Excel: CPU Usage

Hi,

I am currently working with a largish .xlsb file (11 sheets, about 20*300,000 cells each). And quite out of the blue, the file became a real pain in the neck. After I scroll about halfway down (and, obviously, to any position for the rest of the rows below), CPU usage skyrockets to about 97% and stays at that level for a VERY long time. Then – without me doing anything – drops to 1% ... only to return to 97% in about 20-30 seconds. And then the cycle repeats itself over and over. And me still doing absolutely nothing. If I scroll to the first row, CPU usage drops to 1% almost instantly and stays there....

Cells only have a couple of CF formulas (alternate row shading and such), and that's about it.
Could you explain, why this weird behavior? and what can I do to make Excel stop fooling around?

You are saying that your file is 100% data, no formulas, except for CF?

File size is 34.4 Mb.
It can't be the CF rules. I've made a copy of the file, cleared all CF formatting, but Excel is still messing with my nervous system... What's bugging me is that I am not doing anything. Excel has no event for scrolling. Yet the moment I touch that scroll bar, Excel starts to freak out...

Can't upload a copy, sorry. Way too many things to remove or change to make it OK for sharing.

11 sheets with 6 million cells filled per sheet. Although excel has room to do that, the evidence shows it shouldn't be done.

Do you really need 11 sheets with 20 * 300K rows? I can't think of any use case for Excel where you'd need to have all that info in single workbook.

If you don't have any sort of calculation on it, I'd imagine it will be more of an issue with RAM usage.

I mocked up test workbook holding same amount of cells & sheets, each cell populated with decimal number with maximum significant digits.
Using Excel 2019 64bit install, with all superfluous animations turned off and hardware graphics acceleration turned off.
i7-3630QM 2.4 GHz, 4 core (8 thread).

CPU usage peaked at around 35% usage and was never an issue (applying filtering, scroll up & down, zoom etc).
On the other hand, RAM usage was high, using up 6~7 GB of RAM.

My guess, is that you have hardware acceleration turned on, and you may also have a lot of custom/different formats applied (font, cell, border, CF etc) to ranges.

Edit: Oh, by the way, test file size was 650 MB.