diff --git a/shell/README.md b/shell/README.md
index 2843d0f1..3431638a 100644
--- a/shell/README.md
+++ b/shell/README.md
@@ -22,7 +22,13 @@ Currently runs a tiny dialect of Lisp. Steps to run it from the top-level:
   dd if=shell/data.limg of=data.img conv=notrunc
   ```
 
-  Run with data disk (and 2GB of RAM):
+  Equivalently, use `tools/image-data`.
+
+  ```sh
+  tools/image-data 10 < shell/data.limg
+  ```
+
+3. Run with data disk (and 2GB of RAM):
   ```sh
   qemu-system-i386 -m 2G -hda code.img -hdb data.img
   ```
diff --git a/tools/image-data b/tools/image-data
new file mode 100755
index 00000000..fe46e310
--- /dev/null
+++ b/tools/image-data
@@ -0,0 +1,12 @@
+#!/bin/sh
+# Create a disk image containing some (text) data.
+
+if [ $# -eq 0 ]
+then
+  echo "Fill disk of some capacity (in MB) from stdin"
+  echo "usage: image-data capacity"
+  exit 1
+fi
+
+dd if=/dev/zero of=data.img count=$(($1*2016))  # 32 * 63 sectors/track
+dd of=data.img conv=notrunc