In order to know which architecture your Ubuntu or sld (linux similar distro) is built on, there are two simple ways :
Open up your terminal and issue the following command :
As you can see on the third line above which starts with CPU op-mode(s), our computer CPU supports both 32-bit and 64-bit. If you only see 32-bit then you have a 32-bit system.
Even if you have a 64-bit CPU, remember also to check your Ubuntu architecture whether it i s32 or 64-bit. This is shown in the second lien above which starts with architecture. Here you can see that it is x86_64.
If you see : x86, i686 or i386 then your OS is 32-bit otherwise if you found x86_64 , amd64 or x64 then your Ubuntu is 64-bit based.
2 – Using the Graphical Interface
Open Settings from the Ubuntu application menu :
In the Settings window, click on the Details tab which is displayed at the bottom of the menu. You will end up in the About section as shown below :
As you can see above, you can tell which architecture your OS is based on.