FAQ
FAQ
Cache settings
What options are there for the cache?
Opera 5 gives you independent control over the RAM and Disk caches, and has the ability to check remote files and see whether they've been updated since last being cached:
Disk cache
You can limit the amount of disk space Opera will fill with cached files while you browse, and select which out of HTML files, images, and other Internet files will be cached to disk. You can also set Opera to wipe the entire cache and free up the disk space every time you close the browser.
Increasing the cache limit and saving the files on exit may be of use if you regularly visit several sites on your Symbian device. Layout images, stylesheets and other files which are shared by the pages of each site will then be available instantly, reducing download times considerably. However, if running low on memory then reducing the limit will help prevent Memory low
errors and crashes. If you only use Opera for casual browsing you may also want to empty the cache on exit to free up more memory for other applications.
RAM cache
Opera 5 allows you to set separate RAM cache limits for both HTML files and images, but it also offers an automatic mode where Opera will try to guess which files are worth keeping in RAM for faster access. Turbo mode is available to allow rendered images to be cached, further improving performance, though this is less memory efficient.
Other options
A potential problem with caching is that a file on the server may be updated while the browser continues to display an old copy cached during a previous session. The usual way to check this is for the user to click the browser's reload button and force a refresh, however Opera 5 has the ability to check whether files have been updated on the remote server since last being cached. If they haven't, Opera will display the cached copies rather than wasting time downloading the same files all over again. Opera gives you independent control over checking HTML files, images, URLs that redirect you to another file, and other Web-related files such as external stylesheets and Javascripts.
This option isn't foolproof however and it does slow down Opera to some extent (though not as much as reloading the page). In order to determine whether a file on the server has been updated, the server must have sent out a Last-modified
HTTP header when Opera downloaded it originally. This date is then included in Opera's next HTTP request for that file and the server compares it with the Last-modified
date of the current file. If both dates match then the file cannot have been changed and the server will signal this to Opera, resulting in the cached file being displayed instead.
If the server didn't send out a Last-modified
header, or server scripting is being used to generate pages omitting this header (a common oversight by authors), Opera will have to assume the page has been changed and download it again anyway.
Depending on your connection speed and that of the server, it may take around half-a-second for Opera to connect to the server and check each file. If a page contains many images and Opera is set to check them, there will be a delay before cached images appear on the screen. To improve performance, users may prefer to check modified documents but not images.
Note that for Opera to check for modified files it will require an Internet connection. If you are browsing cached files while offline then Opera will attempt to go online again unless you are in Offline mode.
Can I move the cache to another drive?
There is no option for this in Opera's preferences, however there is a fairly simple workaround. Make sure Opera is fully closed and using a plain text editor (Symbian Editor is recommended), open the following file:
If you're using Symbian Editor you can simply click on the file from the System screen to open and edit it. If you're making do with Word then you'll have to move the INI file to your Documents folder first, and import it into an empty Word file from there.
When you have opened the file, scroll down to find the [USER PREFS] heading and add the following line to the list of settings below it:
CACHE DISK=D
You can substitute D
for a drive of your choice if one is available on your Symbian device. If using Word then you'll now have to export the file as plain text and overwrite the original INI file. After that, move the updated Opera.ini back to it's original location. If you have edited the file in place using Symbian Editor then simply exit to save the changes.
When you next start Opera, the new drive will be used to store Disk cache data however it will not automatically move previously cached files from the internal disk to the new drive. These files will be ignored, waisting disk space, so either delete the following folder and all of it's contents or move it manually to the equivalent location on the new drive before starting Opera:
Be careful not to delete any other system files in the Opera folder.
Note that on most Symbian devices, extra drives are usually flash memory in the form of a CF card, Media card, or similar. These cards are considerably slower to access than RAM so moving Opera's Disk cache to one of these drives will slow down the browser. Expansion cards also consume more power than the internal drive so battery life may become affected. When battery levels become fairly low the device may start to produce errors reporting that it was unable to write to disk, and until new batteries are fitted or the machine is recharged Opera may no longer work. On extremely rare occasions, attempting to write to flash memory while insufficient power is present can result in loss of data or even the corruption of an entire disk.
What's the difference between Disk cache and RAM cache?
Opera's Disk cache is made up of temporary Internet files which Opera stores individually in a folder on a drive, and then retrieves as they're needed. These files will appear in the file system just like any other document or file (though they're hidden in the System folder) so they can be kept after you close Opera and viewed again in the next browser session. When Opera is running on a machine with a physical hard drive, such as a desktop PC or set-top box, these files will be accessed relatively slowly.
RAM cache also contains temporary Internet files, however they are kept in your machine's RAM for the duration of the current browsing session. They do not appear on the file system and the RAM will be freed as soon as you close Opera. The benefit of RAM cache is that it allows data to be retrieved instantly, so allocating a little RAM cache can give Opera a noticeable performance boost, especially when combined with Turbo mode.
If Opera is set to save cached files when you exit then all RAM cache data will be copied into the Disk cache folder (as individual files) as Opera closes. When you next start it, Opera will access those files as normal Disk cache data.
Because of the way many current Symbian devices are designed, RAM cache may be of limited use however. Most devices running ER1-5 use RAM both to store the internal 'drive', and for memory to execute programs in. This means that Opera can load files from the internal disk almost as quickly as those held in RAM, with only a nominal delay occurring while the Operating System reads from and writes to the file system.
Flash memory is notably slower than RAM though, so if you've moved the cache to another drive that uses a CF card, media card or Microdrive then the RAM cache will once again improve Opera's performance.
Modern Symbian devices running ER6 and above may implement high-speed RAM only for running programs, and separate, slower flash memory for the internal drive so that data is preserved when the battery is removed. On these machines, RAM cache will also offer speed improvments whilst browsing through sites.
Can I view the contents of the cache?
Yes, you can easily see what files are currently held in both the Disk cache and RAM cache by selecting the Cache option from the Tools/Special-window menu. This view will show a table listing all currently cached files, their temporary names on the file system (eg. opr000F4.htm), their size in bytes, and the full URL of the original file presented as a link so you can go directly to it and reload:
| Filename | Size | Location |
|---|---|---|
| opr000F4.htm | 23456 | http://www.opera.com/symbian/ |
| opr00022.htm | 12345 | http://www.symbian.com/press-office/2002/pr020424b.html |
| opr001A7.gif | 8921 | http://www.google.com/images/logo.gif |
| opr0008 | 2041 | http://www.w3.org/StyleSheets/home |
You can also view the cache by entering opera:cache into the Address Bar, or by following a link that uses that URL. Note that the cache view is a self-generated HTML file and can itself be cached. If you use this option regularly you may need to use Reload to update the list.
What is the cached rendered images
option?
This option is traditionally known as Turbo mode
and it allows the browser to display cached images more quickly by retrieving fully decoded JPG or GIF files from RAM, rather than having to decode the original, compressed file from disk every time it's rendered. The trade off for this improvement in performance is that Opera requires considerably more RAM while running with images enabled. By caching decoded images, fewer files will fit in the RAM cache unless you raise the image limit to compensate.
