diff --git a/include/apple2.dd.h b/include/apple2.dd.h
index f6f563e..b904113 100644
--- a/include/apple2.dd.h
+++ b/include/apple2.dd.h
@@ -140,6 +140,12 @@ struct apple2dd {
     vm_segment *image;
     int image_type;
 
+    /*
+     * This is the means by which we can save the image data back to the
+     * origin stream, if possible.
+     */
+    FILE *stream;
+
     /*
      * A disk drive may be "off" or "on", regardless of whether it's
      * been selected by the peripheral interface.
@@ -182,7 +188,10 @@ extern apple2dd *apple2_dd_create();
 extern int apple2_dd_insert(apple2dd *, FILE *, int);
 extern int apple2_dd_position(apple2dd *);
 extern vm_8bit apple2_dd_read(apple2dd *);
+extern vm_8bit apple2_dd_switch_rw(apple2dd *);
 extern void apple2_dd_eject(apple2dd *);
+extern void apple2_dd_encode(apple2dd *);
+extern void apple2_dd_decode(apple2dd *);
 extern void apple2_dd_free(apple2dd *);
 extern void apple2_dd_map(vm_segment *);
 extern void apple2_dd_set_mode(apple2dd *, int);
@@ -191,7 +200,6 @@ extern void apple2_dd_step(apple2dd *, int);
 extern void apple2_dd_switch_drive(apple2 *, size_t);
 extern void apple2_dd_switch_latch(apple2dd *, vm_8bit);
 extern void apple2_dd_switch_phase(apple2dd *, size_t);
-extern vm_8bit apple2_dd_switch_rw(apple2dd *);
 extern void apple2_dd_turn_on(apple2dd *, bool);
 extern void apple2_dd_write(apple2dd *);
 extern void apple2_dd_write_protect(apple2dd *, bool);
diff --git a/include/apple2.enc.h b/include/apple2.enc.h
index 6f8068b..a33ff9c 100644
--- a/include/apple2.enc.h
+++ b/include/apple2.enc.h
@@ -64,5 +64,6 @@ extern int apple2_enc_sector(vm_segment *, vm_segment *, int, int);
 extern int apple2_enc_sector_header(vm_segment *, int, int, int);
 extern int apple2_enc_track(vm_segment *, vm_segment *, int, int);
 extern vm_segment *apple2_enc_dos(vm_segment *);
+extern vm_segment *apple2_enc_nib(vm_segment *);
 
 #endif
diff --git a/include/vm_segment.h b/include/vm_segment.h
index 481ff77..ecbf0a9 100644
--- a/include/vm_segment.h
+++ b/include/vm_segment.h
@@ -62,6 +62,7 @@ struct vm_segment {
 extern int vm_segment_copy(vm_segment *, vm_segment *, size_t, size_t, size_t);
 extern int vm_segment_copy_buf(vm_segment *, const vm_8bit *, size_t, size_t, size_t);
 extern int vm_segment_fread(vm_segment *, FILE *, size_t, size_t);
+extern int vm_segment_fwrite(vm_segment *, FILE *, size_t, size_t);
 extern int vm_segment_read_map(vm_segment *, size_t, vm_segment_read_fn);
 extern int vm_segment_set(vm_segment *, size_t, vm_8bit);
 extern int vm_segment_set16(vm_segment *, size_t, vm_16bit);
diff --git a/src/apple2.dd.c b/src/apple2.dd.c
index 3605449..1e3b1c4 100644
--- a/src/apple2.dd.c
+++ b/src/apple2.dd.c
@@ -2,8 +2,10 @@
  * apple2.disk_drive.c
  */
 
-#include "apple2.h"
 #include "apple2.dd.h"
+#include "apple2.dec.h"
+#include "apple2.enc.h"
+#include "apple2.h"
 
 /*
  * Create a new disk drive. We do not create a memory segment for the
@@ -70,21 +72,77 @@ apple2_dd_insert(apple2dd *drive, FILE *stream, int type)
     // If we have any data, get rid of it. We'll start fresh here.
     apple2_dd_eject(drive);
 
-    drive->data = vm_segment_create(finfo.st_size);
+    drive->image = vm_segment_create(finfo.st_size);
     drive->track_pos = 0;
     drive->sector_pos = 0;
 
     // Read the data from the stream and write into the memory segment
-    err = vm_segment_fread(drive->data, stream, 0, finfo.st_size);
+    err = vm_segment_fread(drive->image, stream, 0, finfo.st_size);
     if (err != OK) {
         log_critical("Could not read data into disk drive");
         return err;
     }
 
+    drive->stream = stream;
     drive->image_type = type;
+
+    // Now we need to build the data segment
+    apple2_dd_encode(drive);
+
     return OK;
 }
 
+void
+apple2_dd_encode(apple2dd *drive)
+{
+    switch (drive->image_type) {
+        case DD_NIBBLE:
+            drive->data = apple2_enc_nib(drive->image);
+            break;
+
+        case DD_DOS33:
+        case DD_PRODOS:
+            drive->data = apple2_enc_dos(drive->image);
+            break;
+
+        default:
+            log_critical("Unknown image type");
+            exit(1);
+    }
+}
+
+void
+apple2_dd_save(apple2dd *drive)
+{
+    // First bring the image segment back into sync with with the data
+    // segment.
+    apple2_dd_decode(drive);
+
+    if (drive->stream) {
+        rewind(drive->stream);
+        vm_segment_fwrite(drive->image, drive->stream, 0, drive->image->size);
+    }
+}
+
+void
+apple2_dd_decode(apple2dd *drive)
+{
+    switch (drive->image_type) {
+        case DD_NIBBLE:
+            apple2_dec_nib(drive->image, drive->data);
+            break;
+
+        case DD_DOS33:
+        case DD_PRODOS:
+            apple2_dec_dos(drive->image, drive->data);
+            break;
+
+        default:
+            log_critical("Unknown image type");
+            exit(1);
+    }
+}
+
 /*
  * Evaluate the value of the phase_state against the last known phase,
  * and decide from there whether we should step forward or backward by a
@@ -177,8 +235,13 @@ void
 apple2_dd_eject(apple2dd *drive)
 {
     if (drive->data) {
+        // Save off anything else we have left
+        apple2_dd_save(drive);
+
         vm_segment_free(drive->data);
+        vm_segment_free(drive->image);
         drive->data = NULL;
+        drive->image = NULL;
     }
 
     drive->track_pos = 0;
diff --git a/src/vm_segment.c b/src/vm_segment.c
index b77ef47..19557de 100644
--- a/src/vm_segment.c
+++ b/src/vm_segment.c
@@ -176,7 +176,7 @@ vm_segment_copy(vm_segment *dest,
             size_t src_index, 
             size_t length)
 {
-    if (src_index + length >= src->size) {
+    if (src_index + length > src->size) {
         log_critical(
             "Attempt to copy beyond bounds of vm_segment (%d + %d >= %d)",
             src_index,
@@ -186,7 +186,7 @@ vm_segment_copy(vm_segment *dest,
         return ERR_OOB;
     }
 
-    if (dest_index + length >= dest->size) {
+    if (dest_index + length > dest->size) {
         log_critical(
             "Attempt to copy beyond bounds of vm_segment (%d + %d >= %d)",
             dest_index,
@@ -286,6 +286,19 @@ vm_segment_fread(vm_segment *segment, FILE *stream, size_t offset, size_t len)
     return OK;
 }
 
+int
+vm_segment_fwrite(vm_segment *seg, FILE *stream, size_t off, size_t len)
+{
+    fwrite(seg->memory + off, sizeof(vm_8bit), len, stream);
+
+    if (ferror(stream)) {
+        log_critical("Could not write to the file stream: %s", strerror(errno));
+        return ERR_BADFILE;
+    }
+
+    return OK;
+}
+
 /*
  * Change the internal notion of the machine used by map functions
  */