Fault-tolerant and redundant systems are both designed to enhance the reliability and availability of critical systems by mitigating the impact of failures. However, there are differences in their approaches and implementations:

1. Fault-Tolerant Systems:

   • Definition: Fault-tolerant systems are designed to continue operating without interruption or degradation in performance, even in the presence of faults or failures.
   • Approach: Fault tolerance is achieved through built-in redundancy and error detection mechanisms that allow the system to detect and recover from faults automatically.
   • Key Features:
     • Redundant components: Fault-tolerant systems often incorporate redundant hardware components (e.g., processors, memory modules, power supplies) that operate in parallel.
     • Error detection and correction: Fault-tolerant systems use techniques such as error checking and correction (ECC), checksums, and parity checking to detect and correct errors in data and computation.
     • Hot-swappable components: Some fault-tolerant systems support hot-swappable components, allowing failed components to be replaced without shutting down the system.
   • Example: A fault-tolerant server with redundant power supplies, processors, and memory modules that can continue running without interruption even if one or more components fail.

2. Redundant Systems:

   • Definition: Redundant systems employ duplicate or backup components or subsystems to provide continuous operation in case of failures.
   • Approach: Redundancy is used to ensure that if one component or subsystem fails, another redundant component or subsystem can take over seamlessly without affecting system operation.
   • Key Features:
     • Standby components: Redundant systems typically have standby or backup components that are activated automatically or manually when a failure occurs.
     • Switchover mechanisms: Redundant systems use switchover mechanisms (e.g., failover, switchover, reconfiguration) to transition from the failed component to the redundant component smoothly.
     • Higher availability: Redundant systems aim to achieve higher availability by minimizing downtime and disruptions caused by component failures.
   • Example: A redundant power supply configuration in a data center where multiple power supplies are connected to a server, and if one power supply fails, another one automatically takes over to ensure continuous power delivery.

In summary, fault-tolerant systems focus on maintaining continuous operation and performance despite the occurrence of faults or failures by incorporating redundancy and error detection/correction mechanisms. Redundant systems, on the other hand, rely on duplicate or backup components to provide seamless switchover and ensure continuous operation in the event of failures. Both approaches aim to improve system reliability and availability, but they differ in their implementation and emphasis on fault detection versus fault recovery.