Your Mac, is running at OS X Mojave, High Sierra, EI Capitan, Yosemite, Mavericks and facing problem on not saving data for volume control level, Screen resolution, Disk selection and useful information those should be stored in memory when your Mac(MacBook Pro, MacBook Retina, iMac, iMac Pro) not on plugged with power or Shutdown. Apple store all the setting and data those set by device owner and not should be changed when it will come to work. Here I explained about NVRAM (non-volatile random-access memory) & PRAM (Parameter RAM), in which case you should reset and how to do.
Note: Data Storage way in NVRAM, setting, and options might be different depending on which Mac model you have. But you can reset NVRAM on Mac OS X using below given steps.
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In which case you need to Reset NVRAM memory and the whole setting
> Speaker volume not saved
> Disk selection should be changed on each startup
> Kernel Panic information not be saved
Step to reset NVRAM on Mac OS X: MacBook Pro, MacBook Retina, iMac and other
In this process, you need to use shortcuts for NVRAM setting reset or PRAM resetting.
Step 1: Put your Mac Shutdown, Go to “Apple Logo” > “Shut Down“.
Step 3: Turn it on, “Use Power Button” to “start your Mac”.
Step 4: Before to hear the startup sound on your Mac device, Press and hold “Command + Option + P + R”.
Note: Windows Keyboard on Mac users can use this keyboard Shortcuts: “Alt + Windows + P + R“.
Step 5: Wait for restart your device automatically, continuously hold keys and release all the keys after listen startup sound on second-time release all the keys.
In the whole process, your Mac restarts two times.
Now you erased all the data stores in NVRAM memory as a Speaker Volume, Screen Resolution, Startup disk selection, and Time Zone information.
Note: Reset NVRAM might resolve Wifi connectivity issue after update your OS X.
→ Using the Same steps you can also “Reset PRAM” (Parameter RAM) on Mac.
reset NVRAM Not Working? What to Do?
If Startup Sound not playing or Keyboard Shortcuts for Reset NVRM or PRAM Won’t responding. Try to follow these tips,
if your Mac Using “Firmware password“, Then these key doesn’t work. Turn Off Firmware password from MacOS Recovery, To Reset NVRAM on Mac, MacBook Pro, MacBook Air.
For Safari: Cookies Settings, Reset safari on Mac and PC
Now you need to reconfigure all the setting erased by this process likes speaker volume, screen resolution, Start-up disk, and your Time Zone selection.
If you are not a success on Reset NVRAM on Mac OS X devices iMac, iMac Pro, Mac Mini, MacBook Pro, Air and other, then you feel free to contact on-line apple support.