MS-DOS was a single core OS and does not knows something about multiple cpu's or cores. If you start MS-DOS, it will use the cpu and this means ever with all available cores. You can fix this via task-manager and change the affinity for the process "vmware-vmx.exe" to one core. Or you set the affinity inside your VMX:
processor0.use = "FALSE"
processor1.use = "TRUE"
processor2.use = "FALSE"
processor3.use = "FALSE"
With this setting inside a virtual machine config (VMX), the VM will run only on the second core. You can verify this via task-manager.