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In general, to save a few CPU cycles, turn off special effects for the UI and use a native skin. Additionally, put the cache on a drive different to windows (see Opera7Tips for how) and keep the drives well defragmented (as the cache is writing and deleting pages constantly - so benefits greatly from a defragmented drive). Some people change the process priority of Opera to get a further enhancement (set to 'high'), but do this if you are predominantly only using Opera (to change process priority in win9X, try this program, 2000/XP can do this natively). Users of old computers should turn Java off and probably javascript too by default unless a page requires it. Remember F12 toggles these settings easily and quickly.
Cause: Lots of pictures take more memory / CPU, which is more difficult for older computers to render.
Solution: Opera gives you the choice to save some memory and CPU by not pre-drawing the images before you see them on the page. The benefit is less used resources, but graphics may 'pop' onto the screen rather than smoothly scrolling into view. If you want to save memory and resources, set Preferences » Multimedia » Draw Images Instantly to OFF. Remember also that g toggles graphics between off/cache/on - you can use a default of cached only and this will greatly speed up page load, pressing g to load any images (or right-clicking individual pictures and selecting Load Image). It is also possible to press Shift+g to load all images on the page that requires images to be displayed.
Cause: Opera uses a progressive rendering technology which actually speeds up the time it takes to get readable text content, but at the expense of the page redrawing each time some new information is added. Many users perceive this to be actually slower when they see the content redrawing, even if when timed objectively, it is faster. Opera gives you the choice about how you want it to load the page, depending on what you perceive as faster!!!
Solution: If you would rather read the text quickly at the expense of the page redrawing more, set Preferences » Windows » Loading to "redraw instantly". If you would rather wait (to see more smooth loading behaviour), then increase this setting according to your taste. Users on slow connections but fast computers should set this about 1-2 second, slower computers on slow connections about 2-3 seconds. If you have a fast connection, most data should be in by about 1-2 seconds, so set to "redraw instantly" (or "redraw when loaded" if you want it super smooth!). If your fast connection is linked to a slow computer, then set it from about 2 seconds up ("redraw when loaded" should be good in this case) to minimise lots of page redrawing.
Cause: Incorrect settings for "Max connections to a server" in Preferences » Network. See HttpProtocol for technical details.
Solution: Web standards suggest a browser should use no more than two persistent connections per server[1]. Opera's default is 8 connections per server (although only half of these are persistent at any one time[2]). Many users increase the number of "Max connections to a server" thinking it will make Opera faster. Often too many simultaneous connections actually slow down the time taken to load a page (servers can deny lots of simultaneous connections, and the time overhead to make lots of new connections takes longer than if data was pipelined on a single/few connections). If you get Opera hanging on parts of a page, reduce this number back to 8 or 4. You can keep the "Max total connections" higher, and this number depends on the bandwidth/speed of your internet connection. I've used 32 with no problem on dial-up. If you open lots of pages simultaneously, try increasing this number.
[1] HTTP/1.1 Protocol, Chapter on persistent connections.
[2] See this newsgroup article.
Cause: Incorrect settings for "Max connections to a server" in Preferences » Network.
Solution: On slow/busy Internet connections having too many connections (more than 8) open may lead to some of them timing out. Setting the number of "Max connections to a server" to a lower number (2-4) makes Opera queue the requests and they won't time out. Decreasing the number of connections on a slow (dial-up) or busy (shared connection or P2P is heavily used) Internet link will not make downloading slower, but it will prevent connections timing out.
Cause: By default, Opera searches for networked machines when resolving a typed in address, slowing down the time taken to find the right address. Virtually no one uses this network search, so it should be turned off.
Solution: Preferences » Network » Server name completion » Disable 'look for local network machine'. Turn off name completion too if you don't use it.
Cause: Inefficient Cache settings. The cache stores information from the web locally on your computer so if you need the information again, it comes from your computer and is much faster. If the information has changed, Opera must decide how often to check if there is new information that must be downloaded. Another benefit is that you can browse pages offline using the cached page.
Solution: The cache in Opera allows fine adjustment to get the most out of it. The settings you choose depend very much on how important it is for you to see the 'latest' version of a page. If that is you, then disable the cache entirely, but remember you will get slow performance (and detrimentally increase traffic on the internet, not good netizen behaviour). If you want to optimise your performance (and be a good netizen), then set the cache to the following (preferences » History & Cache):
Cache Documents: ON
Cache Images: ON
Cache Others: ON
Empty on exit: OFF
Check documents: Every 5 hours
Check Images: Every 24 hours or every week
Check Others: Every 10 or 24 hours
Always check redirect: leave both on for compatibility, and both off for possibly slightly more performance.
REMEMBER: If you want to check if a page has been updated, then press F5 to reload the page from the web, if any information has been updated, those new parts will be downloaded and displayed fresh (things that are unchanged are not downloaded again).
Cause: Opera 7.x can be slow to start if you have a large global.dat file (found in your profile directory. If this file is larger than 100K, the slowdown is noticeable, if it's +500K, startup time may be as long as 20 seconds.
Solution: Preferences » History and cache - change "Visited addresses" to the maximum of 500. Try clearing history (Preferences » History & Cache and 'clear' Visited addresses, to regenerate this file anew. Also try deleting global.dat manually in case it has become corrupted.
Cause: Some people still find that a large cache can slow down the starting time of Opera - or that dcache4.url may be corrupted.
Solution: Preferences » History and cache - lower "Disk Cache" size, or if you don't mind losing the speed up to browsing (which I would) - you could "Empty on exit" the cache. Remember lowering the disk cache size/emptying on exit will slow down browsing and put more load on the internet, so this is a balance (I'd much rather have faster browsing and slower startup personally). To see whether your cache index is corrupt: empty the cache (File » Delete Private Data), then find where the cache is located (Help > About) - and use your file manager / explorer to go to the cache directory and delete the dcache4.url file.
Cause: Opera scans the fonts folder prior to startup, and with large fonts collections, startup therefore takes longer.
Solution: Opera scans the fonts folder on startup, presumably looking for display fonts and fonts for international charactersets. Large font collections also slow Windows down, and so using a font manager is highly advised. Font managers (see a list here), apart from usefully organising and managing unweildly font collections, allow groups of fonts to be dynamically loaded/unloaded, thus using up less resources and resulting in faster startup times. Someone has also suggested in turning: Control Panel » Fonts » Tools » Folder Options » Truetype Fonts » "Show only truetype..." on as possibly speeding up Opera start times.
Cause: active skin is unpacked (not compressed)
Solution: After you unpack a skin to modify it, make sure to compress it back into a ZIP file. Opera is able to load a skin from an uncompressed directory, but it takes a LOT longer.
Cause: Opera disables HTTP 1.1 by default for proxies (as not all proxies are compatible), thus slowing network performance down.
Solution: Go to Preferences » Network » Proxy Servers and turn "Enable HTTP 1.1 for proxies" on. If you use TheProxomitron, also turn off "Local connections persist..." as this (bug) actually turns off outbound HTTP/1.1 from the Proxomitron to the outside web!
Cause: Insufficient system memory.
Solution: File » Preferences » History and cache - disable Automatic RAM Cache, set it to a smaller size if you have limited memory. Here are some rough estimates:
RAM Cache 32 Mb OFF 64 Mb 4 Mb 128 Mb 10 Mb 256 Mb 10 Mb 512 Mb 20 Mb 1024 Mb 40 Mb >2048 Mb 60 Mb
Solution: Make sure that Preferences » Network » Synchronous DNS is turned OFF. If you use Windows 95, however, you need to leave it on. Any other Windows version can have it off without any problems.
Cause: Too many plugins.
Solution: Type in opera:plugins in the address field, you'll see a list of loaded plugins. Which of those do you really need? Delete unnecessary plug-ins (for example you don't need any Java ones), or add the file names to plugin-ignore.ini if you are using them with Netscape.
Cause: Slow computer may not always be efficient to smooth scroll graphics heavy pages.
Solution: Disable smooth scrolling (Preferences » Windows » Smooth Scrolling) — may solve some rendering issues too.
Cause: Video adaptor problems.
Solution: Is your videocard overclocked? If so, try to stop overclocking it. Try to decrease "Hardware acceleration" in your adaptor properties and see if it helps. Try to upgrade (downgrade?) your drivers. This can also stop crashes.
Cause: JRE 1.4.1_02 / 03 is unstable with Opera on some systems.
Solution: Install the latest "The J2SE Runtime Environment".
http://java.sun.com/j2se/1.5.0/download.jsp
¿Possible Cause?: Packed EXE and DLL files (using ASPack).
Solution: If you are running a anti-virus that checks files in real-time "on open", this may become a issue (although users disagree strongly on this). Kaspersky is one example of such software that some users have had trouble with. If you are worried, try to setup your AV software not to monitor Opera folders. This type of checking could considered over-paranoid and slows down your system somewhat. Note that you will increase your vulnerability to infection. Because this is a very unlikely source for any performance problems, it is almost certainly not worth the extra risk involved .