Macintosh 64K and 128K ROMs: Startup Differences

How can I tell what ROMs a Macintosh 512K has? What are some differences that I can see without looking at the logic board?
The 64K ROMs and 128K ROMs have different ways of starting up and looking for the System file on a disk.

To tell if your Macintosh 512K has 64K or 128K ROMs, check either of the following:

Choose "About the Finder" in the Apple Menu. At the bottom left corner of the box that appears, the amount of RAM (in K) that the Macintosh has will be displayed.

a) A K without a period following it indicates the 64K ROMs.
b) A K with a period following it indicates the 128K ROMs.

Look at the title bar of any window:
a) Windows with only a close box in the title bar indicate the 64K ROMs.
b) Windows with a close box and a resize or zoom box in the title bar indicate the 128K ROMs.

Now that you can identify which ROMs are in your Macintosh, here's how each type boots:

Macintosh 512K with 64K ROMs
The startup procedure looks first at the internal floppy drive and then the external drive. If the Macintosh does not find the System file on a disk in the internal drive, it ejects the disk there and looks to the external drive. If there is no system file on the disk in the external drive, that disk is also ejected.

The Hard Disk 20 Startup disk in the internal drive will load the HFS file system and drivers into memory and eject the disk if there is a system folder on the HD 20.

Macintosh Plus or Macintosh 512K Extended with 128K ROMs
The startup procedure looks for a valid system folder in these devices in the following order:
Published Date: Feb 18, 2012