The installer sets this variable to the amount of physical memory, in megabytes, of the target system.
Note: Windows typically underreports the amount of memory slightly. For example, a system with 512 MB of RAM installed may be reported as having 511 MB. Please bear this in mind if you use the PhysicalMemory variable in conditional expressions.
You can refer to it as <PhysicalMemory>. In conditional expressions you can omit the brackets and use tests like PhysicalMemory >= 255. Do not set this variable directly; it is set automatically when the installer runs.