Thanks Meter 54
Join Date: Sep 2010
Location: Sydney, Australia
Samsung stopped genuinely supporting this phone quite a while ago. The burden of updating the device has fallen onto the development community. Given that the I9000 is one of the most popular Android phones, LOTS of development has taken place since then.
The kernel on this device is part of the boot image, on its own partition. Recovery is coupled to that partition.
Rooting a device adds a new binary (su) to the system partition. This file is given permission to run as user 0 (root) and acts as a proxy for other processes to perform privileged actions (deleting system files, mounting partitions, accessing all data, etc).
Most custom ROMs come pre rooted since rooting is quite popular. Titanium Backup is the exemplar for what an application can use root privilege for.
Installing a custom ROM does not require the stock ROM to be rooted, it requires a custom kernel (with a cwm or twrp based recovery).
Most high quality custom ROMs (read CyanogenMod) have scripts to protect the efs partition while flashing.
As long as you can get into download mode on your phone you can always get back to stock firmware. The service centre won't know the difference.
The bootloaders are provided by Samsung, these are not replaced by custom ROMs.
Personally I run a modified build of CM10 and use a radio from the Nexus S (KJ1). I'm very happy with the overall battery life of my phone, signal quality is good in Australia (can't say with certainty for any other part of the world) and performance is quite snappy.
Sent from my Nexus 7 using Tapatalk 2