Difference between "Restart..." and "Shutdown"/turn-back-on?

Since you asked:

When you select Restart, macOS shuts down all running processes, logs you out, and reloads the operating system. The Mac does not fully cut power to the hardware. Instead, certain components (such as the logic board, some memory caches, and peripheral devices) remain in a low-power state. Temporary files in RAM are cleared, but some firmware and low-level system settings may persist.

When you shut down the Mac, all power to internal components is fully cut off. This forces all hardware components to fully reset, including the SMC (System Management Controller) and PRAM/NVRAM (depending on the Mac you have). When you turn it back on, the Mac goes through a complete hardware initialization process, which can resolve deeper system issues.

>One reason I ask is because I've been told that there are apps that don't behave well if that cold restart doesn't occur.

Unless they're doing something _really_ weird at a hardware level, there's no practical way an application can tell the difference.

Yes, it's true that contents of RAM could still be read for a short while after being unpowered. RAM basically stores a voltage in some medium and that voltage dissipates over time, needing to be constantly refreshed to retain its value.

Waaaay back in the day of solid state memory systems, early systems may have used delay lines or vacuum tubes, with decay times (the time it took for the memory content to decay or get lost if not refreshed) measured in seconds, and leaving the system off for ≈30 seconds or so guaranteed that the voltages would dissipate and wipe the memory (think: give time for a vacuum tube to cool down)

Modern memory systems use semiconductors, transistors or capacitors, with decay times measured in milliseconds, at best, so the whole concept of time is shifted. Human memories are long, by comparison, and we still sometimes live by the 'good old days'.

In addition, modern memory techniques render most such actions around memory recovery moot. After a reboot, the whole memory is basically scrambled, so no data is where you think it was just moments ago.

So no, for all intents and purposes, there's no difference between Restart and Shutdown/wait/power-on as far as everyday computing is concerned, and no application you're running is likely to be able to tell the difference.

FWIW, without going into too much detail, the following is the steps a Mac goes through when booting up from a cold start:

• Phase 1: System Initialization
  • Firmware (aka, Boot ROM) - Tests & initializes the Mac's HW, then locates and starts the Booter.
  • Booter - Loads the macOS Kernel and essential kernel extensions (kexts) into RAM, and then, allows the Kernel to take over. This is when the Apple logo appears on the screen.
  • Kernel - Provides the macOS foundation and loads additional drivers and the core operating system. This is when the Progress Bar appears on the screen.
  • Launchd - Root is the owner of this process and it is the 1st parent process that spawns other child processes. The last step of the launchd process is to display the user login window.
• Phase 2: User Sessions
  • Loginwindow - Runs as a background process. It coordinates with the opendirectoryd process to authenticate the user. Once authenticated, it works with launchd to initialize the graphical user interface. Once that is done, it starts any user login items.

drhender wrote:

A particular vendor's VPN software

Just so you know, VPNs are probably the #1 hottest scam app right now.

I'm sure the problem here is just a bug in the VPN app. It probably isn't handling the system shutdown procedure properly.

drhender wrote:

One reason I ask is because I've been told that there are apps that don't behave well if that cold restart doesn't occur.

Who told you that?

drhender wrote:

A guy named Johnny. (What difference does it make?)

The only reason I asked is because it sounds like the nonsense that is often posted online.

+1