The internal memory corresponds to the processor registers. And characterized by high-speed access, high cost and limited space. These normally are made with SRAM.
The main RAM memory space is characterized by much higher than that of the internal memory, has the highest access time and is normally made with DRAM integrated circuit.
The secondary memory is characterized by huge space, but very long access times, access is defined by interface software and is made in the form of magnetic disks.
Offline memory requires user intervention to its activation and is usually made with tapes and optical disks. Between internal memory and main memory cache is normally interposed.