A 3.5 inch (1.44MB) floppy can accomodate 1474560 bytes of data. The boot image is exactly 1474560 bytes in size.
Common mistakes when preparing the boot floppy are:
binary mode when
using FTP.
Some FTP clients default their transfer mode to ascii
and attempt to change any end-of-line characters received to match
the conventions used by the client's system.
This will almost invariably corrupt the boot image. Check the
size of the downloaded boot image: if it is not exactly
that on the server, then the download process is suspect.
To workaround: type binary at the FTP command prompt
after getting connected to the server and before starting the
download of the image.
copy command (or equivalent GUI tool) to
transfer the boot image to floppy.
Programs like copy will not work as the boot
image has been created to be booted into directly. The image has
the complete content of the floppy, track for track, and is not
meant to be placed on the floppy as a regular file.
You have to transfer it to the floppy ``raw'', using the
low-level tools (e.g. fdimage or rawrite)
described in the installation guide to FreeBSD.