# Restoring Windows on ASUS T101HA

Complete guide to reverting from Xubuntu back to the original Windows installation.

---

## What you have

| Item | Location | Purpose |
|---|---|---|
| `t101ha.img.zst` | PC: `E:\git\02 cSharp using mono\main\EARS-LINUX\OS\BACKUP\`<br>USB: BACKUP partition | Full byte-exact disk image, 17GB compressed |
| `parts.txt` | Same locations | Partition table reference |
| `window-key.txt` | Same locations | Windows product key |

**Verified:** SHA256 `CBD4348ACB6777D5110D00F15FD67A6CBABE96152B628E503A8F2F6127E4EB63` (both copies identical)

**Image expands to:** 62,537,072,640 bytes — exact match to device size

---

## Device reference

- **Internal eMMC:** `/dev/mmcblk1` — ~58GiB (62,537,072,640 bytes)
- **Firmware:** 64-bit UEFI (confirmed via `fw_platform_size`)
- **Original layout:** ESP, Microsoft reserved, Windows (`p3`), recovery (`p4`)

> **WARNING:** Verify the device with `lsblk` every time. Device names can shift between boots.

---

## Method 1 — Full image restore (recommended)

Restores the exact original system: Windows activated, ASUS recovery partition, everything.

### Preparation

If the image lives on the PC, copy it back to the USB stick's BACKUP partition first. Restoring over a network is not recommended.

### Steps

**1. Boot the Ventoy live session**

Power off fully. Hold F2, tap power, keep holding. Confirm Secure Boot is disabled, boot from USB, select the Xubuntu ISO, choose "Try Xubuntu".

**2. Identify the devices**

```bash
lsblk -o NAME,SIZE,FSTYPE,LABEL,MOUNTPOINT
```

Confirm:
- eMMC = the **~58GiB** device (`mmcblk1`)
- USB = the **~115GiB** device with Ventoy/VTOYEFI/BACKUP partitions

**3. Mount the backup**

```bash
sudo mkdir -p /mnt/backup
sudo mount /dev/sda3 /mnt/backup
ls -lh /mnt/backup
```

Adjust `sda3` to match the BACKUP partition from step 2.

**4. Verify the image before writing**

```bash
zstd -t /mnt/backup/t101ha.img.zst
```

Must complete without error. If it fails, use the PC copy instead — do not proceed with a corrupt image.

**5. Restore**

```bash
sudo blockdev --getsize64 /dev/mmcblk1
```

Confirm this prints `62537072640`. Then:

```bash
zstd -dc /mnt/backup/t101ha.img.zst | sudo dd of=/dev/mmcblk1 bs=4M status=progress
sync
```

> **WARNING:** `of=` is the destructive direction. Everything on that device is erased. Read the command twice before pressing Enter.

Takes 1–2 hours. Do not interrupt it, and do not run anything else — 2GB RAM.

**6. Finish**

```bash
sync
sudo umount /mnt/backup
sudo poweroff
```

Remove the USB stick. Power on. Windows should boot, activated, exactly as it was.

### With a progress bar

```bash
sudo apt install -y pv
sudo sh -c 'zstd -dc /mnt/backup/t101ha.img.zst | pv -s 62537072640 | dd of=/dev/mmcblk1 bs=4M'
```

---

## Method 2 — Recover files only (non-destructive)

To extract files from the Windows image without wiping Xubuntu. Requires ~58GB free space.

```bash
zstd -d /path/to/t101ha.img.zst -o /tmp/full.img
sudo losetup -fP --show /tmp/full.img
```

Note the loop device it prints (e.g. `/dev/loop0`), then:

```bash
sudo mkdir -p /mnt/win
sudo mount -o ro /dev/loop0p3 /mnt/win
```

Windows lives on partition 3. Browse `/mnt/win`, copy what you need.

Cleanup:

```bash
sudo umount /mnt/win
sudo losetup -d /dev/loop0
rm /tmp/full.img
```

If mount fails with a BitLocker error, the partition is encrypted — you'll need the recovery key from https://account.microsoft.com/devices/recoverykey

---

## Method 3 — Clean Windows install (image lost)

Last resort. The product key is stored in firmware (ACPI MSDM table), so a clean install self-activates without entering anything.

1. Download the Windows 10 ISO from Microsoft on the PC
2. Write it to USB with Rufus — **GPT**, **UEFI** target
3. Boot the tablet from it, install to the internal eMMC
4. Activation happens automatically from firmware

**Caveats:**
- The ASUS recovery partition is not restored
- Cherry Trail drivers may need manual installation from ASUS support
- **Windows 10 is past end of support (October 2025), and this hardware cannot run Windows 11** — a restored image is a supported-nothing situation either way, but a clean install is strictly worse

---

## Recovering the product key

From Linux, on the running tablet:

```bash
sudo strings /sys/firmware/acpi/tables/MSDM | tail -1
```

From the saved file:

```bash
cat /mnt/backup/window-key.txt; echo
```

From Windows:

```powershell
(Get-CimInstance SoftwareLicensingService).OA3xOriginalProductKey
```

**Note:** viewing `window-key.txt` in Notepad may show CJK garbage — it's an encoding guess, not corruption. Read it on Linux with `cat`, or open it in VS Code and set encoding to UTF-8.

---

## Verifying image integrity

Quick check (structural):

```bash
zstd -t t101ha.img.zst
```

Full check (byte count vs device):

```bash
DEV=$(sudo blockdev --getsize64 /dev/mmcblk1)
IMG=$(zstd -dc /path/to/t101ha.img.zst | wc -c)
echo "device: $DEV"
echo "image:  $IMG"
test "$DEV" = "$IMG" && echo MATCH || echo MISMATCH
```

Compare copies (PowerShell):

```powershell
Get-FileHash 'path\to\t101ha.img.zst' -Algorithm SHA256
```

> **WARNING:** `[ "$DEV" = "$IMG" ]` requires spaces inside the brackets. Without them the shell reports "command not found" and prints MISMATCH regardless of the actual values. Use `test` to avoid this.

---

## Troubleshooting

**Restore finishes but won't boot**

Check Secure Boot in BIOS — re-enable it, since the original Windows install expects it. Confirm the boot order lists Windows Boot Manager.

**`dd` reports "No space left on device"**

Wrong target device. Verify with `lsblk` that you're writing to the ~58GiB eMMC.

**Image fails `zstd -t`**

Use the other copy. If both fail, fall back to Method 3.

**Progress appears frozen**

Check it's actually stalled before interrupting:

```bash
ps -eo pid,stat,cmd | grep -v grep | grep -E 'dd|zstd'
sudo dmesg | tail -30
```

STAT `D` plus `mmc` errors in dmesg indicates bad sectors. STAT `R`/`S` with a clean dmesg means it's just slow — eMMC on this tablet throttles when warm.

**"read kernel buffer failed"**

`dmesg` needs root here: `sudo dmesg`

---

## Notes

- Keep both copies of the image. The USB stick is a single point of failure.
- Restoring reverts to the disk state as of **27 July 2026**. Nothing created in Xubuntu survives.
- Do a full `zstd -t` on whichever copy you plan to use *before* wiping anything.
- Original image created with: `sudo zstd -1 -T0 -f -o /mnt/backup/t101ha.img.zst /dev/mmcblk1`