CPU cores & Hyperthreading
Some newer CPUs, like the Intel Xeon “Nehalem”, sport a technology called Hyper-Threading which allows two threads to run simultaneously on each core. macOS presents this as 2 virtual cores per actual core, meaning a 4 core CPU will appear as 8 cores. So it’s normal for some Macs to appear to have twice as many cores in iStat and other system monitoring apps.
iStat Menus 5 users can combine virtual cores using the Combine logical (Hyper-Threading) cores under the CPU & GPU tab.