その原因は色々あります。例えば、メーカーによって、ウイルススキャナーが一所懸命ウイルスのスキャンをしている間は、システムの反応が遅くなる場合があります。また、アプリケーションによって、巨大なメモリを使うこともあります。
しかし、一つ日常に遭遇する使い方でコンピューターが簡単に遅くなってしまうことがあります。それは、インターネットブラウザーです。そう、その何でもないアプリケーションは、実はメモリを馬鹿食いしています。試しに５，６個のタブを開いてみて、タスクマネージャーで見てみればすぐ分かります。IEであろうが、Firefoxであろうが、Chromeであろうが、皆似たよものです。それで簡単に６００メガバイトかそれ以上メモリが占領されてしまいます。
ホームページによって、１００メガパイと以上のメモリを使ってしまう場合もあります。さらに、プラグインなんかもメモリリークのような動きをし、いつの間にかすべてのメモリを使い果たしてしまうこともあります。それで、システムはハードディスクを仮想メモリとして使い始めて、すべての処理・操作は遅くなってしまいます。
もしXPのユーザーであれば、悲惨なことに、一旦上記のモードに入ると、システムを再起動しない限り、どんなにアプリケーションを落としても、永遠に遅いままになります。
結論、ウェブブラウザーを使う時に、見ないタブをこまめに閉じることです。
[追記]
今日は、一つメモリの大食い王を見付けました。XPのPCでChrome（Ver16.0.912.75 m)を使っていたら、何故かPF使用量は３．５G以上になってしまい、PC全体はめちゃくちゃ遅くなりました。タスクマネージャで見ると、あるChromeのタスクは369MBも食っていることを判明しました（下の画面）。Chromeのプロセスだけで、合計741MB以上使っていることになっています。
そんなバカな．．．!!!!
それで、オープンした7個のTabのどれがその元凶なのかを調べることにしました。方法はタブを一つずつ閉じることです。
あるページまで来たら、タブの終了は全然終わらなくなりました。そこまでは、問題のメモリ大食い王はまだ居座ったままです。そこから不思議なことが起こりました。その大食い王が使っているメモリは369MB徐々に増え始めました！暫く待っていると、４１１MB まで上昇しました。これでは、話にならないと思い、そのプロセスをタスクマネージャから終了させました。
その後、Chromeの別のタブから、「次のプラグインがクラッシュしました：Shockwave Flash」というメッセージが表示されました。そのShockwave Flashはどんな馬鹿なことをしているかはとても想像がつきません。
もっと言う、今のウェブアプリ、ブラウザのプラグインやサーバー上にあるすべてのアプリを含め、作りは想像を絶するほど雑で、品質の「ひん」も言えない粗悪のものです。実情をよく分かったら、きっと大金を払って買った人立ちは激怒するでしょう。
Being a heavy Windows PC user, from time to to time I am frustrated by the slow response of the system. When searching around for the reasons, one common advise is to check for virus or mal-ware. But ironically, adding another piece of software that runs constantly on my PC will only further slow down it. What's worse, nothing evil has ever been found!
One culprit that tends to be forgotten is the internet browser most user use daily. It is true that most of the browsers are making great progresses so that they are more and more user friendly. But everything has a price. The price everybody is paying is the work load it has brought to the computer.
Nowadays, almost all browsers have tab pages for different site visiting. The tab feature is truly convenient because one can keep track of different pages without having to switch or finding widows for each one. But, each innocent looking tab is actually a "memory monster", eating up dozens of mega byte memory. Since the tab feature is so handy, one usually ends up opening many sites with the same browser without realizing it. The result? The browser can easily use a few hundred mega bytes of memory.
For a computer with 4GB on board memory, this does not sound like a disaster yet. But, remember for a 32 bit Windows operating system, only more than 3.2 gigabyte of memory can be used. The operating system by default can use from over 500 megabyte to over 1 gigabyte memory, depending on the versions. If some fancy, but mostly useless default applications (also the notorious services) have been installed, about 1.5 gigabyte memory may have already been occupied.
The other pitfall of the modern software is that every one is designed with the consumption of infinitive amount of on-board memory. Little efforts haven spent on saving required memory. Only the speed of development, outlook of the user interface are pursued to their maximum, but none for the resources (e.g. file size, memory used). As a result, every software including the frequently used mailing software (e.g. Microsoft Outlook), word processing or presentation software (e.g. Microsoft Office) consumes memory like nobody can imagine. In no time since one started one's computer, all of the on board memories are used up. Then, the system starts to use the hard disk as memory, which puts the computer at a speed of stone age.
Things get worse when one try to switch to another software that has been started, but not used for a while. The system then tries to push what is active to hard disk, and load what was in the hard disk back to on board memory, freezing everything on the screen. Sometimes even the mouse cursor.
To prove my point. Below is the screen capture of the task manager on one pc. The "chome" tasks circled in the red lines are by the five (5 only!) tabs in the only one Chrome Window. Why there are 11 of them when there are only 5 tabs?! To dramatize the result, the total memory used is: 19+17+42+23+7+55+33+91+81+194+9=571 mega-bytes! It is not even showing all the memory it is using. Isn't this freaking crazy? This is an example of Chrome, but any other browsers are as bad as this. Maybe there are some funcky options for optimizing memory usage, but who on earth has the time to dig them out?
The conclusion: be aware of the heavy users of your precious memory. When you feels that the computer is getting slow, make sure that you are not opening too many pages with your browser. This can be a very quick solution. And remember that the browser tends to hold up the memory even if most of the tabs are closed. In that case, just close the whole browser, and some times you have to make sure that the (ghost) process is not there by the task manager.
----Updated on Feb.12, 2011----
searchindexer.exe, a program for "windows search" service, takes about 50MB. There has been many posts about how this program consumes huge resources and how beneficial it is to stop this service. But this guy is needed at least by Microsoft Outlook, even for its "quick search".
Talking about Outlook, it eats up about 50MB by just starting.
Internet Explorer (Ver. 8.0.6001.18702) shows 25+88MB of used memory by opening only one page. After opening one more tab and browsing for a while, about 180MB is gone!
With Firefox Ver. 10.0, opening a window with 3 tabs caused a memory usage jump by about 200MB! And right after opening the window then exit the application, 20MB seems to be missing, when checking with the "PF Usage" of task manager's "Performance" tab. Maybe this guy is not precise at all. But one serious problem with many applications is their lack of cleaning up after termination. It simply means that some memory will "disappear" thereafter. As a result, no matter how much memory has been installed, the system will eventually turns into "swap" mode, using hard disk as system memory. All of a sudden, everything becomes noticeably slow. In this case, the "CPU Usage History" of task manager shows very little activities, but all programs seems to be working very very hard, taking long time before responding to any operations.
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