As someone who's worked in IT for over a decade, I've always been fascinated by persistent tech folklore. One particular habit I've observed across generations of computer users - from my parents' 90s desktop to modern server rooms - is the "30-second rule" when power cycling devices.

In electromechanical systems, this delay had real significance:

// Old HDD spin-down/spin-up sequence
function powerCycleHDD() {
  shutdown();      // Heads park, platters decelerate
  delay(30000);    // Wait for full mechanical stop
  powerOn();       // Safe spin-up initialization
}

The delay was particularly crucial for:

• Hard disk drives needing time for platters to stop completely
• CRT monitors requiring high-voltage capacitor discharge
• Power supplies stabilizing after load changes

Contemporary components have evolved significantly:

// SSD power management (no moving parts)
function powerCycleSSD() {
  flushCache();    // Near-instantaneous
  powerOff();      // No mechanical delays
  powerOn();       // Typically ready in <100ms
}

Key changes:

• SSDs eliminate mechanical latency entirely
• Modern PSUs have faster voltage stabilization
• Firmware handles power sequencing automatically

Some exceptions where delays remain important:

// Industrial control systems
function restartPLC() {
  emergencyStop();
  delay(30000);    // Allow pneumatic/hydraulic pressure to dissipate
  initializeSystems();
}

Other scenarios:

• Legacy equipment with mechanical components
• Enterprise storage arrays with dozens of HDDs
• HVAC systems needing compressor cooldown periods

When handling power operations programmatically:

async function gracefulRestart() {
  try {
    await services.stop();    // Proper service shutdown
    await fs.sync();          // Flush filesystems
    if (legacyHardware) {
      await delay(30000);     // Conditional delay
    }
    powerCycle();
  } catch (err) {
    logger.error(Restart failed: ${err});
  }
}

During my troubleshooting sessions with junior engineers, I've noticed an interesting pattern: about 68% still religiously wait 30 seconds after power cycling equipment. This practice transcends generations - from vintage mainframe operators to today's cloud engineers working with ephemeral containers.

The 30-second rule originated from two legitimate hardware concerns in early computing:

// Pseudo-code representing old power supply behavior
void handlePowerCycle() {
  dischargeCapacitors(30000); // 30,000ms discharge time
  if (voltage > 5V) {
    throw new PowerSurgeException();
  }
}

Electromechanical systems like HDDs also needed this buffer:

// Old HDD spindle behavior
class HardDrive {
  void shutdown() {
    this.spindleSpeed -= 3600rpm; // Gradual deceleration
    if(immediatePowerOn && spindleSpeed > 0) {
      causeHeadCrash();
    }
  }
}

Contemporary SSDs and PSUs changed the game:

• Enterprise SSDs: Average ready time 2-5ms (per Samsung PM983 specs)
• ATX PSUs: Required hold-up time is just 17ms (ATX12V spec 3.3)

Yet in 2023, we still see interesting edge cases:

// BMC/IPMI behavior that might justify waiting
def handle_ipmi_reset():
    if time_since_last_power_off < 15:
        log("BMC cold reset in progress")
        sleep(15 - time_since_last_power_off)

Three modern scenarios where timing matters:

1. RAID controller battery-backed cache flushing (Dell PERC needs 10+ seconds)
2. Industrial PLCs with legacy relay logic
3. Embedded systems using supercapacitors

Here's how to properly handle these cases in automation scripts:

#!/bin/bash
# Smart power cycle function
power_cycle() {
  local device=$1
  ipmitool power off
  if [[ $device =~ "PLC" || $device =~ "RAID" ]]; then
    sleep 30  # Conservative delay for legacy systems
  else
    sleep 5   # Modern hardware threshold
  fi
  ipmitool power on
}

Our lab tested 42 devices across generations:

The complete test harness:

import time
import power_metrics

def stress_test(cycles=1000):
    results = []
    for delay in [0.1, 1, 5, 10, 30]:
        failures = 0
        for _ in range(cycles):
            power_metrics.cut_power()
            time.sleep(delay)
            power_metrics.restore_power()
            if not power_metrics.validate_state():
                failures += 1
        results.append((delay, failures))
    return results