The storage space eventually gets filled up because you keep adding files and programs which require storage space, not because of history and temp files and normal operation. If you don't take the time to occasionally delete things you no longer need/use, you'll eventually run out of room. But the idea that you'll need a new computer every few years is hogwash. If you buy the proper hardware to begin with (a hard drive large enough to accommodate your intended use) and do proper maintenance, a computer should last more than a few years. I had almost 8 years out of my Win98 box before a hardware failure finally doomed it.

Your friend isn't very well informed. It's true that hard drives do fill up and accumulate crap that slow the computer down. But there are ways to clean it up regularly and return the computer to its original performance level. Also, like your car, parts do breakdown and have to be replaced. However, the main problem is that technology and software keeps evolving, so older machines can't keep up as well as newer ones.

Nonetheless, the idea of computers "wearing out" in a couple of years, and there's nothing you can do about it, is simply wrong. One of my computers is ten years old and is still working just fine...although it's not as swift as the one I got a year ago that has more advanced components.

Physically as a system goes, heat and dirt/dust are far more of a concern than "wearing out" if such a thing is possible.

Before this system my prior one was eight years old, and still reliable. It just lacked a lot for today's offerings, both Internet and on-board.

DA

OK, thanks for good info. I have added very few files over the 7 years I've had this e-machine. I simply web browse and then delete temp file. Microsoft, however, has been routinely adding updates, patches and additions to its security program for years. Will these additions amount to a fill-up of space in the term I've had the computer? It seems slower now than it used to be.

when was the last time you opened up the case and did a very thorough clean out of the inside? that is essential, dirt and dustballs can destroy a pc, the heat build up alone is a big killer. That is the first thing to start with.

Updates do take up space but they are essential.

using programs like ATF or ccleaner in the default setting will help a lot, never use registry cleaners!
ATF-Cleaner.

this is an excellent guide that will help you
Help! My computer is slow!

there are many guides for how to clean the insides of the pc this is one
Cleaning the Interior of your PC

Getting The Grunge Out Of Your PC

and running regular scans with malwarebytes free and superantispyware are a very good idea to make sure you do not have any malware contributing to your slow down.
Malwarebytes' Anti-Malware (Win) - Detecting and Removing Malware
SUPERAntiSpyware Free Edition

You never mentioned what brand/model your computer was, what operating system you are using and how much RAM memory you have. Also, would be good if you were to let us know how big the hard drive is and what percentage of it is free or being used

Your friend is correct. It is generally the hard drive that fails. If you have some time you can read what Google says about the life span of hard drives. I don't know of anyone that has more of them.

Here is a link that might be useful: Hard drive life.

Replacing a failed or failing hard drive is easy. The hard drive is only one component of a computer. The computer I am using right now has had the hard drive replaced twice, and because I had everything backed up to an external drive, including the OS, I was able to restore and go on my merry way. I don't consider this computer "worn out".

I would not consider having to replace a hard drive as a computer being worn out. Updating an older pc is fairly easy to do and can keep them lasting a good long time. Adding the max amount of RAM is the first very good option, if the hard drive is running low on space cloning the drive to a larger hard drive is a very good option and hard drives are not terribly expensive. If and when things on the mother board start to break or deterioate then those are things I start to consider as wearing out, however even a mother board can be replaced, but at that point cost vs a new one should come into play.
doing a lot of good housecleaning on a pc and keeping it updated and free of malware and keeping all that excess junk from building up on the drive and you can have a pc that last many many years. Some of mine are quite old and going strong. If it has not been defragged in a long time that is certainly something to consider doing.

I think you mentioned it was an emachine, they are not the highest quality product and some of their stuff has had negative reviews, it would depend on your model, your RAM your hard drive capacity etc.
Run a belarc on it and that can tell you a lot of info and you can provide some of that here to give us more ideas.
Belarc Advisor - Free Personal PC Audit

making sure all the essentials are fully updated too
Secunia Online Software Inspector (OSI)

My Dell is 7 years old and running like a champ. When I had some 'issues' Dell walked me through wiping it clean and reloading the Operating System...then it was really like now.

If/when I have issues again, chances are if it isn't hardware related, I will do the same thing again, if need be.