---
id: multi-unit-stacking
title: "Multi-Unit Stacking"
status: provisional
source_sections: "Web research: WCCFTech, NVIDIA newsroom"
related_topics: [connectivity, gb10-superchip, ai-workloads, memory-and-storage]
key_equations: []
key_terms: [connectx-7, smartnic, qsfp, stacking, nvlink]
images: []
examples: []
open_questions:
  - "Exact cable/interconnect required between units (QSFP type, length limits)"
  - "Software configuration steps for multi-unit mode"
  - "Performance overhead of inter-unit communication vs. single unit"
  - "Does stacking appear as a single device to frameworks or require explicit multi-node code?"
  - "Can more than 2 units be stacked?"
---

# Multi-Unit Stacking

Two Dell Pro Max GB10 units can be connected together to create a more powerful combined system, effectively doubling the available compute and memory.

## 1. How It Works

Each Dell Pro Max GB10 has **2x QSFP 200 Gbps ports** powered by the NVIDIA ConnectX-7 SmartNIC. These ports enable direct unit-to-unit connection:

- **Combined memory:** 256 GB unified (128 GB per unit)
- **Combined compute:** 2 PFLOP FP4 (1 PFLOP per unit)
- **Interconnect bandwidth:** Up to 400 Gbps (2x 200 Gbps QSFP)

## 2. Model Capacity

| Configuration  | Memory  | Max Model Size (approx) |
|---------------|---------|-------------------------|
| Single unit    | 128 GB  | ~200B parameters (FP4)  |
| Dual stacked   | 256 GB  | ~400B parameters (FP4)  |

This enables running models like **Llama 3.1 405B** (with quantization) that would not fit in a single unit's memory.

## 3. Physical Configuration

The compact form factor (150x150x51mm per unit) is designed to be **stackable** — two units can sit on top of each other on a desk, connected via short QSFP cables.

## 4. Open Areas

This feature is one of the less-documented aspects of the system. Key unknowns include the exact software configuration, whether it presents as a single logical device, and inter-node communication overhead. See open questions in frontmatter.

## Key Relationships

- Connected via: [[connectivity]] (QSFP/ConnectX-7 ports)
- Extends capacity of: [[ai-workloads]]
- Doubles resources from: [[gb10-superchip]], [[memory-and-storage]]