diff --git a/core/mem.c b/core/mem.c
index 8e1bdc7..685fddd 100644
--- a/core/mem.c
+++ b/core/mem.c
@@ -34,7 +34,7 @@ int memSetup(unsigned long upper_mem)
 	return 0;
 }
 
-struct mem_desc *addr2memDesc(unsigned long addr)
+struct mem_desc *addr2memDesc(paddr_t addr)
 {
 	if (addr > top_mem || addr < bottom_mem)
 		return NULL;
@@ -43,7 +43,7 @@ struct mem_desc *addr2memDesc(unsigned long addr)
 	return page_desc + idx;
 }
 
-unsigned long allocPhyPage(void)
+paddr_t allocPhyPage(void)
 {
 	if (list_is_empty(free_page)) {
 		return (unsigned long)NULL;
@@ -54,7 +54,7 @@ unsigned long allocPhyPage(void)
 	return mem->phy_addr;
 }
 
-int unrefPhyPage(unsigned long addr)
+int unrefPhyPage(paddr_t addr)
 {
 	struct mem_desc *mem = addr2memDesc(addr);
 	if (!mem) {
@@ -69,7 +69,7 @@ int unrefPhyPage(unsigned long addr)
 	return 0;
 }
 
-int refPhyPage(unsigned long addr)
+int refPhyPage(paddr_t addr)
 {
 	struct mem_desc *mem = addr2memDesc(addr);
 	if (!mem) {
diff --git a/core/mem.h b/core/mem.h
index 1249c0d..bdba9f8 100644
--- a/core/mem.h
+++ b/core/mem.h
@@ -1,4 +1,5 @@
 #pragma once
+#include "types.h"
 #include "stdarg.h"
 
 
@@ -10,13 +11,13 @@ extern uint32_t __ld_kernel_begin;
 extern uint32_t __ld_kernel_end;
 
 struct mem_desc{
-	unsigned long phy_addr;
+	paddr_t phy_addr;
 	unsigned long ref;
 	struct mem_desc *next, *prev;
 };
 
 
 int memSetup(unsigned long upper_mem);
-unsigned long allocPhyPage(void);
-int unrefPhyPage(unsigned long addr);
-int refPhyPage(unsigned long addr);
+paddr_t allocPhyPage(void);
+int unrefPhyPage(paddr_t addr);
+int refPhyPage(paddr_t addr);
diff --git a/core/types.h b/core/types.h
new file mode 100644
index 0000000..44b9fca
--- /dev/null
+++ b/core/types.h
@@ -0,0 +1,7 @@
+#pragma once
+
+// Virtual address
+typedef unsigned long vaddr_t;
+
+// Physical address
+typedef unsigned long paddr_t;