If you don't have a Time Machine back-up hard drive.

You don't [really] have a chance.

After reading quite a few reviews for Apple's latest [free] version of its operating system, I'd been rather wary about upgrading.  I'd been on the fence about it, up until the time my brother said he'd had Mavericks on his computer practically since it came out.  After hearing that he never had any big problems with 10.9, I decided to go ahead and take the chance.  Within about 48 hours, my Mac partition's been reduced to an "EFI Boot" (whatever the shell that means).  I don't have a spare external HD that can function as my Time Machine device.  After attempting to software repair/verify the partition, as well as the harddrive itself, I've essentially dug myself deeper, as I can no longer even access my BOOTCAMP (Windows) partition now. Thus, at some point I need to go ahead and take my computer and get my files (namely my GarageBand and Live projects!) saved (hopefully), before I do a clean install.

Bottom line:

DO. NOT. DOWNLOAD. OS X MAVERICKS.