diff --git a/docs/nixos_build_spec.md b/docs/nixos_build_spec.md
index da6b320..1838187 100644
--- a/docs/nixos_build_spec.md
+++ b/docs/nixos_build_spec.md
@@ -39,7 +39,10 @@ WIPE + install NixOS here:
   - NOTE: device name may appear as /dev/sdb or /dev/sdc depending on boot/USB order; identify by UUID/label/model.
 - Integral300 (ext4) UUID=27febd74-20aa-4a3a-92c1-6fdd1ad7e88e (~298GiB/320GB) (mount at /data)
   - NOTE: device name may change; config always uses /dev/disk/by-uuid.
-- /dev/sde (160GB) ext4 label "XPSystemDrive" (keep)
+- XPSystemDrive (ext4) UUID=82c994f1-9adb-49e4-ba1e-5b6e5ccbd49b (~149GiB/160GB) (KEEP)
+  - Model: HTS541616J9SA00 (Hitachi)
+  - NOTE: device name may appear as /dev/sdb or other /dev/sdX depending on boot/USB order; identify by UUID/label/model.
+  - Observed: `fdisk` currently reports the 160GB device as /dev/sdb (do not rely on this).
 
 Bootloader:
 - systemd-boot, using the existing EFI partition (/dev/nvme0n1p1)