Multitasking in Smartphones
Apps in smartphones that run in the background do not always display multitasking. They can be in three states: running, suspended (sleeping), or closed. When an app is in the running state, it is in the foreground and you are using or interacting with it. When an app is running, it works more or less like apps do on computers, its instructions are executed by the processor as it consumes space in memory. If it is a network app, it can receive and send data. Most of the time, apps on smartphones are in the suspended (sleeping) state. This means they are frozen where you left it; the app is no longer being executed in the processor and the place it occupies is in the memory. In this case, the data it holds in memory is temporarily stored on secondary storage (an SD card or the phone’s extended memory—analogous to the hard disk on a computer). When you resume the app, it returns you to where you left off, rescheduling its instructions to be executed by the processor and bringing back the hibernating data from secondary storage to main memory.
Multitasking and Battery Life
A sleeping app consumes no processor power or memory, accepts no connection, and consumes no additional battery power. This is why most apps for smartphones adopt the sleeping mode while asked to run in the background; they save battery power. However, apps that require a constant connection, like VoIP apps, should be kept in the running state, which drains the battery. This is because if they are sent to sleep, connections will be refused, calls will be declined, and callers will be notified that the recipient is unreachable. Some apps must run in the background, performing real multitasking, like music apps, location-related apps, network-related apps, push notification apps, and especially VoIP apps.
Multitasking in the iPhone and iPad
It started in iOS with version 4. You can leave the running app and switch to a background app by going to the home screen. Notice here that it is different from closing an app. If you want to resume with an app in the background, you can use the App Switcher, by double-pressing the home button. This brings the focus to an array of app icons currently in use while blurring the main menu. The icons that appear are those left open. You can then swipe to run through the list and select one. iOS also uses push notifications, which accept signals from servers to awaken apps running in the background. Apps receiving push notifications cannot go to sleep completely because they need to remain in the running state to accept incoming messages. You can choose to close apps in the background by using the long press.
Multitasking in Android
In versions of Android prior to Ice Cream Sandwich 4.0, pressing the home button brings a running app to the background, and long-pressing the home button brings up a list of recently used apps. Ice Cream Sandwich 4.0 changed things a bit. There is a prominent recent app list that gives you the impression of managing the apps, but that’s not the case. Not all apps in the recent list are running—some are sleeping and some are closed. Tapping and selecting one app in the list might spring up from a running state, or it might wake from a sleeping state, or load the app afresh.
Apps Designed for Multitasking
Some apps are designed to work in a multitasking environment. An example is Skype for iOS, which has new capabilities for handling notifications and remaining active in the background while using minimal battery power. Skype is a VoIP app that allows voice and video calls and needs to remain active always for a better user experience. This works much like a mobile phone, which is always checking for signals from incoming calls and text messages. Some users want to disable multitasking on their devices, probably because they find that apps running in the background slow down their machines and consume battery life. This is possible, but operating systems do not give easy options to do that. For iOS, it may require jailbreaking the phone.
