[Shiunbird]

You made me curious.

I can open TIFF files from my Nikon D850 in Photoshop and they work OK.
The largest file I have is a photograph in Lisbon and used (modern) Photoshop camera RAW to upscale the original NEF file from my D850.

The resulting TIFF file is 16.512 x 11.008 pixels, 2.54 GB.
The original PSD file, saved in Photoshop 2021(ish), is 1.93GB and my Octane opens it fine, too.

My Octane is a 1x400 MHz with 1.5GB of RAM. Opening the file always takes a while because it comes via NFS 100Mbit.

Changing from 48 to 24 bits so I could try filters took 60s. I tried applying a zigzag distortion. It took a good while for the preview window to appear, but when I tried to run it, it complained it had not enough memory.
Gaussian blur 48px ran in 2:30 mins.

So I tried the standard imageview and it opens the image fine. Scrolling is surprisingly speedy, better than photoshop. But when I tried to open the histogram, it complained it had no memory. I am happy that imageview is up to the task of at least opening the file.

Then I tried to convert the PSD to JPG using image independence and it didn't even try, complaining it had no memory.

So yes, I doubt my Pentium 500 with Windows 98 would manage to do any of that! =)))
I am also curious to what kind of software was used to process the really really huge image files back in the day - I always think of stitching lots of satellite photos for a high res printed map or the sort.