PEX8796-AB80BI: Technical Guide to Broadcom's 96-Lane PCIe Gen3 Switch

Introduction

The PEX8796-AB80BI is a high-performance 96-lane PCI Express Gen3 switch manufactured by Broadcom (formerly PLX/Avago), providing 24-port configurable PCIe switching fabric with non-transparent bridging, multicast, and advanced traffic management for enterprise servers, storage systems, GPU computing, and high-bandwidth data center applications requiring scalable PCIe connectivity.

This enterprise-class switch supports up to 96 lanes of PCIe Gen3 (8 GT/s per lane) with flexible port configurations (x1, x2, x4, x8, x16) across 24 ports, delivering up to 192 GB/s aggregate bandwidth for connecting CPUs, GPUs, NVMe SSDs, network adapters, and accelerators in complex multi-host server architectures.

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Technical Overview

Core Specifications

Parameter	Specification
PCIe Generation	Gen3 (8.0 GT/s)
Total Lanes	96 lanes
Ports	24 configurable ports
Port Widths	x1, x2, x4, x8, x16
Aggregate Bandwidth	192 GB/s (bidirectional)
Non-Transparent Bridging	Supported
Multicast	Hardware multicast support
Package	FCBGA
Power	~15-20W typical

Key Features

Massive Lane Count:

• 96 PCIe Gen3 lanes
• 24 flexible ports
• Any lane-width combination (x1 to x16)
• Non-blocking switching fabric

Advanced Features:

• Non-Transparent Bridging (NTB): Isolate host domains
• Multicast: Efficient one-to-many data distribution
• Quality of Service (QoS): Traffic prioritization
• Hot-plug support: Dynamic device insertion/removal
• SRIS (Separate Reference Independent Spread Spectrum): Simplifies clocking

Enterprise Capabilities:

• Advanced Error Reporting (AER)
• End-to-End CRC protection
• Failover and redundancy support
• Low-latency cut-through switching
• Programmable via I²C/SMBus

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Complete Specifications

Performance Specifications

Parameter	Value
Data Rate per Lane	8.0 GT/s (Gen3)
Per-Lane Bandwidth	1 GB/s (8 Gbps, 8b/10b encoded)
Maximum Throughput	96 GB/s per direction (192 GB/s total)
Latency	<1 μs (cut-through)
Packet Size	Up to 4KB TLP (Transaction Layer Packet)

Port Configuration Flexibility

Example Configurations:

• 6× x16 ports (96 lanes total)
• 12× x8 ports (96 lanes total)
• 24× x4 ports (96 lanes total)
• Mixed: 4× x16 + 8× x4 (96 lanes)

Typical Usage:

• Upstream: 1× x16 to CPU
• Downstream: 4× x16 GPUs + 8× x4 NVMe SSDs

Electrical Specifications

Parameter	Value
Supply Voltage	1.0V (core), 3.3V (I/O)
Power Consumption	15-20W typical (configuration dependent)
PCIe Compliance	PCI-SIG Gen3 certified

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Applications

GPU Computing Servers

AI/ML Training Clusters:

CPU (Root Complex)
    ↓ x16
PEX8796-AB80BI
    ├─► GPU 1 (x16) - NVIDIA A100/H100
    ├─► GPU 2 (x16) - Deep learning
    ├─► GPU 3 (x16) - Training workloads
    ├─► GPU 4 (x16) - Model inference
    └─► NVMe SSD array (4× x4) - Dataset storage

Enables multi-GPU configurations
Peer-to-peer GPU communication via switch
Direct GPU-to-GPU data transfer

NVMe Storage Arrays

All-Flash Arrays:

• 24× NVMe SSDs (x4 each = 96 lanes)
• Aggregate: 96 GB/s bandwidth
• Low-latency direct-attached storage
• Enterprise storage controllers

Advantages:

• Massively parallel storage access
• Eliminates SAS/SATA bottlenecks
• Sub-microsecond latency switching

Multi-Host Servers

Non-Transparent Bridging (NTB):

Host 1 (CPU A) ◄──┐
                  │
            PEX8796-AB80BI (NTB mode)
                  │
Host 2 (CPU B) ◄──┘

Shared PCIe devices:
- Shared NVMe storage
- Shared GPUs
- Shared network adapters

Each host sees isolated address space
NTB provides inter-host communication

High-Frequency Trading (HFT)

Ultra-Low Latency:

• FPGA accelerator cards
• Market data feed NICs
• Trading algorithm processors
• <1 μs switching latency critical

Video Production / Broadcast

Real-Time Video Processing:

• Multiple GPU render nodes
• High-speed video capture cards
• NVMe scratch storage
• 4K/8K video workflows

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Design Considerations

Thermal Management

Power Dissipation:

• Typical: 15-20W
• Maximum: ~25W (full utilization)

Cooling Requirements:

• Heatsink mandatory (forced air)
• Thermal pad to chassis/cold plate
• Maintain junction <100°C

PCB Design

Critical Requirements:

Differential Pairs:

• 100Ω differential impedance
• Matched lengths within ±5 mils per lane
• Minimize vias and discontinuities

Signal Integrity:

• Gen3 (8 GT/s) requires careful routing
• Use low-loss PCB materials (e.g., Megtron 6)
• Minimize crosstalk between lanes

Power Delivery:

• Clean 1.0V and 3.3V rails
• Multiple decoupling capacitors
• Low-ESR bulk capacitors

Clocking

SRIS Support:

• No common reference clock required
• Simplifies multi-card designs
• Independent clock domains per port

Clock Sources:

• 100 MHz differential reference clock
• Spread spectrum compatible

Software Configuration

Programming:

• I²C/SMBus interface for configuration
• Port bifurcation settings
• NTB domain assignments
• Traffic shaping parameters

Operating System Support:

• Linux: Native PCIe enumeration
• Windows Server: Full driver support
• VMware ESXi: PCIe passthrough capable

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Conclusion

The PEX8796-AB80BI delivers enterprise-class 96-lane PCIe Gen3 switching with 24 configurable ports, 192 GB/s aggregate bandwidth, and advanced features including non-transparent bridging and hardware multicast. Ideal for GPU computing, NVMe storage arrays, multi-host servers, and high-performance data center applications requiring massive PCIe connectivity with sub-microsecond latency.

Key Advantages:

✅ 96 Lanes: Massive PCIe Gen3 connectivity
✅ 24 Ports: Flexible x1-x16 configurations
✅ 192 GB/s: Non-blocking aggregate bandwidth
✅ NTB Support: Multi-host isolation and sharing
✅ Low Latency: <1 μs cut-through switching
✅ Enterprise-Grade: AER, hot-plug, failover support

Designing high-performance servers? Visit AiChipLink.com for technical resources and PCIe architecture consultation.

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Written by Jack Elliott from AIChipLink.

 

AIChipLink, one of the fastest-growing global independent electronic   components distributors in the world, offers millions of products from thousands of manufacturers, and many of our in-stock parts is available to ship same day.

 

We mainly source and distribute integrated circuit (IC) products of brands such as Broadcom, Microchip, Texas Instruments, Infineon, NXP, Analog Devices, Qualcomm, Intel, etc., which are widely used in communication & network, telecom, industrial control, new energy and automotive electronics. 

 

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