file size Tiff vs Psd

Does anyone know exactly why .psd files save out in a smaller size than a .tiff

In other words, if I create a tif then duplicate that same file and save it as a .psd, the .psd is significantly smaller than the identical tiff. This seems to hold true for flat files and layered files.

anyone?

This is only true if you save the PSD without the backwards compatibility option...that's the differences in sizes. TIFF can actually use Zip compression with is more efficient than PSD's RLE compression.

Where is that option and what is it exactly?

Thanks Jeff..I enjoy your work.

Ok..I just found what you were talking about and did a test with the maximize compatibility on and off. I see the difference.

thanks again