'non-buffered' is formed from the prefix 'non-' (from Latin 'non', meaning 'not') attached to 'buffer' (English noun/verb).

'buffer' comes into English via Anglo-Norman/Old French (e.g. 'buffe'/'buffer') meaning a pad or blow; the verb 'to buffer' and its participle 'buffered' developed in modern English; adding the negative prefix 'non-' produced the compound 'non-buffered'.

Originally 'buffer' referred to a pad or cushion and later to a device or memory area that cushions or holds data; 'non-buffered' thus literally means 'not having that cushion/buffer' and evolved to denote direct/unmediated handling of data or operations.