diff --git a/toh_disk.c b/toh_disk.c
index 5e2527a..419d329 100644
--- a/toh_disk.c
+++ b/toh_disk.c
@@ -9,3 +9,74 @@
  * Implementation of toh_disk.h.
  * ----------------------------------------------------------
  */
+
+#include "toh_disk.h"
+#include "config.h"
+#include <stdlib.h>
+
+struct DiskData {
+   unsigned short size;
+};
+
+/**
+ * Provides the instance of the disk with the given size.
+ * Valid disk sizes are from 1 to MAX_DISKS.
+ * 
+ * @param size The size of the desired disk.
+ * @return The disk of the given size or 0, 
+ *         if no such disk is available.
+ */
+Disk td_get_disk(unsigned short size) {
+    if(size < 1 || size > MAX_DISKS) {
+        return 0;
+    }
+
+    Disk disk = (Disk)calloc(sizeof(struct DiskData), 1);
+    disk->size = size;
+    return disk;
+}
+
+/**
+ * Determines whether or not the given disk is valid.
+ * It is valid if it is not 0 and has a size between 1 and MAX_DISKS.
+ * 
+ * @param disk The disk in focus of this ADT.
+ * @return True if the disk is valid, false otherwise.
+ */
+bool td_is_valid(Disk disk) {
+    if (disk == 0 || disk->size < 1 || disk->size > MAX_DISKS) {
+        return false;
+    }
+
+    return true;
+}
+
+/**
+ * Provides the size of the given disk.
+ * 
+ * @param disk The disk in focus of this ADT.
+ * @return The size of the disk, if it is valid or 0 otherwise.
+ */
+unsigned short td_get_size(Disk disk) {
+    if (!td_is_valid(disk)) {
+        return 0;
+    }
+
+    return disk->size;
+}
+
+/**
+ * Compares the size of the candidate disk with size of the given disk.
+ * 
+ * @param disk The disk in focus of this ADT.
+ * @param smaller_candidate The disk to evaluate.
+ * @return True if the 'smaller_candidate' disk is smaller than the 
+ * given disk of this ADT and both disks are valid, false otherwise.
+ */
+bool td_is_smaller(Disk disk, Disk smaller_candidate) {
+    if (!td_is_valid(disk) || !td_is_valid(smaller_candidate)) {
+        return false;
+    }
+
+    return disk->size > smaller_candidate->size;
+}
\ No newline at end of file
diff --git a/toh_disk.h b/toh_disk.h
index 48c16c6..ea5516e 100644
--- a/toh_disk.h
+++ b/toh_disk.h
@@ -20,7 +20,7 @@
 #include <stdbool.h>
 
 /** Declares a disk. */
-typedef struct TohDiskData* TohDisk;
+typedef struct DiskData* Disk;
 
 /**
  * Provides the instance of the disk with the given size.
@@ -30,7 +30,7 @@ typedef struct TohDiskData* TohDisk;
  * @return The disk of the given size or 0, 
  *         if no such disk is available.
  */
-TohDisk td_get_disk(unsigned short size);
+Disk td_get_disk(unsigned short size);
 
 /**
  * Determines whether or not the given disk is valid.
@@ -39,7 +39,7 @@ TohDisk td_get_disk(unsigned short size);
  * @param disk The disk in focus of this ADT.
  * @return True if the disk is valid, false otherwise.
  */
-bool td_is_valid(TohDisk disk);
+bool td_is_valid(Disk disk);
 
 /**
  * Provides the size of the given disk.
@@ -47,7 +47,7 @@ bool td_is_valid(TohDisk disk);
  * @param disk The disk in focus of this ADT.
  * @return The size of the disk, if it is valid or 0 otherwise.
  */
-unsigned short td_get_size(TohDisk disk);
+unsigned short td_get_size(Disk disk);
 
 /**
  * Compares the size of the candidate disk with size of the given disk.
@@ -57,6 +57,6 @@ unsigned short td_get_size(TohDisk disk);
  * @return True if the 'smaller_candidate' disk is smaller than the 
  * given disk of this ADT and both disks are valid, false otherwise.
  */
-bool td_is_smaller(TohDisk disk, TohDisk smaller_candidate);
+bool td_is_smaller(Disk disk, Disk smaller_candidate);
 
 #endif
\ No newline at end of file