php?t=966812
so ya you either have to flash the stock v2.1 SBF or v2.2 SBF in order to install specific custom roms that you want, depending on what kernel they're based on, right?
Oh well, guess i'll just stay with TelusLite v5.2 for now. It's pretty fast and stable so I guess that's good enough.
Click to expand...
Click to collapse
The issue is that TelusLite is no longer updated. Any issues that you will encounter may not be fixed. I've always found RSD Lite to be finicky, but you can always flash the 2.2 VR and try other ROMs and if you aren't happy, you can reflash the 2.1 and go back to TelusLite.
Many options for you to try out!
Sent from my Milestone using XDA Premium App

ya it seems like it. But the latest build (v5.2) was updated on July 2011 so it's only a month old? So ya not too bad. I haven't had any issues with it, and all the stuff that I use my phone for works fine on this rom so i'm pretty happy with it.
I only wanted to try out CM7 because it looks nice and that many of my friends recommended me to use it. But ur right, there're still other great roms out there that I can test out.
RSD Lite works well for me, never had a problem with it so i'm pretty happy. At least the flashing and rooting process on Android is fairly easy. Whereas on Windows Mobile or on Maemo (when I still had my Nokia N900), it was a pain in the ass, especially that the flasher program for Maemo doesn't work on Windows 7
Anyway, thanks A LOT for your help. You've helped me in the other topic I posted as well, I really appreciate you taking the time to answer my newbie questions

chaoscreater said:
ya it seems like it. But the latest build (v5.2) was updated on July 2011 so it's only a month old? So ya not too bad. I haven't had any issues with it, and all the stuff that I use my phone for works fine on this rom so i'm pretty happy with it.
I only wanted to try out CM7 because it looks nice and that many of my friends recommended me to use it. But ur right, there're still other great roms out there that I can test out.
RSD Lite works well for me, never had a problem with it so i'm pretty happy. At least the flashing and rooting process on Android is fairly easy. Whereas on Windows Mobile or on Maemo (when I still had my Nokia N900), it was a pain in the ass, especially that the flasher program for Maemo doesn't work on Windows 7
Anyway, thanks A LOT for your help. You've helped me in the other topic I posted as well, I really appreciate you taking the time to answer my newbie questions
Click to expand...
Click to collapse
Anytime! Let me know if you need anything else
Sent from my Milestone using XDA Premium App

chaoscreater said:
Hmm well I'd flash to stock Froyo as well, then I wouldn't have a problem installing CM7 because I know it'll definitely work. Except that the kernel for Froyo doesn't work well on my Milestone. Many people have problems with the Froyo kernel, mostly to do with connection problems like wifi or 3g.
I've had problem with my wifi where it connects to my router, but isn't sending/receiving any data. Either that, or it works for 5 mins and then disconnects itself afterwards.
Many people suggested to flash back to stock Eclair, so I did and my wifi works awesome right now and never had a connection problem yet. Currently, i'm using the TelusLite v5.2 custom rom for Eclair, and it works great but I wanna try out custom roms for Cyanogen Mod, like CM6 or CM7.
From what I know, CM6 is for Eclair because it uses the Eclair kernel. Whereas CM7 is for Froyo as it uses the Froyo kernel. However, I think the latest version of CM6 also uses the Froyo kernel, as somebody mentioned it in the CM7 topic somewhere.......so ya I'm pretty sure you CAN'T install CM7 on Eclair since the kernel requirement is different.
And yet, i'm confused with the answer in the 4th post:
http://forum.xda-developers.com/showpost.php?p=16834339&postcount=4
Click to expand...
Click to collapse
Well, you can open a CM7 zip package, you should see a file named "boot.img", that is the kernel, came from the stock Froyo SBF, so that it can pass the bootlooder checking, and it will replace the old kernel during the CM7 installation. That is why the kernel will update to the stock 2.2 kernel after you installed the CM7.

Charles_l said:
Well, you can open a CM7 zip package, you should see a file named "boot.img", that is the kernel, came from the stock Froyo SBF, so that it can pass the bootlooder checking, and it will replace the old kernel during the CM7 installation. That is why the kernel will update to the stock 2.2 kernel after you installed the CM7.
Click to expand...
Click to collapse
I see......in that case, can I replace the boot.img with the one for Eclair? I.e, use the 2.1 kernel instead of 2.2? I'm pretty sure this isn't possible since the custom rom is made to work with that particular kernel version, but maybe it does work?

[Q]a cm7 problem

i'm now using the cm7 built by temasek.
A serious problem is that my pc can‘t read my o2x phone when i use that rom.
however,,if i replace the stock kernel with an etana one or use other rom like cm9 or v20q,everthing works well......
and the miui also has the same problem...
i'd like to use a stock rom and i also want to have it read by my pc..
how should i do with this problem?is there anyone having the same problem?

Why would you want to use stock ROM?
I have done benchmark before and after flashing vadonka's kernel and specially I/O write speed improves drastically. You have non-OC'ed versions, so I don't really understand what you have got to lose.

LarsPT said:
Why would you want to use stock ROM?I have done benchmark before and after flashing vadonka's kernel and specially I/O write speed improves drastically. You have non-OC'ed versions, so I don't really understand what you have got to lose.
Click to expand...
Click to collapse
Maybe vadonka's kernel is great. ..but i do think the launcherpro works better on the stock kernel than on the etana. ...also the boot time increases after flashing the etana

If what you are trying to do is to push files to your phone from your pc, then try following the tip from XDA-TV. It worked well for me.
http://youtu.be/UI70UYug_zQ
Sent from my LG-SU660 using xda premium

[Q]Kernel ?

Hi, I would like to know what is kernel, and what would it change in the phone, performance and display, i'm a gamer, so i would like a good kernel for games like asphalt 6, FL Commando and And NOVA 6, and how to install it, i'm using Zeus 6.32n
thanks a lot
Sent from my LG-P970 using xda premium. If I Helped You, Hit The Thanks Boutton. Jesus !!

I must admit that p970 is not so hard developed yet and as far as im concerned, we havent got any custom kernel for stock-based rom like Zeus. However, Diana kernel (which is used in newest version of Zeus v.36) is best for performance and battery life. As long as someone wont make a miracle, its only-one custom kernel for stock based ROMs.
In addition, it has overclocking and is tweaked for performance, so why do you need other kernel? Try installing newest version of zeus ROM and test if you are pleased with results.

Similar question: So if i install the newest zeus i already have a new kernel on the phone or do i still need to update the kernel? I now have Zeus v7.03 and the kernel version: 2.6.35. Any help is appreciated! Thx
Hbohd said:
I must admit that p970 is not so hard developed yet and as far as im concerned, we havent got any custom kernel for stock-based rom like Zeus. However, Diana kernel (which is used in newest version of Zeus v.36) is best for performance and battery life. As long as someone wont make a miracle, its only-one custom kernel for stock based ROMs.
In addition, it has overclocking and is tweaked for performance, so why do you need other kernel? Try installing newest version of zeus ROM and test if you are pleased with results.
Click to expand...
Click to collapse

rooney_10 said:
Similar question: So if i install the newest zeus i already have a new kernel on the phone or do i still need to update the kernel? I now have Zeus v7.03 and the kernel version: 2.6.35. Any help is appreciated! Thx
Click to expand...
Click to collapse
If you install a newer Zeus Version 6.33 and up you have a different kernel that can use lower and higher frequencies. 2.6.35 is the basic linux kernel, alle Diana kernels have that number too. Up too diana kernel 2.3 it seems to be very stable, after 2.3 the kernels are all betas up till now and well beta is still experimental, for some it works well, for others maybe not. If you install Zeus 7.02 or .03 it comes with a beta kernel, but I'm rather sure you can still install the stable Diana kernel 2.3 after you installed Zeus 7.02 or .03.
BTW all that can be read in http://forum.xda-developers.com/showthread.php?t=1454274 , but OK it might take some time to go read that all, but before you ask more questions maybe you should at least try to read some of that thread (first page and maybe about last 3 weeks).

SaschaKH said:
If you install a newer Zeus Version 6.33 and up you have a different kernel that can use lower and higher frequencies. 2.6.35 is the basic linux kernel, alle Diana kernels have that number too. Up too diana kernel 2.3 it seems to be very stable, after 2.3 the kernels are all betas up till now and well beta is still experimental, for some it works well, for others maybe not. If you install Zeus 7.02 or .03 it comes with a beta kernel, but I'm rather sure you can still install the stable Diana kernel 2.3 after you installed Zeus 7.02 or .03.
BTW all that can be read in http://forum.xda-developers.com/showthread.php?t=1454274 , but OK it might take some time to go read that all, but before you ask more questions maybe you should at least try to read some of that thread (first page and maybe about last 3 weeks).
Click to expand...
Click to collapse
Thx for the information! I did read some of the thread, but as you said it will take some time to read the whole thing

Best choice Samsung Galaxy S I9000 CM 10.1 + Kernel + Modem

Hi everyone!
I installed last nightly build of CM 10.1 (31/03/2013) on my Samsung Galaxy S I9000.
I also use the standard kernel that comes with CM distribution and Semaphore's ClockworkMod Recovery 2.7.4
Everything is working great, my old phone is reborn! Except for the excessive battery drain...
I read that to solve that problem one possibility is to flash a different kernel (such as Semaphore's one or Devil's one) and to change the modem. Anyway answers on the web are neither organic nor clear.
According to you:
- which is the best kernel to use in order to solve the battery drain problem? (please give me the exact version)
- which modem should i install? and where do i find it?
- [noob question] if I flash a different kernel and then i upgrade to a new nightly build do I have to flash the different kernel again? I mean, if I upgrade to a new CM release my kernel is replaced?
Thanks a lot for your precious tips!

currently I'm using this http://forum.xda-developers.com/showthread.php?t=2024269 with the updated 4.2 devil kernel, quite fast, not having much luck with the modem though as the supplied one didn't seem to work, flashed a few from this thread http://forum.xda-developers.com/showthread.php?p=30588173&highlight=nz#post30588173 and finally got signal, but I'm unsure if these were meant to work with cm10.1 or not as it was an older thread for cm7/9 etc.. and I can't seem to find any info on cm10.1 modems specific to NZ
as for your kernel question; it kinda depends on the ROM, if it's an update then you will keep the kernel you had earlier, but new ROMs usually come with their own, I like to try out a few different ones and decide for myself what works for me, just make sure your kernel is made for the android version of your ROM, eg: there are devil kernels for 4.1.2 that will not work on 4.2.2, you need the 4.2 specific, also applies when flashing gapps..

Mackay and Infamous are really great and smooth. The built in kernel is very good. Set deep idle on but there is not much difference between cm10.1 kernel.

ROM & Kernels ?

I am newbie so please forgive me, Can some one please explain to me what a kernel is and why it matter?
Also say for example I install Werewolf CM10.1 ROM does the kernel also change to WerewolfJB automatically?
Sent from my LG-P880 CarbonRom

Yes because CM Roms run on different kernels and cant be used on stock or stock based kernels. And wise versa. And Kernels are...well not sure how to explain it. Let me try it. Is basically like a transmission. So better the transmission is so better runs and shifts the car. That's basically on a phone the same. Yes the processor is important but the kernel is what makes everything run like it should. I installed a costum kernel because the original one was so bad in battery life and this costum kernel is much better optimized. No more 10 or more % battery drain in standby in an hour. Battery life was pretty terrible on this phone now it is like a fully new phone with ok battery life.
Sent from my LG-P880 using Tapatalk 4

dimension3000 said:
I am newbie so please forgive me, Can some one please explain to me what a kernel is and why it matter?
Also say for example I install Werewolf CM10.1 ROM does the kernel also change to WerewolfJB automatically?
Sent from my LG-P880 CarbonRom
Click to expand...
Click to collapse
The kernel is the core-engine all other software runs on. To make an analogy with a car:
The chassis of the car is the phone, the engine is the kernel and the body is the ROM. This is not a very accurate analogy, but I hope you get the point.
Different kernels focus on different keypoints. Some are very battery-friendly, some favor performance, some offer extra functionality to the system, etc..So there is not a one-size-fits-all perfect kernel.
ROM's are usually based on a certain structure, which the kernel has to support. So for a stock ROM you need a different kernel then for a CM ROM. Most ROM come complete with a kernel, a few don't. So if you flash a ROM which contains it's own kernel you overwrite the kernel that is on your phone. So let's say you've got the Optimus Prime kernel and then install the latest CM build, you overwrite your OP kernel and have to re-flash it after installing the ROM to get it back.In your case the Werewolf CM10.1 ROM comes complete with the Werewolf kernel.
Hope this answers your questions.