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Email: kwkimbest@gmail.com

I write under the pen name wafernote. Everything published here is independent, personal analysis based on public sources.

Corrections: If you find a factual error, please email me with the post URL and the source. Corrections are added at the bottom of the post with the date.

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Why Nvidia's Inference GPU Skips HBM for GDDR7

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  "More inference means more HBM demand" is a common shorthand. Nvidia's own inference-only GPU says otherwise: Rubin CPX, unveiled September 9, 2025, carries no HBM at all. It runs on 128GB of GDDR7 — the same memory family used in gaming graphics cards. KEY TAKEAWAYS 1. Rubin CPX, Nvidia's inference-specialized GPU announced Sep 9, 2025, uses 128GB of GDDR7 instead of HBM4. Shipments are planned for late 2026. 2. Its estimated memory bandwidth is roughly 2.1TB/s — about 1/10th of Rubin's 22TB/s HBM4 bandwidth. That's a design choice, not a shortfall: the workload it targets needs less memory bandwidth. 3. Nvidia splits inference into two stages — prefill and decode — and now builds separate chips for each. Prefill runs on Rubin CPX; decode runs on HBM4-equipped Rubin. Estimated memory bandwidth by chip. Rubin CPX figure is back-calculated from rack-level totals, not a disclosed per-chip spec. What Rubin CPX actually is Nvidia describes Rubin CPX as a new cla...
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Korea's August Chip Exports Hit a Record $46.7B. Volume Moved Too

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  Korea's semiconductor exports reached $46.65 billion in August, up 209.0% from a year earlier and 13.8% above July, according to the Ministry of Trade, Industry and Energy's August trade report released September 1. It is a new all-time monthly high, taking out June's $44.81 billion after a one-month dip. The number everyone will quote is the 209%. The number I think matters more is the 13.8%, because contract prices for commodity memory rose only 1% to 4% in August. For the first time this cycle, volume and mix did most of the month-on-month work. KEY TAKEAWAYS 1. Chip exports hit a record $46.65 billion in August (+209.0% YoY, +13.8% MoM) and now make up 47.5% of all Korean exports, versus 25.9% a year ago. 2. August's month-on-month gain outran price. DDR4 8Gb contract prices rose 4.2%, DDR5 16Gb 3.3%, NAND 128Gb 1.4%. An implied volume/mix index (Jan = 100) moved from 96 in July to 105 in August. 3. The growth is memory, not logic. Memory chips were $40.94 billion...
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DDR4 Costs More Than DDR5 — Unless You're Actually Buying It

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  You have probably seen the headline: legacy DDR4 now costs more than newer DDR5 . Then you open a price comparison site to actually buy a stick, and the tags are the other way round. DDR5 is far more expensive. Both numbers are real. They are just measuring different things , and the distance between them says something about how strange this memory market has become. KEY TAKEAWAYS 1. On July 1, 2026, spot quotes put a DDR4 16Gb die at $74.63 against $46.83 for DDR5 16Gb — DDR4 59% higher . 2. That same month, Korean retail averaged about $151 for a DDR4 16GB module and $244 for a DDR5 16GB module — DDR5 61% higher . 3. Different units (one die vs one module) and different markets (spot vs retail). The two figures cannot be converted into each other , and reporting that treats a "16Gb" quote as a module price is off by a factor of eight. Same month. Opposite conclusions. Two numbers, both true Start with the chip. On DRAMeXchange spot on July 1, 2026 , the DDR4 16Gb...
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