I'm planning to use Multisite to host 200 different wordpress blog with each having their own unique subdomain. I notice each time I create a virtual host for each subdomain it'll use roughly 50mb ram. So if 50mb * 200 sites = 10GB RAM correct me if wrong is 10GB of RAM needed to host 200 sites? if possible is there solutions to decrease ram usage?
The actual RAM you need depends on many factors:
- installed extensions (server and PHP)
- the current operation (editing images needs the most)
- translation, some translation files are really heavy
In a multisite, some resources are shared, the server setup for example is not duplicated each time you create a new site.
The number of sites is unrelated to the amount of memory required. The amount of required memory is (if you are using Apache)
the amount of memory required to serve the most memory intensive page * the number of requests you want to serve simultaneously
Both numbers vary based on the way you set your server and the themes and plugins you use.
Regarding the memory usage of translations (I'd have commented toschos answer, but I'm lacking the needed reputation): That can be reduced using my plugin WP Performance Pack. It offers use of native gettext if available and an alternative MO implementation (if gettext isn't available), which only loads used translations. Both methods reduce memory consumption and improve performance of localized WordPress installations.