A brand new and shiny phone, right from the store. After the phone boots up for the first time, the phone will slow down as it ages.
Even the most powerful of phones that are on the high-end range with the most cores and processor ability, the most memory and storage capacity, will eventually slow down. From the most expensive iPhones to the cheapest of Android phones. All of them will experience the inevitable, as they will slow down the more they are used.
So why is this happening?
Short answer: nothing lasts for eternity.
Long answer: the reasons come from the way the hardware is designed, and how the software works.
Both of a phone's hardware and software contribute to its performance issue.
First off, smartphones have various sensors, powered by numerous components.
While most smartphones don't have moving internals, like fans, they have components that are made by tiny materials that will degrade.
Electrolytic capacitor for example, can dry up eventually, and lead to read and write issues. And if the resulting faults make algorithms to run unexpectedly, the results will degrade the phone's performance.
Then on the storage department, SSD experiences what it's called the Write amplification factor (WAF), which is a numerical value that represents the amount of data a solid state storage controller has to write in relation to the amount of data that the host's flash controller has to write. With less free space on a highly I/O intensive system, the SSD can see some extra overhead, which increases WAF. And in time, a SSD drive can spread out data in different location, creating even more WAF, which in turn will degrade performance.
The processor can also degrade its performance, especially when it is continuously exposed to heat. And when dust particles make their way inside the phone, the build up can lower the contact surface of the cooling system, increasing the heat, and forcing the processor to slow down even more.
Another hardware issue, is the battery. This component degrades fast due to Lithium-based chemical problems.
Smartphones have sensors that manage the battery and its usage level. If the battery's maximum capacity has degraded, the phone will require more frequent charging that it normally would. And this will program the processor to reduce its clock speed, in order to preserve the battery to last as long as it can.
This also degrades performance.
On the software side, there are plenty more where that came from.
First and foremost, is the memory leak issue.
Smartphones are computers that are shrunk in size. They operate in roughly the same way as their bigger PC counterparts, but using much tinier components.
Those components are packed so densely inside a smartphone, and with the advancements of technology, they don't necessarily need any moving parts. Operating without a sound, smartphones don't need to rest.
They can be on as long as their users want them to, and they will do that just fine.
However, phones that are turned on for a prolonged period of time will suffer from the memory leak issue, in which the phone's system will incorrectly manages memory allocations, in a way that a memory that is no longer needed, is not released.
This memory leak happens because the system that detects the depleting memory will try to reduce background activity or speed in which it needs to operate, in order to conserve the resources it has left.
Memory leak can also happen when data is stored inside the memory, but the data can no longer be accessed by the running code.
What users will experience when their device is leaking memory, is a slowing performance.
Also on the software side, is the operating system itself.
The moment Apple and Google release new versions of their operating systems, the moment is also the time when a slew of people started claiming that their old devices have started to lag.
New major versions of iOS and Android bring lots of improvements, additions, bug fixes, and more. They can also include design changes as well.
While new versions of the operating systems are meant to bring everything to a whole new level, the fact is that, the updates are meant to work towards two main goals.
First, is to support new hardware and chips, so the software is at its maximum potential on new phones that just hit the market. The operating system focuses to maximize the potential of new hardware and components, so phones can run blazingly fast.
Second, the operating system also needs to work on existing phones running on older hardware components.
The issue here is that, older phones may not support new features that are brought by the newer operating system versions. What this means, older phones may consider the newer operating systems to have some bloat codes they cannot use.
Long story short, the latest versions of an operating system are designed to focus on newer hardware and newer devices. As a result, it can't be helped that older phones that cannot make use many of the codes, will experience degrading performance.
In fact, phones being slowed down is may be done on purpose. Back in 2017, Apple admitted that it intentionally slowed down some older iPhones to “prolong the life” of the devices, by helping the batteries age slower.
If this is the fact, so why would Apple and Google do such a thing?
Since software development is expensive and it's difficult for Apple and Google to maintain too many sub-versions of an operating system, their best option is to deliver operating system updates and features that work best with the latest hardware, even if this should leave old devices behind.
The truth is that device manufacturers are in the business to make money. And here, they know that most consumers don't really stick to their old devices for too long. This suggests that manufacturers are not intentionally slowing phones down, but are prioritizing the latest release so people will buy it.
This is why, a phone that is kept in its box running its original operating system should, in theory, run well for a long time.