The FastCGI module in IIS has a configuration setting maxInstances, which controls the number of concurrently running php-cgi.exe processes that IIS creates to process PHP requests. To achieve optimal performance, it is recommended to fine tune this setting for your specific environment starting with 8-10 instances per CPU core (e.g. maxInstances=32 for quad-core CPU).
Today IIS team has released the beta of the Windows Cache Extension 1.0 for PHP. The Windows Cache Extension for PHP is a PHP accelerator, that is used to increase the speed of PHP applications running on the Windows operating systems. Any PHP application can take advantage of the functionality provided by the Windows Cache Extension for PHP without any code modifications. All that is required is that the extension is enabled and loaded by the PHP engine.