diff --git a/Makefile b/Makefile
index c6360fd..4324d1c 100644
--- a/Makefile
+++ b/Makefile
@@ -129,7 +129,6 @@ UPROGS=\
 	$U/_usertests\
 	$U/_wc\
 	$U/_zombie\
-	$U/_cow\
 
 fs.img: mkfs/mkfs README $(UPROGS)
 	mkfs/mkfs fs.img README $(UPROGS)
diff --git a/user/cow.c b/user/cow.c
deleted file mode 100644
index 0426600..0000000
--- a/user/cow.c
+++ /dev/null
@@ -1,196 +0,0 @@
-//
-// tests for copy-on-write fork() assignment.
-//
-
-#include "kernel/types.h"
-#include "kernel/memlayout.h"
-#include "user/user.h"
-
-// allocate more than half of physical memory,
-// then fork. this will fail in the default
-// kernel, which does not support copy-on-write.
-void
-simpletest()
-{
-  uint64 phys_size = PHYSTOP - KERNBASE;
-  int sz = (phys_size / 3) * 2;
-
-  printf(1, "simple: ");
-  
-  char *p = sbrk(sz);
-  if(p == (char*)0xffffffffffffffffL){
-    printf(1, "sbrk(%d) failed\n", sz);
-    exit();
-  }
-
-  for(char *q = p; q < p + sz; q += 4096){
-    *(int*)q = getpid();
-  }
-
-  int pid = fork();
-  if(pid < 0){
-    printf(1, "fork() failed\n");
-    exit();
-  }
-
-  if(pid == 0)
-    exit();
-
-  wait();
-
-  if(sbrk(-sz) == (char*)0xffffffffffffffffL){
-    printf(1, "sbrk(-%d) failed\n", sz);
-    exit();
-  }
-
-  printf(1, "ok\n");
-}
-
-// three processes all write COW memory.
-// this causes more than half of physical memory
-// to be allocated, so it also checks whether
-// copied pages are freed.
-void
-threetest()
-{
-  uint64 phys_size = PHYSTOP - KERNBASE;
-  int sz = phys_size / 4;
-  int pid1, pid2;
-
-  printf(1, "three: ");
-  
-  char *p = sbrk(sz);
-  if(p == (char*)0xffffffffffffffffL){
-    printf(1, "sbrk(%d) failed\n", sz);
-    exit();
-  }
-
-  pid1 = fork();
-  if(pid1 < 0){
-    printf(1, "fork failed\n");
-    exit();
-  }
-  if(pid1 == 0){
-    pid2 = fork();
-    if(pid2 < 0){
-      printf(1, "fork failed");
-      exit();
-    }
-    if(pid2 == 0){
-      for(char *q = p; q < p + (sz/5)*4; q += 4096){
-        *(int*)q = getpid();
-      }
-      for(char *q = p; q < p + (sz/5)*4; q += 4096){
-        if(*(int*)q != getpid()){
-          printf(1, "wrong content\n");
-          exit();
-        }
-      }
-      exit();
-    }
-    for(char *q = p; q < p + (sz/2); q += 4096){
-      *(int*)q = 9999;
-    }
-    exit();
-  }
-
-  for(char *q = p; q < p + sz; q += 4096){
-    *(int*)q = getpid();
-  }
-
-  wait();
-
-  sleep(1);
-
-  for(char *q = p; q < p + sz; q += 4096){
-    if(*(int*)q != getpid()){
-      printf(1, "wrong content\n");
-      exit();
-    }
-  }
-
-  if(sbrk(-sz) == (char*)0xffffffffffffffffL){
-    printf(1, "sbrk(-%d) failed\n", sz);
-    exit();
-  }
-
-  printf(1, "ok\n");
-}
-
-char junk1[4096];
-int fds[2];
-char junk2[4096];
-char buf[4096];
-char junk3[4096];
-
-// test whether copyout() simulates COW faults.
-void
-filetest()
-{
-  int parent = getpid();
-  
-  printf(1, "file: ");
-  
-  buf[0] = 99;
-
-  for(int i = 0; i < 4; i++){
-    if(pipe(fds) != 0){
-      printf(1, "pipe() failed\n");
-      exit();
-    }
-    int pid = fork();
-    if(pid < 0){
-      printf(1, "fork failed\n");
-      exit();
-    }
-    if(pid == 0){
-      sleep(1);
-      if(read(fds[0], buf, sizeof(i)) != sizeof(i)){
-        printf(1, "read failed\n");
-        kill(parent);
-        exit();
-      }
-      sleep(1);
-      int j = *(int*)buf;
-      if(j != i){
-        printf(1, "read the wrong value\n");
-        kill(parent);
-        exit();
-      }
-      exit();
-    }
-    if(write(fds[1], &i, sizeof(i)) != sizeof(i)){
-      printf(1, "write failed\n");
-      exit();
-    }
-  }
-
-  for(int i = 0; i < 4; i++)
-    wait();
-
-  if(buf[0] != 99){
-    printf(1, "child overwrote parent\n");
-    exit();
-  }
-
-  printf(1, "ok\n");
-}
-
-int
-main(int argc, char *argv[])
-{
-  simpletest();
-
-  // check that the first simpletest() freed the physical memory.
-  simpletest();
-
-  threetest();
-  threetest();
-  threetest();
-
-  filetest();
-
-  printf(1, "ALL COW TESTS PASSED\n");
-
-  exit();
-}