Tutorial: How to Windows+Recalbox+Other Os's Multiboot ?
I've installed recalbox to my old HP Pavilion Laptop's SSD now my RECALBOX working at lightspeed 
I want to share my installation steps with you.
.:: WARNING ::.
SOME PARTS OF THIS TUTORIAL HAS SERIOUS RISKS
I TAKE NO RESPONSIBILITY ABOUT IT
If you don't know what are you doing please cancel or get help from who has knowledge about linux.
Requirements :
Empty HDD (SSD suggested)
Windows 10
Ubuntu (or Linux mint but I've suggest ubuntu)
Pre installed Recalbox to USB disc
Minitool partition wizard (free edition enough) Or other 3rd party partitioning software.
Lets start:
1- Install windows 10 if already installed skip to -> Use 3rd party partitioning software and shrink windows partition.
You need 100+ gb empty area for install other Oss.
2- Create a primary partition for ubuntu installation. 20 GB enough. It must be ext4 file system. (thats why we need 3rd party partitioning software)
3- Create an Extended Partition.
4- Create 3 logical partition for recalbox. Don't forget to give correct labels,
a) Label first partition as "RECALBOX" this will contain main system as FAT32 partition create at least 4GB.
b) Label second partition as "SHARE" this will contain your rom files as exFAT recommended for large discs. At least 50+ GB
c) Label third partition as "OVERLAY" at least 3GB
5- Install Ubuntu to primary partition (you have already created @step2) This will install grub2 boot manager. Now should have multiboot ubuntu and windows 10.
6- Boot to ubuntu.
7- Open ubuntu disks app. Check partitions names and devices like SYSTEM partition as logical inside extended partition as like /dev/sda5
8- Put pre installed Recalbox USB disc. Now you can see USB disc partitions in ubuntu disks app. Note all partition device info.
My usb disc shown as
SYSTEM partition at /dev/sdc1
SHARE partition at /dev/sdc2
OVERLAY partition at /dev/sdc3
9- Open a terminal. Write these command VERY CAREFULLY. I suggest triple check all.
a- we copy RECALBOX partition in USB to system partition labeled RECALBOX in your SSD. The command is;
sudo dd if=/dev/sdc1 of=/dev/sda5 status=progress
b- we copy SHARE partition in USB to rom partition labeled SHARE in your SSD. The command is;
sudo dd if=/dev/sdc2 of=/dev/sda6 status=progress
c- we copy OVERLAY partition in USB to partition labeled OVERLAY in your SSD. The command is;
sudo dd if=/dev/sdc3 of=/dev/sda7 status=progress
You must change /dev/sdcxx and /dev/sdaxx ------> xx must be your partition location in your USB and SSD discs.
I've highly suggest you note all partitions locations to somewhere like paper.
10- Your terminal already opened. Now install ubuntu grub customizer with command
sudo apt install grub-customizer
11- Open Grub Customizer app.Now you must see 2 OS in boot menu. Windows 10 and Ubuntu.
12- Click Notepad+ like button for add our recalbox installation to boot menu.
13- Now we need write some parameters here like,
a- in Name box - Give name like MY RECALBOX SYSTEM
b- in Type box - Select Other
c- Empty area - write these
set root=(hd1,5) --------> This must be RECALBOX partition in your SSD which we noted before. Change with yours like (hd0,5) or (hd1,7) whatever
set gfxpayload=auto
linux /boot/linux label=RECALBOX console=tty3 quiet loglevel=0
initrd /boot/initrd.gz
14- Press ok button. Now we are at main window of grub customizer. You should have 3 Os now. Windows-Ubuntu-MY RECALBOX SYSTEM
15- Press save button at upper left.
16- Remove USB and reboot.
17- Now you must see your Recalbox in menü. Select it and boot your recalbox.
18- If you want to add rom files to your recalbox, you can boot to ubuntu mount recalbox SHARE partition as drive. Copy all roms to their own directory like MAME, NEO GEO etc.
Here is my boot menu and recalbox pics.
