The maximum cache size on 32-bit Windows is approximately 1.2GB. This is the largest contiguous block of memory in the 2GB process address space which can be used for constructing a memory mapped file. Due to fragmentation of the process space caused by the loading of libraries required by the digital signature verification code, any attempt to specify a cache size greater then 700MB will result in the automatic disabling of the signature check. Significantly larger cache sizes can be used on 64-bit Windows.
On 32-bit systems that have Apple Bonjour 1.0.6 installed, the maximum cache size is further constrained due design flaw in the Apple mdnsNSP.dll which is injected into all processes that use network services. On these systems the maximum is approximately 512MB.