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Hot Chips 2026: Samsung makes LPDDR5X smart with logic unit in memory — LPDDR5X-PIM is 3.01x faster than LPDDR5X in AI inference with 8x the bandwidth
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Earlier this month, Samsung introduced the industry's first LPDDR5X-PIM memory, adding in-memory logic to the low-power memory standard, and at Hot Chips 2026, it dove into the memory technology that's we've previously seen at play through HBM stacks.
PIM, or Processing-in-Memory, is a technology Samsung demoed as early as 2021, piloted through HBM stacks in AMD accelerators. It's a small bit of logic that sits alongside DRAM cells, allowing basic calculations to happen directly in-memory. By handling those basic calculations locally, Samsung is able to eliminate the processor as a bottleneck and speed up, in particular, AI inference. In inference tasks, Samsung says its LPDDR5X-PIM is 2.28x faster than standard LPDDR5X, in fact.
The reason for adding in-memory processing to LPDDR5X is pretty clear: HBM is too damn expensive. Micron warned just a day earning at Hot Chips that the HBM wafer demand is only getting worse, and Samsung opened its presentation with something we're all well aware of. Memory makes up the bulk of AI chip costs, and its share of the pie continues to grow. Add on top of that the power demands of DDR5, much less HBM, and LPDDR5X seems like an ideal target for PIM.
Samsung introduced HBM-PIM in 2023, and at the time, introduced the concept of LPDDR5X-PIM. What it shared at Hot Chips is a real product, taking the concept of LPDDR5X-PIM and putting it through validation. Samsung is also looking ahead for LPDDR6X-PIM, and the company says it hopes to have an initial specification from JEDEC this year.
Above, you can see a basic layout of how Samsung integrated PIM into LPDDR5X. Each memory bank has its own PIM, which is an advancement over HBM-PIM, where Samsung had to cut banks to fit the logic. The memory bank, scale register file, and source register file feed parallel MAC trees. Once calculated, the output (either integer or floating point output) is written to a vector register file.
Samsung says its LPDDR5X can operate in two modes: single-bank (traditional DRAM) or multi-bank (PIM). Traditional DRAM controllers work, with commands switching between standard read/write or a PIM read/write depending on the mode. The challenge, according to Samsung, was reordering with conventional DRAM.
Samsung uses what it calls Address Align Mode (AAM) to get around the reordering issue. It maps DRAM addresses to MAC instructions, assigning the VRF/SRF address based on the RA/CA address, respectively, and not the Instruction Register File.
To demonstrate how data moves through the memory cells and calculations are performed, Samsung provided an example of a MAC operation, assuming weight parameters for the data are already written into the cell, and the memory is operating in multi-bank (PIM) mode.
Storing 512 bytes of FP8 activation data, it's first broken down into 16, 256-bit packets, which are written into each of the banks in and noted in the Source Register File.