"Macintosh HD isn't visible in Disk Utility after trying to update OS X"に関する回答Just had this issue myself on a 2012 Mac Mini, which suddenly locked up completely and couldn’t restart. When I rebooted off a USB, the drive had completely disappeared. Time to order a new drive. Fortunately I have performed a hard drive swap as documented in Mac mini Late 2012のハードドライブ交換 several times and have backups of everything, making this merely annoying as opposed to fatal. As a general practice, I always keep my OS and data on several drives, backing up to a third, and have been doing so for decades. I realise this isn’t practical for Macbooks, though.
"iMac 2021 model 27" RAM upgrades"に関する回答The M1 iMac is 24”, not 27”, although the increased screen real estate mitigates that somewhat. It features unified memory (https://www.apple.com/uk/newsroom/2021/0...-features-all-new-design-in-vibrant-colors-m1-chip-and-45k-retina-display/). There is no support for upgrading the integrated memory on an M1 chip whatsoever - it’s exactly the same as the earlier M1 macs (and, for that matter, the Raspberry Pi). I expect some Apple Fanboy will be along to say “but, but, buuuuut unified memory is faster”. Sure, until it fails, then it doesn’t work at all, and you can’t swap it out for another module.
"I get a white screen upon power on."に関する回答Always, always, have a USB boot disk to hand. It makes diagnosing problems much easier. From my experience, a dead hard drive will result in a question mark being displayed on boot. Faulty RAM will involve a black screen and beeps. A failed display will give you the chimes but a black screen. On the logic board, there is an array of LEDs below the display connector, which will light up if the board is operational. The white screen boot problem sounds like a bad graphics card. From my experience, the GPU is the most likely thing to overheat on an iMac. As you cannot easily open the machine, dust accumulates inside it, trapping airflow and eventually leading to overheating failure. Typical symptoms are random lines appearing across the display at all times, and / or booting to a blank screen. However, you can still usually boot to safe mode, even when the display is messed up. If you’re really stuck, you can hold down Control+S on startup and go into single user mode. If that works, your CPU, disk and RAM is...
"Hard Drive and Memory Upgrade"に関する回答The first Mac Minis allowed a CPU upgrade (if you were brave enough) as well as RAM, disk and optical drive. Obviously you could only put in what the motherboard supported, but it was a step in the right direction. Even the 2012 model is okay, I've got mine up to 16GB RAM and two hard drives totalling 1.5TB, the latter using the guides on this very site. For me, the killer decision to not by an M1 Mac Mini, along with the non-upgradable disk and RAM (meaning I cannot buy the base model now and upgrade on the cheap in 6 months) is this : https://discussions.apple.com/thread/252...