diff --git a/doc/syscalls.md b/doc/syscalls.md
index 63c0009..54d748b 100644
--- a/doc/syscalls.md
+++ b/doc/syscalls.md
@@ -470,10 +470,22 @@ Argument Structure:
     };
 ```
 
+Device drivers in 65X-DOS identify themselves to the kernel by
+means of their "major number" -- the index into the internal
+device driver table at which the device driver's address can
+be found. Specific devices managed by a driver are distinguished
+from each other by "minor number" -- an arbitrary number which
+holds meaning only to the driver.
+
 Each device driver in 65X-DOS registers one or more major/minor
-number pairs to one or more "default" aliases. These aliases are
+number pairs to one or more "default" names. These aliases are
 what appear in a fully qualified pathname for a file before the
-`:` separator character.
+`:` separator character. You might compare this to a "drive letter"
+in MS-DOS type systems, or to entries in the `/dev` directory on
+a Unix-like system. For example, the SD card driver might register
+the device name `sd0` for the first SD card. Drivers which do not
+expose file-like functionality still expose default names, because
+they use the `ioctl` interface to control their settings.
 
 This call attempts to add a secondary name to an existing device.
 This alias will work exactly like the default name, which will still