Memory sticks with different sizes and compatibility?

Question

Iron

If there are 2 sticks: one is 8GB, the second is 4GB, how will this affect the operation and performance of the memory?

Answer 1

If the memory is of the same type, then they are compatible.
If the motherboard allows you to put different sizes, then they are compatible.
If the number of channels is the same, then they are compatible.
It will work at the frequency of the smaller of them.

Answer 2

If 2 bars: one 8GB, the second 4GB

Let's start with this.
So. It is necessary to take into account such factors as:
Clock working purity of RAM in MHz.
Minimum operating purity in MHz. (if one module works at, for example, 1333 MHz. And the other at 1600 MHz, then both modules will work at 1333. Everything will tend to the smaller side).
And it will be very simple. Press the computer start button. If it starts, then praise to something higher, everything works. If something goes wrong, the computer will not start or one of the modules will not be inserted.
I have everything ;)
Thank you for your attention, all the best.

spoiler

P/s
Так всё красиво расписал, не хочу удалять ;)
Развернул комментарии и увидел ссылки на товары.
Исходя из информации вышел. Оба модуля будут работать на чистоте "2400 МГц" Так как я писал выше.