How DRAM changed the world

Original Article ↗ Hacker News Discussion ↗

Advances in DRAM are increasingly constrained by physical limits on capacitor size, refresh behavior, and latency, leading to slower cost and performance improvements compared to the rapid gains seen in the 1990s and early 2000s. Commenters contrast DRAM with SRAM—denser but slower-to-evolve versus faster and more power-hungry—and explore why large SRAM-based main memory or user-addressable “SRAM tiers” have not become mainstream despite potential speed benefits. Alongside technical details like fixed ~15 ns DRAM latencies and row-refresh mechanics, the conversation reflects nostalgia for past eras of transformative RAM upgrades and touches on how modern workloads, SSDs, and high-resolution video (4K/8K) change what “more and faster memory” practically delivers today.

DRAM Scaling Limits and Economics

  • Several comments argue DRAM scaling has effectively stalled: stuck near “10 nm” classes, with very slow cost/GB improvements over the last ~15 years.
  • One view: DRAM cell capacitors hit a practical speed limit around 400 MHz and a charge limit of tens of thousands of electrons, making further shrinking and faster access extremely hard.
  • Another thread disputes “flat prices,” citing DRAM dropping from ~$10/GB (2009) to around $1–2/GB recently, but agrees the price curve has flattened relative to the 1990s–2000s.

SRAM as DRAM Replacement / Large Caches

  • Idea raised: once advanced nodes (e.g., 5 nm) are cheaper, put ~GB of SRAM on-die as an L4 cache and potentially replace DRAM.
  • Pushback: SRAM is many times more expensive per bit, uses more power, and very large dies face latency limits from signal propagation and energy cost of data movement.
  • Some suggest partial solutions (e.g., hundreds of MB of SRAM alongside DRAM), but others question market demand and note that hardware-managed caches already serve this role.
  • Historical hybrid designs (e.g., DRAM with embedded SRAM cache) existed but saw little adoption.

DRAM Operation, Refresh, and Reliability

  • Discussion contrasts DRAM vs SRAM: DRAM stores each bit in a transistor+capacitor cell that must be periodically refreshed; SRAM uses multi-transistor flip-flops that hold state without refresh at typical system timescales but at much higher area and power.
  • Reading DRAM is “destructive”: entire rows are sensed into SRAM-like buffers and then written back, so refresh can be implemented by periodic row reads.
  • Early systems sometimes needed explicit software refresh loops; later, controllers automated it.
  • Reduced margins and infrequent refresh lead to phenomena like rowhammer; some commenters call all modern DDR3/4 “defective by design” from a correctness standpoint.

Debate on Memory Latency Across DDR Generations

  • One line claims DRAM latency has been roughly stuck around ~13–17 ns since early DDR, limited by capacitor physics.
  • Others note specific modules (e.g., fast DDR2, DDR4, DDR5) achieving ~7.5–10 ns “first data” latency, arguing there has been some progress, though acknowledged as modest.
  • Consensus: bandwidth has risen dramatically; latency improvements are small and often offset by higher CAS timings.

User Experience and Nostalgia Around RAM

  • Many reminisce about transformative 1990s upgrades (e.g., 4→16 MB, 8→32 MB), which eliminated swapping and enabled new software classes.
  • In contrast, 8→32 GB today is seen as incremental for typical use (more tabs, VMs) rather than life-changing, partly because SSDs have narrowed the penalty of not fitting entirely in RAM.
  • Stories highlight past RAM cost (SIMM prices rivaling CPUs), elaborate upgrade hacks, and how rapid hardware progress then contrasts with today’s long-lived machines.

8K Video and High-Resolution Capture

  • Skepticism: for casual users, 4K and especially 8K impose heavy storage/battery costs with limited visible benefit on typical screens and streams.
  • Supporters point to professional and niche uses:
    • Post-production flexibility (crop, reframe, stabilize while still outputting 4K).
    • VR video, where 8K+ is described as clearly better than 4K.
    • Scientific/industrial imaging (e.g., mineral studies under high magnification).
  • Some emphasize that streaming services often under-deliver bitrate, so “4K” streams can look worse than high-bitrate 1080p; local playback can better exploit high resolution.