I have posted this question in many forums.
Now, I copy it here for the thread starter.
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★★★Thorough Solution for Making a DOS Bootable USB Drive with 4G Large Capacity★★★
After searching the internet for two days, there are many inquiries about making a bootable USB drive with a large capacity (over 2G) for DOS, and it is said to be very difficult to solve. I just happened to buy a 4G one. I finally succeeded after two days. I will share my experience for everyone's reference.
According to the tips on the internet, first download a software called flashboot (version 1.4.0.175), then, according to what many people said, first make a USB drive with the following:
COMMAND.COM
IO.SYS
MSDOS.SYS
Three boot files.
Then, restart and see if it gets stuck on the boot screen and doesn't move?
Don't panic, first pull out the USB drive and restart the computer.
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After booting, first copy the above three files to another disk (you will need them later)
Then, open flashboot again and do it again. This time, don't go the old way.
When prompted: "Get DOS system files from here",
Please click the bottom one: Use built-in FreeDOS (F)
Then, do it as usual.
After completion, go to the USB drive and see if there are two files:
command.com
kernel.sys
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Then copy and paste the three files you just copied to another disk here (when asked to overwrite, just click agree).
Restart the computer, and you will enter DOS (of course, your motherboard needs to support USB boot).