RAM, FP-ROM, and RTOS in Brocade switches

Back to: Brocade FC (Fibre Channel) Switches

explanation of RAM, FP-ROM, and RTOS in Brocade switches:

1. RAM (SD-RAM) in Brocade Switches:

• Purpose: RAM (specifically SD-RAM) is used as temporary memory to store data being actively processed by the switch’s ASIC (Application-Specific Integrated Circuit).
• Capacities: Depending on the switch’s speed and processing requirements, RAM capacities vary:
  • 32 MB
  • 64 MB
  • 128 MB
  • 256 MB
    …and higher in modern switches.
• Higher-speed switches require more RAM to handle increased workloads and faster data throughput.

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2. FP-ROM (Flash Programmable Read-Only Memory):

• Role: FP-ROM in Brocade switches acts like a hard disk in regular computers—it stores the switch’s firmware, bootloader, and essential software (like the RTOS and Fabric OS).
• Capacities: Early FP-ROM chips had lower capacities due to high flash memory costs, but as prices fell, switches started using larger-capacity chips:
  • 32 MB
  • 64 MB
  • 128 MB
  • 256 MB
    …and expandable based on functional requirements.
• Importance: FP-ROM is crucial—it’s the heart of the switch—because it holds the embedded system software needed for the switch’s core functions. Without FP-ROM, the switch cannot boot or operate.

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3. Real-Time Operating System (RTOS) in Brocade Switches:

• An RTOS is more powerful than a traditional OS because it provides predictable, real-time responses essential for high-performance networking tasks.
• The RTOS contains:
  • Kernel — the core component managing system resources and task scheduling.
  • Device Drivers — interfaces to hardware components (ASIC, ports, etc.).
  • Modules — additional components loaded dynamically for extra functionality.

RTOS Evolution in Brocade:

1. VXWORKS (Pre-Bloom II switches):
   • Lightweight, reliable RTOS known for stability—it never crashes.
   • Very small footprint (thin size), ideal for older FP-ROM with limited capacity.
   • Device drivers were stored in binary format.
2. Linux RTOS (From Bloom II switches onward):
   • More advanced and feature-rich compared to VXWORKS.
   • Larger footprint (thicker size) due to added functionalities.
   • Device drivers are stored in RPM format (Red Hat Package Manager).
   • Used as FP-ROM sizes increased, allowing for larger, more complex OS versions.