external storage; auxiliary storage
Computing term for non-main memory used for long-term data retention, such as hard disks, SSDs, or USB drives.
I use an external hard disk as auxiliary storage.
主記憶 refers to main memory (RAM), while 補助記憶 is auxiliary/external storage.
auxiliary storage; secondary storage
Compound of 補助 (ほじょ, 'assistance, auxiliary') and 記憶 (きおく, 'memory, storage').