diff --git a/src/main/scala/li/cil/oc/client/gui/DynamicGuiContainer.scala b/src/main/scala/li/cil/oc/client/gui/DynamicGuiContainer.scala
index 0cd279c9b..8be2de463 100644
--- a/src/main/scala/li/cil/oc/client/gui/DynamicGuiContainer.scala
+++ b/src/main/scala/li/cil/oc/client/gui/DynamicGuiContainer.scala
@@ -1,7 +1,7 @@
 package li.cil.oc.client.gui
 
 import li.cil.oc.client.Textures
-import li.cil.oc.common.Tier
+import li.cil.oc.common
 import li.cil.oc.common.container.{ComponentSlot, Player}
 import li.cil.oc.util.RenderState
 import li.cil.oc.util.mods.NEI
@@ -40,7 +40,7 @@ abstract class DynamicGuiContainer(container: Container) extends CustomGuiContai
 
   override def drawSlotInventory(slot: Slot) {
     slot match {
-      case component: ComponentSlot if component.tier == Tier.None => // Ignore.
+      case component: ComponentSlot if component.tier == common.Tier.None || component.slot == common.Slot.None => // Ignore.
       case _ =>
         if (!isInPlayerInventory(slot)) {
           GL11.glDisable(GL11.GL_DEPTH_TEST)
diff --git a/src/main/scala/li/cil/oc/common/Slot.scala b/src/main/scala/li/cil/oc/common/Slot.scala
index 4ee0660c4..07922fb6a 100644
--- a/src/main/scala/li/cil/oc/common/Slot.scala
+++ b/src/main/scala/li/cil/oc/common/Slot.scala
@@ -1,5 +1,8 @@
 package li.cil.oc.common
 
+import li.cil.oc.api
+import net.minecraft.item.ItemStack
+
 object Slot {
   val None = "none"
 
@@ -15,7 +18,7 @@ object Slot {
 
   val All = Array(Card, ComponentBus, Container, CPU, Floppy, HDD, Memory, Tool, Upgrade)
 
-  def fromApi(slotType: li.cil.oc.api.driver.Slot) = slotType match {
+  def apply(driver: api.driver.Item, stack: ItemStack, f: Option[ItemStack => api.driver.Slot] = scala.None) = f.getOrElse(driver.slot _)(stack) match {
     case li.cil.oc.api.driver.Slot.Card => Card
     case li.cil.oc.api.driver.Slot.Disk => Floppy
     case li.cil.oc.api.driver.Slot.HardDiskDrive => HDD
@@ -24,6 +27,9 @@ object Slot {
     case li.cil.oc.api.driver.Slot.Tool => Tool
     case li.cil.oc.api.driver.Slot.Upgrade => Upgrade
     case li.cil.oc.api.driver.Slot.UpgradeContainer => Container
-    case _ => None
+    case _ =>
+      val descriptor = api.Items.get(stack)
+      if (descriptor == api.Items.get("componentBus1") || descriptor == api.Items.get("componentBus2") || descriptor == api.Items.get("componentBus3")) ComponentBus
+      else None
   }
 }
diff --git a/src/main/scala/li/cil/oc/common/container/ComponentSlot.scala b/src/main/scala/li/cil/oc/common/container/ComponentSlot.scala
index f467308f6..7512bce61 100644
--- a/src/main/scala/li/cil/oc/common/container/ComponentSlot.scala
+++ b/src/main/scala/li/cil/oc/common/container/ComponentSlot.scala
@@ -1,7 +1,7 @@
 package li.cil.oc.common.container
 
 import cpw.mods.fml.relauncher.{Side, SideOnly}
-import li.cil.oc.common.Tier
+import li.cil.oc.common
 import net.minecraft.entity.player.EntityPlayer
 import net.minecraft.inventory.Slot
 import net.minecraft.item.ItemStack
@@ -21,7 +21,7 @@ trait ComponentSlot extends Slot {
   // ----------------------------------------------------------------------- //
 
   @SideOnly(Side.CLIENT)
-  override def func_111238_b() = tier != Tier.None && super.func_111238_b()
+  override def func_111238_b() = slot != common.Slot.None && tier != common.Tier.None && super.func_111238_b()
 
   override def isItemValid(stack: ItemStack) = inventory.isItemValidForSlot(getSlotIndex, stack)
 
diff --git a/src/main/scala/li/cil/oc/common/inventory/ServerInventory.scala b/src/main/scala/li/cil/oc/common/inventory/ServerInventory.scala
index 6c18a8ece..8519b402c 100644
--- a/src/main/scala/li/cil/oc/common/inventory/ServerInventory.scala
+++ b/src/main/scala/li/cil/oc/common/inventory/ServerInventory.scala
@@ -1,6 +1,6 @@
 package li.cil.oc.common.inventory
 
-import li.cil.oc.api.{Driver, Items}
+import li.cil.oc.api.Driver
 import li.cil.oc.common.{InventorySlots, Slot}
 import net.minecraft.entity.player.EntityPlayer
 import net.minecraft.item.ItemStack
@@ -19,14 +19,6 @@ trait ServerInventory extends ItemStackInventory {
   override def isItemValidForSlot(slot: Int, stack: ItemStack) =
     Option(Driver.driverFor(stack)).fold(false)(driver => {
       val provided = InventorySlots.server(tier)(slot)
-      // TODO remove special code in 1.4 when slot type API changes.
-      val requiredSlot = Slot.fromApi(driver.slot(stack))
-      val isComponentBus = provided.slot == Slot.ComponentBus && {
-        val descriptor = Items.get(stack)
-        descriptor == Items.get("componentBus1") ||
-          descriptor == Items.get("componentBus2") ||
-          descriptor == Items.get("componentBus3")
-      }
-      (requiredSlot == provided.slot || isComponentBus) && driver.tier(stack) <= provided.tier
+      Slot(driver, stack) == provided.slot && driver.tier(stack) <= provided.tier
     })
 }
diff --git a/src/main/scala/li/cil/oc/common/template/AssemblerTemplates.scala b/src/main/scala/li/cil/oc/common/template/AssemblerTemplates.scala
index ee1445693..2ae1dc970 100644
--- a/src/main/scala/li/cil/oc/common/template/AssemblerTemplates.scala
+++ b/src/main/scala/li/cil/oc/common/template/AssemblerTemplates.scala
@@ -60,17 +60,15 @@ object AssemblerTemplates {
     def validate(inventory: IInventory, slot: Int, stack: ItemStack) = validator match {
       case Some(method) => tryInvokeStatic(method, inventory, slot.underlying(), stack)(false)
       case _ => Option(api.Driver.driverFor(stack)) match {
-        case Some(driver) => validateInternal(stack, driver) && Slot.fromApi(driver.slot(stack)) == kind
+        case Some(driver) => Slot(driver, stack) == kind && driver.tier(stack) <= tier
         case _ => false
       }
     }
-
-    protected def validateInternal(stack: ItemStack, driver: api.driver.Item) = driver.tier(stack) <= tier
   }
 
   private def parseSlot(kindOverride: Option[String] = None)(nbt: NBTTagCompound) = {
     val kind = kindOverride.getOrElse(if (nbt.hasKey("type")) nbt.getString("type") else Slot.None)
-    val tier = if (nbt.hasKey("tier")) nbt.getInteger("tier") else Tier.None
+    val tier = if (nbt.hasKey("tier")) nbt.getInteger("tier") else Tier.Any
     val validator = if (nbt.hasKey("validator")) Option(getStaticMethod(nbt.getString("validator"), classOf[ItemStack], classOf[Int], classOf[ItemStack])) else None
     new Slot(kind, tier, validator)
   }
diff --git a/src/main/scala/li/cil/oc/common/template/RobotTemplate.scala b/src/main/scala/li/cil/oc/common/template/RobotTemplate.scala
index 9622397b4..e0f3c07cf 100644
--- a/src/main/scala/li/cil/oc/common/template/RobotTemplate.scala
+++ b/src/main/scala/li/cil/oc/common/template/RobotTemplate.scala
@@ -251,7 +251,7 @@ object RobotTemplate {
   })
 
   private def hasFileSystem(inventory: IInventory) = exists(inventory, stack => Option(api.Driver.driverFor(stack)) match {
-    case Some(driver) => Slot.fromApi(driver.slot(stack)) == Slot.Floppy || Slot.fromApi(driver.slot(stack)) == Slot.HDD
+    case Some(driver) => Slot(driver, stack) == Slot.Floppy || Slot(driver, stack) == Slot.HDD
     case _ => false
   })
 
diff --git a/src/main/scala/li/cil/oc/common/tileentity/Case.scala b/src/main/scala/li/cil/oc/common/tileentity/Case.scala
index c9661e376..90146ffa7 100644
--- a/src/main/scala/li/cil/oc/common/tileentity/Case.scala
+++ b/src/main/scala/li/cil/oc/common/tileentity/Case.scala
@@ -60,7 +60,7 @@ class Case(var tier: Int) extends traits.PowerAcceptor with traits.Computer with
 
   def hasCPU = items.exists {
     case Some(stack) => Option(Driver.driverFor(stack)) match {
-      case Some(driver) => Slot.fromApi(driver.slot(stack)) == Slot.CPU
+      case Some(driver) => Slot(driver, stack) == Slot.CPU
       case _ => false
     }
     case _ => false
@@ -125,6 +125,6 @@ class Case(var tier: Int) extends traits.PowerAcceptor with traits.Computer with
   override def isItemValidForSlot(slot: Int, stack: ItemStack) =
     Option(Driver.driverFor(stack)).fold(false)(driver => {
       val provided = InventorySlots.computer(tier)(slot)
-      Slot.fromApi(driver.slot(stack)) == provided.slot && driver.tier(stack) <= provided.tier
+      Slot(driver, stack) == provided.slot && driver.tier(stack) <= provided.tier
     })
 }
\ No newline at end of file
diff --git a/src/main/scala/li/cil/oc/common/tileentity/DiskDrive.scala b/src/main/scala/li/cil/oc/common/tileentity/DiskDrive.scala
index ab0d40637..0473b2e2b 100644
--- a/src/main/scala/li/cil/oc/common/tileentity/DiskDrive.scala
+++ b/src/main/scala/li/cil/oc/common/tileentity/DiskDrive.scala
@@ -29,7 +29,7 @@ class DiskDrive extends traits.Environment with traits.ComponentInventory with t
   override def getSizeInventory = 1
 
   override def isItemValidForSlot(slot: Int, stack: ItemStack) = (slot, Option(Driver.driverFor(stack))) match {
-    case (0, Some(driver)) => Slot.fromApi(driver.slot(stack)) == Slot.Floppy
+    case (0, Some(driver)) => Slot(driver, stack) == Slot.Floppy
     case _ => false
   }
 
diff --git a/src/main/scala/li/cil/oc/common/tileentity/Robot.scala b/src/main/scala/li/cil/oc/common/tileentity/Robot.scala
index ca6bedd2a..79290b6ba 100644
--- a/src/main/scala/li/cil/oc/common/tileentity/Robot.scala
+++ b/src/main/scala/li/cil/oc/common/tileentity/Robot.scala
@@ -492,7 +492,7 @@ class Robot extends traits.Computer with traits.PowerInformation with api.machin
   def containerSlotType(slot: Int) = if (containerSlots contains slot) {
     val stack = info.containers(slot - 1)
     Option(Driver.driverFor(stack)) match {
-      case Some(driver: api.driver.UpgradeContainer) => Slot.fromApi(driver.providedSlot(stack))
+      case Some(driver: api.driver.UpgradeContainer) => Slot(driver, stack, Some(driver.providedSlot))
       case _ => Slot.None
     }
   }
@@ -515,7 +515,7 @@ class Robot extends traits.Computer with traits.PowerInformation with api.machin
 
   def isFloppySlot(slot: Int) = isComponentSlot(slot) && (Option(getStackInSlot(slot)) match {
     case Some(stack) => Option(Driver.driverFor(stack)) match {
-      case Some(driver) => Slot.fromApi(driver.slot(stack)) == Slot.Floppy
+      case Some(driver) => Slot(driver, stack) == Slot.Floppy
       case _ => false
     }
     case _ => false
@@ -622,7 +622,7 @@ class Robot extends traits.Computer with traits.PowerInformation with api.machin
       // logic making the differentiation of assembler and containers generic.
       driver != server.driver.item.Screen &&
         driver != server.driver.item.Keyboard &&
-        Slot.fromApi(driver.slot(stack)) == containerSlotType(i) &&
+        Slot(driver, stack) == containerSlotType(i) &&
         driver.tier(stack) <= containerSlotTier(i)
     case (i, _) if isInventorySlot(i) => true // Normal inventory.
     case _ => false // Invalid slot.
diff --git a/src/main/scala/li/cil/oc/common/tileentity/Switch.scala b/src/main/scala/li/cil/oc/common/tileentity/Switch.scala
index 503149c91..774b34256 100644
--- a/src/main/scala/li/cil/oc/common/tileentity/Switch.scala
+++ b/src/main/scala/li/cil/oc/common/tileentity/Switch.scala
@@ -157,14 +157,14 @@ class Switch extends traits.Hub with traits.NotAnalyzable with IPeripheral with
 
   private def updateLimits(slot: Int, stack: ItemStack) {
     Driver.driverFor(stack) match {
-      case driver if Slot.fromApi(driver.slot(stack)) == Slot.CPU =>
+      case driver if Slot(driver, stack) == Slot.CPU =>
         relayDelay = math.max(1, relayBaseDelay - ((driver.tier(stack) + 1) * relayDelayPerUpgrade))
-      case driver if Slot.fromApi(driver.slot(stack)) == Slot.Memory =>
+      case driver if Slot(driver, stack) == Slot.Memory =>
         relayAmount = math.max(1, relayBaseAmount + (Items.multi.subItem(stack) match {
           case Some(ram: item.Memory) => (ram.tier + 1) * relayAmountPerUpgrade
           case _ => (driver.tier(stack) + 1) * (relayAmountPerUpgrade * 2)
         }))
-      case driver if Slot.fromApi(driver.slot(stack)) == Slot.HDD =>
+      case driver if Slot(driver, stack) == Slot.HDD =>
         maxQueueSize = math.max(1, queueBaseSize + (driver.tier(stack) + 1) * queueSizePerUpgrade)
     }
   }
@@ -172,9 +172,9 @@ class Switch extends traits.Hub with traits.NotAnalyzable with IPeripheral with
   override protected def onItemRemoved(slot: Int, stack: ItemStack) {
     super.onItemRemoved(slot, stack)
     Driver.driverFor(stack) match {
-      case driver if Slot.fromApi(driver.slot(stack)) == Slot.CPU => relayDelay = relayBaseDelay
-      case driver if Slot.fromApi(driver.slot(stack)) == Slot.Memory => relayAmount = relayBaseAmount
-      case driver if Slot.fromApi(driver.slot(stack)) == Slot.HDD => maxQueueSize = queueBaseSize
+      case driver if Slot(driver, stack) == Slot.CPU => relayDelay = relayBaseDelay
+      case driver if Slot(driver, stack) == Slot.Memory => relayAmount = relayBaseAmount
+      case driver if Slot(driver, stack) == Slot.HDD => maxQueueSize = queueBaseSize
     }
   }
 
@@ -183,7 +183,7 @@ class Switch extends traits.Hub with traits.NotAnalyzable with IPeripheral with
   override def isItemValidForSlot(slot: Int, stack: ItemStack) =
     Option(Driver.driverFor(stack)).fold(false)(driver => {
       val provided = InventorySlots.switch(slot)
-      Slot.fromApi(driver.slot(stack)) == provided.slot && driver.tier(stack) <= provided.tier
+      Slot(driver, stack) == provided.slot && driver.tier(stack) <= provided.tier
     })
 
   // ----------------------------------------------------------------------- //
diff --git a/src/main/scala/li/cil/oc/server/component/Server.scala b/src/main/scala/li/cil/oc/server/component/Server.scala
index a5829c16c..3649535a1 100644
--- a/src/main/scala/li/cil/oc/server/component/Server.scala
+++ b/src/main/scala/li/cil/oc/server/component/Server.scala
@@ -58,7 +58,7 @@ class Server(val rack: tileentity.ServerRack, val number: Int) extends Owner {
 
   def hasCPU = inventory.items.exists {
     case Some(stack) => Option(Driver.driverFor(stack)) match {
-      case Some(driver) => Slot.fromApi(driver.slot(stack)) == Slot.CPU
+      case Some(driver) => Slot(driver, stack) == Slot.CPU
       case _ => false
     }
     case _ => false