diff --git a/dos/main.k b/dos/main.k
index ecbb58d..1abc656 100644
--- a/dos/main.k
+++ b/dos/main.k
@@ -24,6 +24,10 @@ main:
     mov ax1, 10
     call print_n
 
+    mov ax0, .buf
+    mov ax1, .msg
+    call strcmp
+
     leave
     ret
 
diff --git a/dos/str/strcmp.k b/dos/str/strcmp.k
new file mode 100644
index 0000000..c2f2457
--- /dev/null
+++ b/dos/str/strcmp.k
@@ -0,0 +1,52 @@
+; The OS/K Team licenses this file to you under the MIT license.
+; See the LICENSE file in the project root for more information.
+
+;
+; int strcmp(const char *str1, const char *str2)
+;
+; Returns:
+;    0 if the contents of both strings are equal
+;    1 if the first character that does not match has a greater value in str1 than in str2
+;   -1 if the first character that does not match has a lower value in str1 than in str2
+;
+
+strcmp:
+    cmp b[ax0], b[ax1]
+    cjmpnz .1
+
+    test b[ax0], b[ax0]
+    cjmpz .1
+
+    inc ax0
+    inc ax1
+    jmp strcmp
+
+.1:
+    mov rax, b[ax0]
+    sub rax, b[ax1]
+    sgn rax, rax
+    ret
+
+;
+; int strncmp(const char *str1, const char *str2, int maxn)
+;
+strncmp:
+    mov rcx, ax2
+
+.1:
+    cmp b[ax0], b[ax1]
+    cjmpnz .1
+
+    test b[ax0], b[ax0]
+    cjmpz .1
+
+    inc ax0
+    inc ax1
+    loop strcmp
+
+.1:
+    mov rax, b[ax0]
+    sub rax, b[ax1]
+    sgn rax, rax
+    ret
+
diff --git a/dos/str/string.k b/dos/str/string.k
index 2e73c55..866140c 100644
--- a/dos/str/string.k
+++ b/dos/str/string.k
@@ -4,4 +4,5 @@
 include "str/strlen.k"
 include "str/strrev.k"
 include "str/strcpy.k"
+include "str/strcmp.k"
 
diff --git a/pc/instrs/INSTRS b/pc/instrs/INSTRS
index 5b935e4..f5729ae 100644
--- a/pc/instrs/INSTRS
+++ b/pc/instrs/INSTRS
@@ -200,6 +200,27 @@ cdecz m
 cdecnz r
 cdecnz m
 
+sgn r r
+sgn r i
+sgn r m
+sgn m r
+sgn m i
+sgn m m
+
+csgnz r r
+csgnz r i
+csgnz r m
+csgnz m r
+csgnz m i
+csgnz m m
+
+csgnnz r r
+csgnnz r i
+csgnnz r m
+csgnnz m r
+csgnnz m i
+csgnnz m m
+
 #
 # Comparison instruction
 #
diff --git a/pc/instrs/arith.c b/pc/instrs/arith.c
index c249253..5cac01b 100644
--- a/pc/instrs/arith.c
+++ b/pc/instrs/arith.c
@@ -10,6 +10,7 @@ IMPL_COND(add);
 IMPL_COND(sub);
 IMPL_COND(mul);
 IMPL_COND(div);
+IMPL_COND(sgn);
 
 //
 // Unsigned arithmetic instructions
@@ -72,3 +73,9 @@ IMPL_START_1(dec)
 }
 IMPL_OUT;
 
+IMPL_START_2(sgn)
+{
+    v1 = (v2 ? ((long)v2 > 0 ? 1 : (ulong)-1L) : 0);
+}
+IMPL_OUT;
+