diff --git a/include/apple2.dd.h b/include/apple2.dd.h
index fe12902..f6f563e 100644
--- a/include/apple2.dd.h
+++ b/include/apple2.dd.h
@@ -16,6 +16,19 @@ typedef struct apple2dd apple2dd;
 #include "vm_bits.h"
 #include "vm_segment.h"
 
+/*
+ * Define the kind of image types that our disk media currently has. The
+ * image type is something which is given to us when the disk is
+ * "inserted", and it can't be changed during machine operation.
+ * Well--it could--but we don't have a good reason to do so.
+ */
+enum apple2_dd_type {
+    DD_NOTYPE,
+    DD_DOS33,
+    DD_PRODOS,
+    DD_NIBBLE,
+};
+
 /*
  * These are the possible modes a drive can be in.
  */
@@ -116,10 +129,16 @@ struct apple2dd {
     int sector_pos;
 
     /*
-     * The data field is where the actual byte data for the image is
-     * kept.
+     * The data segment holds the literal data that the software running
+     * in an Apple II would expect to see when accessing the device,
+     * which is to say, data that is 6-and-2 encoded. The image segment
+     * holds the data we literally read from a disk image file, which
+     * (in most cases) is not 6-and-2 encoded. We also define an image
+     * type (see apple2_dd_type for enums).
      */
     vm_segment *data;
+    vm_segment *image;
+    int image_type;
 
     /*
      * A disk drive may be "off" or "on", regardless of whether it's
@@ -160,7 +179,7 @@ struct apple2dd {
 extern SEGMENT_READER(apple2_dd_switch_read);
 extern SEGMENT_WRITER(apple2_dd_switch_write);
 extern apple2dd *apple2_dd_create();
-extern int apple2_dd_insert(apple2dd *, FILE *);
+extern int apple2_dd_insert(apple2dd *, FILE *, int);
 extern int apple2_dd_position(apple2dd *);
 extern vm_8bit apple2_dd_read(apple2dd *);
 extern void apple2_dd_eject(apple2dd *);
diff --git a/src/apple2.c b/src/apple2.c
index 96918b5..57340b4 100644
--- a/src/apple2.c
+++ b/src/apple2.c
@@ -213,6 +213,8 @@ apple2_is_double_video(apple2 *mach)
 /*
  * Try to "boot" the apple2 machine. Look for input sources indicated in
  * the option system and load those into our disk drives.
+ *
+ * FIXME: we need to get the image type from the file name used
  */
 int
 apple2_boot(apple2 *mach)
@@ -223,7 +225,7 @@ apple2_boot(apple2 *mach)
     // Do we have any disks?
     stream = option_get_input(1);
     if (stream) {
-        err = apple2_dd_insert(mach->drive1, stream);
+        err = apple2_dd_insert(mach->drive1, stream, DD_DOS33);
         if (err != OK) {
             log_critical("Unable to insert disk1 into drive");
             return err;
@@ -232,7 +234,7 @@ apple2_boot(apple2 *mach)
 
     stream = option_get_input(2);
     if (stream) {
-        err = apple2_dd_insert(mach->drive2, stream);
+        err = apple2_dd_insert(mach->drive2, stream, DD_DOS33);
         if (err != OK) {
             log_critical("Unable to insert disk2 into drive");
             return err;
diff --git a/src/apple2.dd.c b/src/apple2.dd.c
index ac9a4fc..3605449 100644
--- a/src/apple2.dd.c
+++ b/src/apple2.dd.c
@@ -25,6 +25,7 @@ apple2_dd_create()
     // will depend on the disk you insert. For example, a DOS 3.3 or
     // ProDOS disk will have 140k, but a NIB file would have more.
     drive->data = NULL;
+    drive->image = NULL;
 
     drive->locked = false;
     drive->track_pos = 0;
@@ -34,6 +35,7 @@ apple2_dd_create()
     drive->mode = DD_READ;
     drive->phase_state = 0;
     drive->last_phase = 0;
+    drive->image_type = DD_NOTYPE;
 
     return drive;
 }
@@ -44,7 +46,7 @@ apple2_dd_create()
  * something we cannot accept.
  */
 int
-apple2_dd_insert(apple2dd *drive, FILE *stream)
+apple2_dd_insert(apple2dd *drive, FILE *stream, int type)
 {
     struct stat finfo;
     int err;
@@ -79,6 +81,7 @@ apple2_dd_insert(apple2dd *drive, FILE *stream)
         return err;
     }
 
+    drive->image_type = type;
     return OK;
 }
 
diff --git a/tests/apple2.dd.c b/tests/apple2.dd.c
index b4fdd98..613a0b7 100644
--- a/tests/apple2.dd.c
+++ b/tests/apple2.dd.c
@@ -21,6 +21,8 @@ TestSuite(apple2_dd, .init = setup, .fini = teardown);
 Test(apple2_dd, create)
 {
     cr_assert_eq(drive->data, NULL);
+    cr_assert_eq(drive->image, NULL);
+    cr_assert_eq(drive->image_type, DD_NOTYPE);
     cr_assert_eq(drive->track_pos, 0);
     cr_assert_eq(drive->sector_pos, 0);
     cr_assert_eq(drive->online, false);
@@ -40,13 +42,14 @@ Test(apple2_dd, insert)
     drive->sector_pos = 33;
 
     stream = fopen("../data/zero.img", "r");
-    cr_assert_eq(apple2_dd_insert(drive, stream), OK);
+    cr_assert_eq(apple2_dd_insert(drive, stream, DD_DOS33), OK);
     cr_assert_eq(drive->track_pos, 0);
     cr_assert_eq(drive->sector_pos, 0);
+    cr_assert_eq(drive->image_type, DD_DOS33);
     fclose(stream);
 
     stream = fopen("../data/bad.img", "r");
-    cr_assert_eq(apple2_dd_insert(drive, stream), ERR_BADFILE);
+    cr_assert_eq(apple2_dd_insert(drive, stream, DD_DOS33), ERR_BADFILE);
     fclose(stream);
 }