Android adb sideload command

Question

I am reading a tutorial on the sideload command at link.

It contains the steps of rebooting into recovery mode and using adb sideload [file].zip.

My question is that what does sideload actually do with that zip file ? In the past I have compiled AOSP and flashed a device using

• adb reboot-bootloader
• adb fastboot flashall -w

Is sideload trying to achieve something similar to the above ?

Edit:

I think my confusion relating to sideload stems from my lack of understanding of how Android's memory is structured. I found two links.

First is a link that explains Android partitions : partitions

Second is a SO answer, that explains Android's memory: memory

Now my understanding so far is this :

Android has RAM and ROM. ROM is divided into several partitions, namely, /system, /data, /boot, /recovery, /cache, /misc and /sdcard.

Now the link relating to sideload states that this command installs a zip file.

What I don't understand still is that, is this zip file, going to replace the entire ROM in Android ? Namely, will it have to have the right partitions as in the list above ?

This also makes me confused about a similar command 'fastboot flashall'. I know when I run it, the terminal goes by saying its writing to several of the partitions. So my questions boil down to these :

1) Is sideload replacing entire ROM ?

2) Is the related command 'fastboot flashall' also replacing entire ROM ?

3) Are there ways to replace select partitions ?

Thanks.

Answer 1

1. Yes and no. adb reboot-bootloader is used to get yoi into fastboot mode ard sideload is used to apply updates to a system which can be (and is oftenly) used to overwrite a stock OS. I used sideload for exactly that, my fairphone also delivers a small utility to factory reset every partioin of it using adb and sideload (this is the Windows version from scroll down here). Consider chris stratton's comment. You can look into adb backup and adb restore to only deal with user data and apps. Click me tenderly, click me hard. Pay attention as to apps can opt out of this - explanation in this brilliant answer by Izzy.

2. Depends but more or less yes. fastboot flashall is typically used to flash the recovery partition only to boot from there and continue with sideload (see 1.).

3. There definitely are, but I'm not able to do it on my own. The referred utility does exactly that. It should be possible to figure out the exact commands or find a similar utility for your manufacturer. I misused mine to flash everything I needed for me. To do so, i just replaced the respcetive .img files such as boot.img