Bootable media contains three essential components:

1. Bootloader (like GRUB, SYSLINUX, or Windows Boot Manager)
2. Partition table with boot flag set
3. Operating system files in the correct structure

The most reliable cross-platform tool is dd on Linux/macOS or Rufus on Windows:

# Linux/macOS terminal command
dd if=/path/to/iso of=/dev/sdX bs=4M status=progress && sync

# Windows (PowerShell alternative)
Start-Process rufus.exe -ArgumentList "--dd-image --device \\.\PhysicalDriveX --image \path\to\iso"

For problematic ISOs like Windows 7 or OEM recovery disks:

# Extract ISO contents first
7z x recovery.iso -oUSB_DRIVE

# Then manually install bootloader
bootsect /nt60 X: /force /mbr

Here's a Bash script that handles multiple scenarios:

#!/bin/bash
ISO=$1
DEVICE=$2

check_iso_type() {
  if file "$ISO" | grep -q "DOS/MBR"; then
    echo "MBR"
  else
    echo "UEFI"
  fi
}

case $(check_iso_type) in
  "MBR")
    dd if="$ISO" of="$DEVICE" bs=4M conv=fdatasync
    ;;
  "UEFI")
    mkfs.fat -F32 "$DEVICE"
    mount "$DEVICE" /mnt
    bsdtar -xvf "$ISO" -C /mnt
    umount /mnt
    ;;
esac

Use these commands to verify your USB was created correctly:

# Check partition table
fdisk -l /dev/sdX

# Verify boot files (Windows)
dir X:\bootmgr

# Check for Linux bootloader
file --dereference /sys/firmware/efi/efivars

• For UEFI systems: Ensure FAT32 formatting
• MBR disks: Set active partition flag
• Secure Boot: May require disabling or signing bootloader
• OEM disks: Often need special drivers - check manufacturer docs

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Before converting physical media to USB, we need to understand what makes devices bootable:

• Boot Sector: Contains machine code for initial system startup (512 bytes)
• Bootloader: GRUB, NTLDR, or BOOTMGR that loads the OS kernel
• File System: FAT32 for BIOS, NTFS/exFAT for UEFI systems

Here are three reliable approaches that work across Windows, Linux, and macOS:

Method 1: Using dd (Linux/macOS)

# Identify USB device (BE CAREFUL - this will erase target device)
lsblk
# Write ISO directly (replace /dev/sdX with your USB)
sudo dd if=your_image.iso of=/dev/sdX bs=4M status=progress && sync

Method 2: Using Rufus (Windows)

For Windows-based conversions:

1. Download Rufus (https://rufus.ie/)
2. Select USB device
3. Choose "ISO Image" mode
4. Set partition scheme (MBR for BIOS, GPT for UEFI)
5. Click Start

Method 3: Ventoy (Multi-OS Solution)

This advanced tool creates a bootable USB that can hold multiple ISOs:

# Linux installation
wget https://github.com/ventoy/Ventoy/releases/download/v1.0.88/ventoy-1.0.88-linux.tar.gz
tar -xzf ventoy-*.tar.gz
cd ventoy-*
sudo ./Ventoy2Disk.sh -i /dev/sdX

For Windows 7/10/11 ISOs, Microsoft provides an official tool:

1. Download Media Creation Tool
2. Select "Create installation media"
3. Choose USB flash drive option
4. Wait for completion

For developers needing custom setups, here's how to modify GRUB:

# After mounting USB:
sudo mount /dev/sdX1 /mnt
sudo grub-install --root-directory=/mnt /dev/sdX
sudo nano /mnt/boot/grub/grub.cfg
# Add custom menu entries

When working with large ISOs (like Windows 11):

• Use USB 3.0+ drives for faster transfer
• Verify write speeds with: hdparm -tT /dev/sdX
• Consider persistent storage for Linux live USBs