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Disk setup is where preparation becomes a real storage change. Pause before selecting Next. The correct choice depends on the keep-Windows decision—not on which button looks easiest.
Understand what the screen represents
A physical disk is a real SSD, NVMe device, or hard drive. A partition is a defined region on that disk. One physical disk can have several partitions.
A filesystem organizes files inside a partition. Examples include NTFS for many Windows volumes, FAT/VFAT for boot media and EFI partitions, and ext4 for common Linux installations.
The EFI System Partition is a small FAT-formatted partition used by UEFI firmware to find boot files. It is not an ordinary documents partition. Beginners should not format or delete an existing EFI System Partition as a generic cleanup step.
The internal disk is physically installed in the computer. The USB installation media is the removable device currently running the installer. Both can appear in the same list.
Compare the three main choices
| Choice | What it does | Preserves Windows? | Uses full target disk? | Beginner suitability | Main danger | Choose when |
|---|---|---|---|---|---|---|
| Erase disk and install Ubuntu | Replaces the selected disk's partition layout with Ubuntu | No, not on that selected disk | Yes | Guided and simple after a deliberate replace-Windows decision | Selecting the wrong disk permanently removes its data | Ubuntu will be the only system on that entire target disk |
| Install Ubuntu alongside another operating system | Creates or uses suitable space while preserving the detected system | Yes, when the displayed plan is correct | No | Guided choice for a prepared dual boot | Wrong assumptions about BitLocker, free space, or target drive | The installer offers a correct plan and Windows preparation is complete |
| Manual partitioning | Lets the user create, delete, format, and assign partitions | Only if every manual choice is correct | Not necessarily | Advanced | A small mistake can delete data or make systems unbootable | A documented custom layout is genuinely required and understood |
Erase disk and install Ubuntu
- What it does
- Replaces the selected disk's partition layout with Ubuntu
- Preserves Windows?
- No, not on that selected disk
- Uses full target disk?
- Yes
- Beginner suitability
- Guided and simple after a deliberate replace-Windows decision
- Main danger
- Selecting the wrong disk permanently removes its data
- Choose when
- Ubuntu will be the only system on that entire target disk
Install Ubuntu alongside another operating system
- What it does
- Creates or uses suitable space while preserving the detected system
- Preserves Windows?
- Yes, when the displayed plan is correct
- Uses full target disk?
- No
- Beginner suitability
- Guided choice for a prepared dual boot
- Main danger
- Wrong assumptions about BitLocker, free space, or target drive
- Choose when
- The installer offers a correct plan and Windows preparation is complete
Manual partitioning
- What it does
- Lets the user create, delete, format, and assign partitions
- Preserves Windows?
- Only if every manual choice is correct
- Uses full target disk?
- Not necessarily
- Beginner suitability
- Advanced
- Main danger
- A small mistake can delete data or make systems unbootable
- Choose when
- A documented custom layout is genuinely required and understood
Identify the target drive with evidence
Before any guided erase or alongside plan, compare:
- Model: does it match the internal SSD or hard drive?
- Total capacity: is it near the recorded 256 GB, 512 GB, or 1 TB size?
- Context: is it installed internally or is it the USB in your hand?
- Existing partitions: do Windows, recovery, or EFI partitions match the expected computer history?
- Mount point: is a VFAT partition mounted at
/cdrom, identifying the live USB?
Never follow “always select /dev/sda.” A USB can be /dev/sda; an internal SATA drive can also be /dev/sda in another boot. An NVMe disk often appears as /dev/nvme0n1, but model and capacity remain necessary evidence.
Erase disk and install Ubuntu
Choose this only when Ubuntu should replace everything on the selected disk. With multiple physical drives, the installer can let you choose one. A Windows system on a different untouched disk may remain, but that does not make a mistaken target recoverable.
Read the final summary later. It must name the intended internal disk, not the USB or backup drive.
Install Ubuntu alongside another operating system
This guided choice preserves the detected operating system and assigns space to Ubuntu. Review the selected drive and proposed space carefully. Ubuntu 26.04 can support more BitLocker dual-boot situations when suitable space is available, but a visible BitLocker blocker still requires the preparation in Lesson 4.3.
The absence of an Alongside choice is a diagnostic fact, not permission to delete partitions. Check internal-drive visibility, BitLocker, RST, the current disk layout, and available space.
Manual partitioning is an advanced route
The screen lists disks and partitions and can expose controls such as New partition table, format, add, remove, and change. A new partition table replaces the selected disk’s map; it is destructive.
This series does not give one universal dual-boot partition recipe. Disk layouts differ in firmware mode, encryption, recovery partitions, existing filesystems, available space, and number of disks.
Do not:
- Format an existing EFI partition as a routine step.
- Delete a recovery or unknown partition to create space.
- assign a filesystem or mount point you do not understand.
- create a new partition table because the desired disk is absent.
The wrong screen to continue from
If manual partitioning shows only one device around 123 GB, with a VFAT partition and no expected internal disk, that is the USB-only symptom from Lesson 4.1.
Common mistakes and recovery
Confusing a partition with a disk. Follow indentation and total disk rows. A partition such as sda1 belongs to its parent disk.
Using size alone. Two devices can have similar capacities. Match model, connection context, and partitions too.
Selecting Alongside without reviewing the plan. Verify which Windows system and physical disk the installer detected.
Creating a partition table but not confirming installation yet. Stop immediately and do not write more data. Partition recovery is specialist work and not guaranteed; restore from backup if necessary.
Practice
Knowledge check
Explain why /dev/sda cannot identify a target by itself. Then state what New partition table
does: it replaces the selected disk’s partition map and can make existing data inaccessible.
What to learn next
After selecting the correct disk plan—but before the final install—continue to Ubuntu Disk Encryption Options Explained.