DDR vs. LPDDR Wiki

Quick definition

DDR (Double Data Rate SDRAM): Mainstream dynamic memory for desktops, workstations, and servers. Uses pluggable modules (DIMMs/SO-DIMMs), wide channels, high capacities, and motherboard-friendly signaling.
LPDDR (Low-Power DDR): DRAM family optimized for mobile, embedded, and thin/edge devices. Uses much lower I/O voltages, aggressive power states, and compact packages (often stacked on the SoC).

DDR: Maximize capacity and sustained bandwidth per socket, support field upgrades/replacements, scale to multi-socket systems, and tolerate longer board traces and connectors.
LPDDR: Minimize energy per bit and idle power, enable tight thermals and small footprints, and deliver enough bandwidth for highly parallel SoCs (CPU/GPU/NPU/ISP) within a battery budget.

I/O voltage: LPDDR generations drop VDDQ much lower than DDR peers → big I/O power savings.
Topology:
- DDR: DIMM slots with edge connectors; fly-by command/address; termination schemes sized for longer channels.
- LPDDR: Short, point-to-point routing (often Package-on-Package above the SoC) with minimal trace length and lower swing signaling.
Upgradability:
- DDR: Replaceable modules (UDIMM/SO-DIMM/RDIMM/LRDIMM/CUDIMM).
- LPDDR: Soldered BGA or PoP → not field-upgradeable.
Channel width:
- DDR: Typically 64-bit data per channel (72-bit with ECC).
- LPDDR: Multi-channel narrow interfaces (e.g., LPDDR4/5 devices expose two ×16 channels; LPDDR6: two ×12 sub-channels with explicit metadata handling).

DDR4: up to ~3200 MT/s per pin
DDR5: baseline 4800 MT/s, scaling to ~7200–8800+ MT/s (vendor/grade dependent)
LPDDR4/4X: ~3200–4266 MT/s
LPDDR5/5X: ~6400–8533 MT/s
LPDDR6: ~10,667–14,400 MT/s per pin (next-gen mobile/edge)

Effective bandwidth depends on channel count, ranks/banks, controller policy, and thermals.

Raw CAS timings (in cycles) are often higher for LPDDR, and deep power states add entry/exit latency.
End-to-end: Modern LPDDR controllers use many narrow channels and smart schedulers to keep tail latency acceptable for camera/display/AI bursts. DDR’s wider channels typically offer lower variance under heavy, long-burst server loads.

LPDDR focuses on energy/bit and idle power:
- Deep/partial self-refresh (PASR), clock stop, retention, DVFS/DVFSL.
- Short PoP interconnects reduce I/O capacitance.
DDR relies more on platform-level cooling and PSU headroom; higher drive strengths and terminations tolerate long traces and sockets but raise I/O power.

DDR5: on-die ECC (ODECC) for cell reliability at very high speeds; server parts add DIMM-level ECC (72-bit data path) and RAS features (scrubbing, chipkill on certain DIMMs).
LPDDR (newer gens): on-die ECC/parity, diagnostics, activation counters/telemetry aimed at automotive/edge longevity; host-visible ECC varies by platform.

DDR: UDIMM/SO-DIMM for clients; RDIMM/LRDIMM/CUDIMM for servers; hot-swap/field service in data centers.
LPDDR: PoP for phones/tablets (DRAM stacked over the SoC), or discrete BGA on laptops/automotive boards when capacity/thermals demand.

DDR5: dual 32-bit sub-channels per DIMM rank, higher bank counts, improved training; module-side PMIC.
LPDDR5/5X/6: dedicated data strobe clocking (WCK for 5/5X), multi-channel arbitration, fine-grained low-power entry/exit, and explicit handling of sub-channels + metadata (LPDDR6).

DDR usually wins cost/GB and max capacity (multiple DIMM slots).
LPDDR often costs more per GB but saves system cost by enabling smaller boards, thinner devices, and smaller batteries for a given runtime.

Choose DDR when: you need field-upgradeable memory, large capacities (e.g., 64–1024+ GB per system), long sustained throughput, or server-class RAS (ECC DIMMs, advanced telemetry).
Choose LPDDR when: you must hit tight power/thermal budgets in mobile, ultra-thin laptops, embedded/edge AI, AR/VR, or automotive ECUs—while still meeting high bandwidth per watt.

Dimension	DDR	LPDDR
Form factor	DIMM/SO-DIMM (socketed)	BGA or PoP (soldered)
Channel width	64-bit (72-bit ECC)	Dual ×16 (LPDDR4/5), 2××12 sub-channels (LPDDR6)
Voltage & I/O	Higher VDDQ; longer traces/connectors	Much lower VDDQ; short routes, low swing
Power features	Self-refresh, power-down; fewer deep states	PASR, DVFS/L, deep idle modes, fast entry/exit
Bandwidth scaling	Wider buses, more DIMMs/ranks	More narrow channels/sub-channels
Capacity	Very high (multi-DIMM)	Moderate (soldered packages)
Serviceability	User-replaceable	Not user-replaceable
Best fit	Desktops, workstations, servers	Mobile, ultra-thin PCs, edge/auto/IoT

DDR is the workhorse for capacity and serviceability in socketed systems.
LPDDR is engineered for efficiency and compactness, delivering impressive bandwidth within strict power and thermal envelopes.
As AI and graphics loads spread from servers to edge devices, LPDDR’s many-channel, battery-first design keeps it the default memory for mobile and embedded systems, while DDR continues to dominate upgradable PCs and data centers.