Apple iMac Retina 4k, Late 2015, 21.5 Quick Start Guide
![Apple iMac Retina 4k, Late 2015, 21.5 manual cover](/images/9b01fd51f1e4d3e738503103/thumbs/thumb175x175.webp)
To reset the NVRAM, shut down your iMac. Turn it on and immediately press and hold Option, Command, P, and R keys for about 20 seconds. The computer might restart during this process.
First, check the power connection and ensure the power cable is secure. Try a different power outlet. If it still doesn't turn on, reset the SMC by unplugging the power cord, waiting 15 seconds, and then plugging it back in.
Unfortunately, the RAM on the iMac Retina 4K, Late 2015 model is not user-upgradable as it is soldered onto the motherboard. Consider external memory solutions if more memory is needed.
Check for software updates and install them. Clear unnecessary files and applications. Consider upgrading to a faster SSD if you have an HDD. Running Activity Monitor can help identify apps consuming excessive resources.
Back up your data first. Restart your iMac and hold Command + R to enter Recovery Mode. Select 'Disk Utility' to erase your drive. Then, choose 'Reinstall macOS' from the utilities window.
The iMac Retina 4K, Late 2015 supports one external display with up to 4096x2304 resolution at 60Hz, connected via Thunderbolt 2 or HDMI (with an adapter).
Click on the Wi-Fi icon in the top-right corner of your screen. Select your network from the dropdown menu and enter the password if required.
No, the iMac Retina 4K, Late 2015 does not support Target Display Mode. This feature is only available on older iMac models.
Click on the Apple menu and select 'About This Mac'. Then, go to the 'Storage' tab to view the capacity and available space on your iMac's storage drive.
Keep your iMac clean by dusting regularly. Ensure software is up-to-date. Monitor system performance and clear unnecessary files. Use a surge protector to prevent electrical damage.