While a process is running, most of its data is held in main memory, which is usually some kind of random access memory (RAM). On most current computers, main memory is volatile, which means that when the computer shuts down, the contents of main memory are lost. A typical desktop computer has 2–8 GiB of memory. GiB stands for “gibibyte,” which is $$2^{30}$$ bytes.
If the process reads and writes files, those files are usually stored on a hard disk drive (HDD) or solid state drive (SSD). These storage devices are non-volatile, so they are used for long-term storage. Currently a typical desktop computer has a HDD with a capacity of 500 GB to 2 TB. GB stands for “gigabyte,” which is $$10^{9}$$ bytes. TB stands for “terabyte,” which is $$10^{12}$$ bytes.