diff --git a/ide.c b/ide.c
index 3b3b808..83bffcf 100644
--- a/ide.c
+++ b/ide.c
@@ -26,20 +26,16 @@ static struct spinlock ide_lock;
 static struct buf *ide_queue;
 
 static int disk_1_present;
-
-static int ide_probe_disk1(void);
 static void ide_start_request();
 
-//PAGEBREAK: 10
 // Wait for IDE disk to become ready.
 static int
 ide_wait_ready(int check_error)
 {
   int r;
 
-  while(((r = inb(0x1F7)) & (IDE_BSY|IDE_DRDY)) != IDE_DRDY)
+  while(((r = inb(0x1f7)) & IDE_BSY) || !(r & IDE_DRDY))
     ;
-
   if(check_error && (r & (IDE_DF|IDE_ERR)) != 0)
     return -1;
   return 0;
@@ -48,105 +44,103 @@ ide_wait_ready(int check_error)
 void
 ide_init(void)
 {
+  int i;
+
   initlock(&ide_lock, "ide");
   irq_enable(IRQ_IDE);
   ioapic_enable(IRQ_IDE, ncpu - 1);
   ide_wait_ready(0);
-  disk_1_present = ide_probe_disk1();
+  
+  // Check if disk 1 is present
+  outb(0x1f6, 0xE0 | (1<<4));
+  for(i=0; i<1000; i++){
+    if(inb(0x1f7) != 0){
+      disk_1_present = 1;
+      break;
+    }
+  }
+  
+  // Switch back to disk 0.
+  outb(0x1f6, 0xE0 | (0<<4));
 }
 
-// Probe to see if disk 1 exists (we assume disk 0 exists).
-static int
-ide_probe_disk1(void)
+// Start the request for b.  Caller must hold ide_lock.
+static void
+ide_start_request(struct buf *b)
 {
-  int r, x;
+  if(b == 0)
+    panic("ide_start_request");
 
-  // wait for Device 0 to be ready
   ide_wait_ready(0);
-
-  // switch to Device 1
-  outb(0x1F6, 0xE0 | (1<<4));
-
-  // check for Device 1 to be ready for a while
-  for(x = 0; x < 1000 && (r = inb(0x1F7)) == 0; x++)
-    ;
-
-  // switch back to Device 0
-  outb(0x1F6, 0xE0 | (0<<4));
-
-  return x < 1000;
+  outb(0x3f6, 0);  // generate interrupt
+  outb(0x1f2, 1);  // number of sectors
+  outb(0x1f3, b->sector & 0xff);
+  outb(0x1f4, (b->sector >> 8) & 0xff);
+  outb(0x1f5, (b->sector >> 16) & 0xff);
+  outb(0x1f6, 0xE0 | ((b->dev&1)<<4) | ((b->sector>>24)&0x0f));
+  if(b->flags & B_WRITE){
+    outb(0x1f7, IDE_CMD_WRITE);
+    outsl(0x1f0, b->data, 512/4);
+  }else{
+    outb(0x1f7, IDE_CMD_READ);
+  }
 }
 
-// Interrupt handler - wake up the request that just finished.
+// Interrupt handler.
 void
 ide_intr(void)
 {
+  struct buf *b;
+
   acquire(&ide_lock);
-  if(ide_queue){
-    if((ide_queue->flags & B_WRITE) == 0)
-      if(ide_wait_ready(1) >= 0)
-        insl(0x1F0, ide_queue->data, 512/4);
-    ide_queue->done = 1;
-    wakeup(ide_queue);
-    ide_queue = ide_queue->qnext;
-    ide_start_request();
-  } else {
+  if((b = ide_queue) == 0){
     cprintf("stray ide interrupt\n");
+    release(&ide_lock);
+    return;
   }
+
+  // Read data if needed.
+  if((b->flags & B_WRITE) == 0 && ide_wait_ready(1) >= 0)
+    insl(0x1f0, b->data, 512/4);
+  
+  // Wake process waiting for this buf.
+  b->done = 1;
+  wakeup(b);
+  
+  // Start disk on next buf in queue.
+  if((ide_queue = b->qnext) != 0)
+    ide_start_request(ide_queue);
+
   release(&ide_lock);
 }
 
-// Start the next request in the queue.
-// Caller must hold ide_lock.
-static void
-ide_start_request (void)
-{
-  if(ide_queue){
-    ide_wait_ready(0);
-    outb(0x3f6, 0);  // generate interrupt
-    outb(0x1F2, 1);  // number of sectors
-    outb(0x1F3, ide_queue->sector & 0xFF);
-    outb(0x1F4, (ide_queue->sector >> 8) & 0xFF);
-    outb(0x1F5, (ide_queue->sector >> 16) & 0xFF);
-    outb(0x1F6, 0xE0 |
-         ((ide_queue->dev & 1)<<4) |
-         ((ide_queue->sector>>24)&0x0F));
-    if(ide_queue->flags & B_WRITE){
-      outb(0x1F7, IDE_CMD_WRITE);
-      outsl(0x1F0, ide_queue->data, 512/4);
-    } else {
-      outb(0x1F7, IDE_CMD_READ);
-    }
-  }
-}
-
-//PAGEBREAK: 30
-// Queue up a disk operation and wait for it to finish.
-// b must have B_BUSY set.
+//PAGEBREAK!
+// Queue a disk operation and wait for it to finish.
 void
 ide_rw(struct buf *b)
 {
   struct buf **pp;
 
-  if((b->dev & 0xff) && !disk_1_present)
+  if(!(b->flags & B_BUSY))
+    panic("ide_rw: buf not busy");
+  if(b->dev != 0 && !disk_1_present)
     panic("ide disk 1 not present");
 
   acquire(&ide_lock);
 
+  // Append b to ide_queue.
   b->done = 0;
   b->qnext = 0;
-
-  // append b to ide_queue
-  pp = &ide_queue;
-  while(*pp)
-    pp = &(*pp)->qnext;
+  for(pp=&ide_queue; *pp; pp=&(*pp)->qnext)
+    ;
   *pp = b;
   
+  // Start disk if necessary.
   if(ide_queue == b)
-    ide_start_request();
+    ide_start_request(b);
   
+  // Wait for request to finish.
   while(!b->done)
     sleep(b, &ide_lock);
-  
   release(&ide_lock);
 }