How to diagnose why a computer is running so slow?

Generally, what are some ways to diagnose why a computer is running so slow? To find out whether it is because of insufficient memory, busy CPU, or some other reasons? What are some distinct symptoms of each cause?
For example, my Ubuntu is now using 1.2 GB out of 1.9 GB RAM, 1.7 GB out of 3.8 GB swap, and Dual core CPU's usage is about 75%. Switching between programs can take long. Sometimes keyboard doesn't respond, but it is fine itself.
I think I have a big lesson. My laptop is Lenovo T400, bought in 2009. It was fast at the time, but it gradually became slow, probably because the internet has changed so quickly, and a lot of memory consuming features have been adopted. So in general, how do you realize you have to update your hardware in time?

Thanks!

Ben

Posted 2013-12-19T02:33:49.850

Reputation: 1 655

Are you using the 32-bit or 64-bit version of Ubuntu? I have a T400 also, and it still runs 32-bit versions of Ubuntu 10.04, Win7 and XP Pro as fast as when new. Have you checked the health of the hard disk using smartctl -a /dev/sda? – sawdust – 2013-12-27T23:54:54.290

32-bit Ubuntu 12.04 on T400. – Ben – 2013-12-28T00:22:57.257

Answers

More RAM would increase multitasking capability since it wouldn't have to use the swap partition, but a dual core processor(depending on the clock speed) also isn't going to cut it if you really care about speed.

user270595

Posted 2013-12-19T02:33:49.850

Reputation:

thanks. (1) my cpu is Intel® Core™2 Duo CPU P8800 @ 2.66GHz × 2. Is that slowing my computer down? (2) Sometimes keyboard doesn't respond, but it is fine itself. Can it be because of RAM? (3) Ideally how to tell if RAM is suffcient? when swap isn't used at all? (4) I think I have a big lesson. My laptop is Lenovo T400, bought in 2009. It was fast at the time, but it gradually became slow, probably because the internet has changed so quickly, and a lot of memory consuming features have been adopted. So in general, how do you realize you have to update your hardware in time? – Ben – 2013-12-19T02:46:15.150

@T... Well you could replace Uniy with something lighter like XFCE, according to Moore's law processers double speed every two years, but since it's Linux which is generally pretty light it might be better to increase your RAM first, since RAM can be replaced without buying a new laptop. – None – 2013-12-19T02:51:51.040

Ideally how to tell if RAM is suffcient? when swap isn't used at all? – Ben – 2013-12-19T03:05:58.070

Reinstall your Operating System. All operating systems just get bogged down with tons of crap over years of use. It never ceases to amaze me how well this still works to this day.

MDT Guy

Posted 2013-12-19T02:33:49.850

Reputation: 3 683

Reinstalling an operating system is overkill for an unknown problem which could be in any layer of the software or hardware, including hardware faults, application bugs or misuse, old hard disks, or a thousand other things which reinstalling the OS won't fix. – Jack Wasey – 2018-04-06T18:14:55.280

But my OS is Ubuntu 12.04. – Ben – 2013-12-19T03:15:02.587

1well there's your problem! – MDT Guy – 2013-12-19T03:15:26.363

What problem is mine? – Ben – 2013-12-19T03:16:01.450

1nevermind, your options are really limited, try a clean wipe and a fresh install of the latest release of Ubuntu? – MDT Guy – 2013-12-19T03:34:04.827

I'm surprised no-one has mentioned the typical tools you use to start tracing this problem. These include (among others) vmstat to measure what part of your system is underperforming and top to see what programs are eating most resources.

The amount of swap being used is alarming and points to your problem, but the amount of memory being used is not (memory is cached and counted as used). You might want to see how much of your memory is actually in use and how much is buffers/cache - the Free command can tell you this. If a lot of memory is cache you may want to change the "swappiness" of your system so it uses less cache - this can make a huge difference when doing things like web browsing.

davidgo

Posted 2013-12-19T02:33:49.850

Reputation: 49 152

First, get the CPU monitor gadget to see when it is going slow. 1. See if you have too many programs (probably the leading cause of computers going slow) 2.Defragment your hard drive, it puts all the pieces of your files (fragments) and puts then back in place, it will stop your computer programs from going slow 3. Check for viruses, I recommend using AVG internet security 2014. It is scanning your system all the time. If you go on a malicious website it will stop it from opening. That is pretty much it Good luck with your computer problems.

Alex Alomar

Posted 2013-12-19T02:33:49.850

Reputation: 7

Does Linux have to degragment? – Ben – 2013-12-19T03:05:20.410