In simple terms, Ecus are just boxes with numbers stored in them !!

The L6 has 8192 numbers to store program and maps (bytes)
The L8 has 16384 bytes
The P8 has 32768 bytes

Not all are used in the chip but very nearly.

My own ecu has 512000 ROM bytes, 256000 RAM bytes and
1024000 flash memory bytes (1 megabyte) not to mention 2 x 32 bit processors.