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I've noticed that, with the advent of 2.0 (maybe earlier), playing the campaign references "streaming data" from the servers.

Since the campaign maps exist locally (viewable within the editor) and are available offline, why does the game need to stream in additional information? What happens if I "Cancel" this?

Screenshot of Starcraft 2 loading page displaying message "Streaming Data: 32/34 MB"; screenshot modified to circle the message

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up vote 11 down vote accepted

Blizzard adopted this model on World of Warcraft and Diablo 3 a while back. It works in co-junction with the launcher for big patches and digital downloads.

The system allows you start playing the game without downloading it entirely. If you reach a point where missing data is required, it will download it then. (It will also continue to download the rest of the data in the background, as well).

I saw the "streaming data" message once after I had already downloaded everything, checking my bandwidth monitors confirmed it was not downloading from the internet.

Therefore, we can conclude that when the "streaming data" message appears the game first searches for the required data locally, if it finds it is available, it then loads it into memory, if it is not, then it can fall back to downloading from the internet.

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Really now? That's good to know, thanks for the clarification, +1 – MapCavalier Mar 12 '13 at 21:35
Surely loading a mere few MB's into memory won't take seconds? (Even with my game at 100% downloaded, that's how long the game tends to stop loading.) – Jeroen Mar 23 '13 at 16:32

This is from the patch notes for the update that introduced this feature:

New Streaming Launcher

A new StarCraft II Launcher will allow game data to stream during play. This should reduce download, install, and patching times. We look forward to your feedback on the new launcher! Please visit the StarCraft II forums to share your thoughts.

These are small updates and patches that don't constitute a full update. They're likely negligible on the whole, so if you were to cancel it you shouldn't encounter any problems.

Hope this helps!

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Are you sure this is for maps? Playing the campaign requires neither further download, install, nor patching. Or is this simply done while maps are loading while the hard drive is busy reading from the installed files? – Raven Dreamer Mar 12 '13 at 2:37
I'm pretty confident this is correct. I anyone finds info otherwise I'll check it out, but this makes good sense to me. – MapCavalier Mar 12 '13 at 2:40
@RavenDreamer It may also be that it "streams" map info from the hard drive. I'll continue to look into it for you. – MapCavalier Mar 12 '13 at 2:43
During the campaign you should only see this once per play through on a given map. – Ramhound Mar 17 '13 at 12:36

I believe that it does not only check if the downloadable cache files are on the disk, but also checks the content of the files by calculating some kind of a checksum. It might be also possible that the downloaded files are digitally signed and it verifies the file signatures before using the files to prevent hacking, modification or piracy.

Merely checking the existence of the files should take only some seconds, but if it also checks the content the files, it can take up to a couple of minutes to verify the files, especially if the game cache files are on a slower HDD.

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