What is Custom ROM?

Basically the android firmwares(referred as ROM) are classified into Stock ROM and Custom ROM

A Stock ROM is the native firmware which comes default on the smartphones and tablets.

A Custom ROM is opensource firmware replacement for smartphones and tablets which are based on the Android OS.

The Custom ROMs offers features and options not found in the official firmwares distributed by vendors( like HTC, Samsung, Sony). In addition to the feature the custom roms comes "pre-rooted" by which the user can have a variety of root apps. Mainly features include Wifi Tethering, Bluetooth Tethering, USB tethering, Overclocking CPU & GPU, performance & graphical improvements over the stock rom. One more important thing is that they have no bloatwares( useless apps that comes with stock ROMs).

With the rapid development of Android over the years, many user want to upgrade their devices to the newer version of Android. But only the phones with high specifications get the OS upgrades and the old devices gets forbidden day by day. By flashing the Custom ROMs even users with low-end phones can enjoy the newer versions of Android.

Pros:

• Has theming capablity
• Performance improvements
• Comes pre-rooted

Cons:

• Improper flashing results bricking your device
• Privacy, Security issues.
• Bugs & Glitches

As the ROMs are updated more often, the bugs & glitches are reduced for every build of ROM. Security can also be improved by using many apps which offers protection.

Here are some of the custom ROMs

• CyanogenMod
• MIUI
• Paranoid Android
• AOKP
• Some modified Stock ROMs
• AOSP ROMs
• Flyme OS
• Lewa OS
• Liquid Smooth
• Slim Bean (only Android versions 4.1 & up)