/ˈsɛk dɛd/
n. — "Hamming code fixing single bit-flips, flagging double-bit disasters."
SECDED (Single Error Correction, Double Error Detection) uses extended Hamming codes with 8 parity bits protecting 64 data bits in ECC DDR memory, correcting any single-bit error via syndrome decoding while detecting (but not fixing) any two-bit error. Standard for server ECC RDIMMs where syndrome=0 means clean data, syndrome=bit position auto-corrects single flips, syndrome≠0,≠bit means double-error detected—system halts to prevent silent corruption. On-die SECDED variants in DDR5 scrub internal cell errors invisible to controllers.
Key characteristics and concepts include:
- Hamming(72,64) distance-4 code: syndrome decoding pinpoints exact single-error bit, overall parity catches double-errors.
- Server controllers log CE/DE counters, halt on uncorrectable errors—critical for financial/scientific workloads.
- ~1-2% performance overhead vs non-parity DDR, x9 organization (72-bit words) vs x8 consumer.
- On-die SECDED in DDR5 protects internal 128b→120b blocks, system ECC layers on top.
In server read, controller recomputes 8-bit syndrome on 72-bit fetch—if syndrome=47, flip bit 47 and log CE; syndrome=0xFF (no bit match) = DE, halt system before corrupted data poisons caches.
An intuition anchor is to picture SECDED as binary spellcheck: single typos auto-fixed by position lookup, double typos flagged for panic—keeping server spreadsheets pristine while consumer RAM plays cosmic ray roulette.