The option that does not belong to the group is "External memory".
Primary memory, main memory, and internal memory are all types of memory that are directly accessible by the CPU (Central Processing Unit) of a computer. These types of memory are volatile, which means that they lose their data when the power is turned off.
Primary memory is the smallest and fastest type of memory in a computer, and it includes the cache and registers. Main memory, also known as RAM (Random Access Memory), is the largest type of primary memory in a computer and holds the data and instructions that the CPU needs to access quickly.
Internal memory refers to the storage capacity that is built into a device, such as a hard drive or a solid-state drive (SSD). This type of memory is non-volatile, which means that it retains its data even when the power is turned off.
External memory, on the other hand, refers to any type of storage that is external to the device, such as a USB flash drive, an external hard drive, or a cloud-based storage service. While external memory can be used to store data, it is not considered to be a type of primary or internal memory because it is not directly accessible by the CPU. Instead, data must be transferred between external memory and primary or internal memory before it can be accessed by the CPU.