High Sierra.

When I put the Mac to sleep, what actually stays running during sleep?

Is the RAM kept powered. Just curious if there is actual
circuitry/hardware designed to allow the RAM to remain powered but CPU
and other components powered down fully. or does the CPU just go into a
"chill-out" mode where it thinks with only 1 core and very very slowly?

I know that the ethernet powers down (because it takes a noticeable
number of seconds for negotiation to turn it back on after waking up the
Mac. Also during sleep, my external disk enclosures indicate loss of
connection to the trash can (so more than just disks spinning down).

In "power nap" periods, does the computer become fully functional,
ethernet and drives powered back on, and any/all processes give CPU time
during the short wake up period? Or is it a very specific set of
processes allowed to get CPU? (aka: Apple Mail only, but not Thunderbird
or other mail clients).

Which comes to:

Is there any configurability to Power Nap?
-how often it wakes up and for how long?
-which processes are allowed to run?

On 14-Jul-2021 at 11:56:13AM PDT, "JF Mezei" <jfmezei.spamnot@vaxination.ca>
wrote:

> High Sierra.
>
> When I put the Mac to sleep, what actually stays running during sleep?
>
> Is the RAM kept powered. Just curious if there is actual
> circuitry/hardware designed to allow the RAM to remain powered but CPU
> and other components powered down fully. or does the CPU just go into a
> "chill-out" mode where it thinks with only 1 core and very very slowly?
>
> I know that the ethernet powers down (because it takes a noticeable
> number of seconds for negotiation to turn it back on after waking up the
> Mac. Also during sleep, my external disk enclosures indicate loss of
> connection to the trash can (so more than just disks spinning down).
>
> In "power nap" periods, does the computer become fully functional,
> ethernet and drives powered back on, and any/all processes give CPU time
> during the short wake up period? Or is it a very specific set of
> processes allowed to get CPU? (aka: Apple Mail only, but not Thunderbird
> or other mail clients).
>
> Which comes to:
>
> Is there any configurability to Power Nap?
> -how often it wakes up and for how long?
> -which processes are allowed to run?

I did a google search so I was clear about what you're asking since I don't
allow my desktop to sleep. The display and drives go quiessent, but the
processor is still running. If the display were active, you'd see the system
clock ticking away the seconds. It's one of the ways I can tell if my system
is really and totally hosed--the processor stops updating the clock and it
freezes.

https://askubuntu.com/questions/369760/what-are-the-differences-between-sleep-standby-suspend-and-hibernate-in-ubuntu

This explains sleep vs. suspend. Think of sleep as a 'low power mode' but
still running. Suspend is like closing the lid on your laptop. When you open
the lid, the system 'resumes' and the date/time display changes from when you
closed the lid. Wake-On-LAN is a feature that allows a special interrupt
generated by a network packet to trigger the wake from sleep mode.

Otherwise normal processes like cron jobs aren't processed. sleep and suspend
are function of the kernel and the hardware and not configurable AFAIK, so you
can't say "allow mail to run during this mode". If you need things to be
running, don't allow your system to sleep. Turn off the display and allow the
drives to spin down (irrelevant with SSD) but stay running. If you have a
laptop, don't close the lid and leave it plugged into the power brick.

I only think you'll see hibernate if you suspend a running VM. A snapshot of
the running system is written to disk and will be resumed when you resume the
VM.

--
DeeDee, don't press that button! DeeDee! NO! Dee...