Why do computers become slow over time (HW PoV)?

Question

I'm a SW engineer. I'm just curious why computers become slow over time.

"Slow" here I mean from a usual user PoV:

• It takes more time to launch an application.
• Application UI takes longer to respond user interactions. Sometimes even freeze and unresponsive.
• Playing video files on local HDD becomes noncontinuous.
• Sometimes I type some text in "Notepad" program, when I finish pressing the keyboard, the characters have not shown up completely.
• etc.

Of course, I googled. I know Wintel alliance. But I have downgraded Windows to an old version. That does not mitigate. As a SW engineer, I'm not satisfied about the sayings that SW needs more HW resources, malware, etc. That does not explain my confusion.

I'd rather believe that it is HW performance degrading. But I cannot explain why.

I have an old PC which was bought at the same time as Windows 7 released, i.e., late 2009:

• HW: Intel Pentium T4200 CPU, 2GB DDR2 RAM, HDD.
• SW: Windows 7. Lots of application SW.
• Performance: Can play 1080p x264-encoded mp4 videos smoonly.

Now, year 2022:

• HW: Added 2GB more DDR2 RAM, replaced the HDD with an SSD.
• SW: Reinstalled a fresh Windows 7 and disabled Windows Update. Only necessary SW (web broswer and video player).
• Performance: stuck when playing 720p x264-encoded mp4 videos.

Why? Same SW, even "improved" HW, but degraded performance.

Possible factors:

• Heat. Lots of dust cover the fans. That degrades cooling capability.
• Power supply. The well-known "peak performance" issue on iPhone: Apple deliberately lower CPU frequency if battery health is < 80%.

PS:

Same situation with another computer (a mainstream model) bought in 2018. One and (almost) the only difference is that Windows 10 keeps updating over time. Its slowness can be perceived conspicuously by a human.

Answer 1

As mentioned in the comments, this has many open ends but there are certain major aspects which could contribute to slowing down.

1. It comes down to physics. As you said heat. Heat does a lot more than degrade cooling, motherboards are designed to detect temperatures, which on detecting a high temperature the motherboard will signal the components to slow down, which one experiences as throttling. Heat will also cause the components to expand slightly which can cause further degradation. Then there are semiconductor issues to consider like silicon degradation, electromigration, corrosion and even the operating environment of the computer could effect its performance. And if you have moving parts in your computer, they are bound to get slower over time.
2. Your benchmarking the performance is a bit dodgy. Why you might ask, because of point 1 and also because as hardware improves over time, software engineers make modifications in software to take advantage of hardware. It might very well be the case that Windows 7 wasn't optimized for being used with an SSD. Also just playing .mp4 at a resolution makes no sense, as the encoding used for the files matters as well, which would demand extra cpu juice. Even if you browse the web with an old pc, newer websites use a lot more javascript than what they used a decade ago, even if the page looks the same, it will demand a lot more processing power.
3. The underlying design and manufacturing of the cpu and motherboard. Again a broad point but to give some pointers, newer cpus support more instructions out of the box, so for an older cpu might have to simulate an instruction which could affect the performance a bit.
4. The operating system could also be a contributor to degrading the performance. I won't say Windows is bad but it definitely isn't good when it comes to performance(from my personal experience and opinion, comparing the same on a Linux based OS seems more relevant).
5. Other miscellaneous issues, like a damaged PSU, dust accumulation, worn out thermal grease and others, which only you can figure out.