Question: How do phones work

Gary Munnelly answered on 8 Nov 2018: last edited 8 Nov 2018 2:17 pm

OK, for modern smartphones, this question basically decomposes into two parts:

1. How do smartphones run apps, browse the Internet etc
2. How to smartphones make phone calls

In answer to the first part, smartphones are basically just like any modern desktop computer or laptop. They have a CPU and some on-board memory which stores the operating system, your photographs, phone numbers etc. There is also a variety of hardware installed to do things like transmit and receive bluetooth signals or broadcast a WiFi signal if you want to hotspot from your phone. There are special programs called “drivers” that are installed along with the operating system which tell the OS how to interface with those pieces of hardware.

When you turn the phone on, a special program that is baked directly into the hardware runs and identifies where the operating system is installed. It sets up a few locations in memory with special values and then hands control over to the OS which starts drawing things on your screen, running your apps and waiting for you to interact by touching the screen (or “Digitizer” as Dimitar pointed out it is called).

Whenever you do something with a part of your phone, the appropriate driver tells the OS how to interpret your interaction and the OS figures out what to do from there. For example, if you press a button to turn off your phone, then the driver tells the OS to shutdown and the OS begins turning off. If you are playing with an app and you touch the screen, then the driver tells the OS where you are pressing and the OS transmits that information down to the app which is running as a process. The app updates and the screen is redrawn to reflect the changed state of the phone.

For the second point – how does your phone make calls? There is a special piece of hardware installed in your phone which can communicate with the cellular network of your mobile service provider via an antenna or arial. The OS knows how to use this hardware because there is a driver installed on the phone which tells it how to use it.

When you make a call, the phone contacts the nearest cellular tower of your service provider and supplies credentials for your account which are obtained from your sim card. There is some checking done on the part of the tower to make sure that you are actually a customer of that provider and that you have enough credit on your account etc. If all is good, then the tower broadcasts your message to the phone that is identified by the number you dialed. Messages between you and the person you called are routed back and forward via the tower. Sending text messages works the same way as does browsing the Internet when using mobile data.

This is actually an amazing thing, because back in the early days of phones, the phone had to be wired directly into the network. There were no wireless cellular towers and phones all had cords. When you made a call you would speak directly to someone working at a switching station who would have to physically wire your call to the person you were trying to contact. Crazy how science fix dat.

Explaining how a phone works is a really big question and this answer barely scratches the surface, but I think that broadly covers the major points of how a phone works.