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EPSON PC AX PORTABLE MS-DOS 4.01 OEM RELEASE & BIOS SETUP UTILITY
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DISK1.IMG - Serial D-TH-2,1-4.90.1 - MS-DOS 4.01 Referenz-Diskette (Reference Disk - contains BIOS setup and diagnose applications)
DISK2.IMG - Serial A-TH-2,1-4.90.1 - MS-DOS 4.01 Installations-Diskette 1 (Installation Disk 1)
DISK3.IMG - Serial B-TH-2,1-4.90.1 - MS-DOS 4.01 Installations-Diskette 2 (Installation Disk 2)
DISK4.IMG - Serial C-TH-2,1-4.90.1 - MS-DOS 4.01 Shell-Diskette (Shell Disk)


These floppies came with my "EPSON PC AX Portable", which is a 12MHz 286 Laptop built in 1988.
The floppies were not readable under Windows 3.1 via WinImage 5 (every 2nd sector couldn't be found, same on my main Win10 machine with USB floppy), unfortunately. 
I had to use a less-common utility called DSKIMAGE to successfully backup them. I wrote the images back to different floppies and they worked (there are no bad sectors).

All images can be written back to floppy via the included DSKIMAGE.COM application (works on 8086 and above)
As they are all in 720KB IBM format, just use the following command (0: stands for the drive letter A:, 1: would be B:)
DSKIMAGE.COM DISK1.IMG 0:80:2:9
A documentation about various IBM formats can be found in Wikipedia: https://en.wikipedia.org/wiki/List_of_floppy_disk_formats#Logical_formats
