Layer 4 — Servers, racks & integration

Position in the die→grid hierarchy: the rack.

The server and the rack it lives in: rack-scale systems and their ODMs, GPU baseboards and trays, the high-layer-count PCBs, connectors, VRMs and passives on every board, plus power shelves, busbars, PDUs and the sheet metal that holds it together.

Parts in this layer

• 4.01 Rack-scale systems (NVL72-class, MI400 Helios-class) · 23 companies
  A rack-scale system is the fully integrated cabinet of compute trays, switch trays, power shelves, cooling manifolds and busbar that ships as one wired unit rather than as discrete servers.
• 4.02 EMS, system integration & rack-level test · 14 companies
  Electronics manufacturing services firms assemble, wire and burn-in the finished server or rack before it ships, standing between the ODM board build and the customer's data center floor.
• 4.03 GPU baseboards & compute trays (HGX, Bianca, UBB/OAM) · 8 companies
  The baseboard is the printed circuit assembly that carries the GPUs (and often paired CPUs) and their direct power and interconnect, packaged into a tray that slides into the rack.
• 4.04 Motherboards, CPU trays, switch trays · 5 companies
  The non-GPU trays in a rack — CPU-only compute trays, host motherboards and the switch trays carrying scale-up switch silicon — built by the same board makers as the GPU trays.
• 4.05 High-layer-count PCBs (HDI, backdrilled, 20–40 layers) · 15 companies
  The bare printed circuit boards themselves — high-density interconnect, backdrilled, 20 to 40 copper layers — that GPU and switch trays are built on.
• 4.06 Copper-clad laminate & PCB materials · 14 companies
  The laminate — resin, copper foil and glass-cloth reinforcement — that high-layer-count boards (4.05) are fabricated from.
• 4.07 Board-level connectors & sockets · 15 companies
  The physical connectors — CPU and GPU sockets, board-to-board and cable connectors, and I/O cages — that link chips, trays and cables together on and between boards.
• 4.08 Board-level power: VRMs, power stages, PoL, power semis · 17 companies
  The voltage regulator modules and point-of-load converters that step rack-level DC power down to the precise, high-current voltages each GPU and chip needs at the board.
• 4.09 Passives (MLCC, inductors, polymer/tantalum, resistors)tight · 12 companies
  The multilayer ceramic capacitors, inductors and other passive components that filter and stabilize power everywhere on a board, populated in far greater numbers on AI boards than on standard servers.
• 4.10 BMC & platform firmware · 6 companies
  The baseboard management controller chip and its firmware, which independently monitor power, temperature and health on a server board and let it be managed remotely, separate from the host CPU or GPU.
• 4.11 Timing, security & misc board silicon · 7 companies
  Clock and timing chips, TPM security modules, and boot flash — the smaller fixed-function silicon that supports the CPU, GPU and BMC on every board without doing the compute itself.
• 4.12 Power shelves & PSUs (33 kW-class ORV3 shelves, rack-level) · 17 companies
  The rack-mounted power shelves that convert facility AC or DC input into the regulated rail distributed to trays across the rack, built to the Open Rack V3 33 kW-class spec used in rack-scale AI systems.
• 4.13 Fans (air-cooled servers, hybrid trays) · 8 companies
  The axial and centrifugal fans mounted in server chassis and rack trays that move air across heatsinks and boards, still needed even in racks that use liquid cooling for the highest-power chips.
• 4.14 Chassis, rails, rack enclosures · 13 companies
  The sheet-metal chassis and mounting rails that trays slide into, and the enclosure (the rack cabinet itself) that houses the whole assembly.
• 4.15 In-rack busbar & power whips · 6 companies
  The high-current busbar and cabling that carries power from the rack's power shelves to each tray, including Nvidia's specified ±48 V / 1,400 A busbar used in rack-scale liquid-cooled systems.
• 4.16 Rack PDUs · 9 companies
  The power distribution units mounted in or beside a rack that meter and distribute power to individual devices, sitting between facility power and the rack's internal busbar or whips.
• 4.17 Air-cooled heatsinks & vapor chambers · 9 companies
  The finned aluminum or copper heatsinks and vapor chambers that spread and dissipate heat from chips that rely on airflow (4.13) rather than a liquid cold plate.

Public plays in this layer

Listed companies with the most part placements in layer 4. Placement count is breadth, not revenue exposure.