Use backtick code blocks for syntax highlighting

04-02.md

@@ -53,11 +53,15 @@ byte-sized accesses. That's why the official instruction timings
 indicate that for code running on an 8088 an additional 4 cycles are
 required for every word-sized access to a memory operand. For instance,
 
-    mov  ax,word ptr [MemVar]
+```nasm
+mov  ax,word ptr [MemVar]
+```
 
 takes 4 cycles longer to read the word at address **MemVar** than
 
-    mov  al,byte ptr [MemVar]
+```nasm
+mov  al,byte ptr [MemVar]
+```
 
 takes to read the byte at address **MemVar.** (Actually, the difference
 between the two isn't very likely to be exactly 4 cycles, for reasons
@@ -72,11 +76,15 @@ prior to adding to it, and one to write the result of the addition back
 to the destination operand—and thus incurs not one but two 4-cycle
 penalties. As a result
 
-    add  word ptr [MemVar],ax
+```nasm
+add  word ptr [MemVar],ax
+```
 
 takes about 8 cycles longer to execute than:
 
-    add  byte ptr [MemVar],al
+```nasm
+add  byte ptr [MemVar],al
+```
 
 String instructions can suffer from the 8-bit bus cycle-eater to a
 greater extent than other instructions. Believe it or not, a single
@@ -114,35 +122,39 @@ in all.
 
 **LISTING 4.1 LST4-1.ASM**
 
-    ; Measures the performance of a loop which uses a
-    ; byte-sized memory variable as the loop counter.
-    ;
-          jmp  Skip
-    ;
-    Counter    db    100
-    ;
-    Skip:
-          call ZTimerOn
-    LoopTop:
-          dec  [Counter]
-          jnz  LoopTop
-          call ZTimerOff
+```nasm
+; Measures the performance of a loop which uses a
+; byte-sized memory variable as the loop counter.
+;
+      jmp  Skip
+;
+Counter    db    100
+;
+Skip:
+      call ZTimerOn
+LoopTop:
+      dec  [Counter]
+      jnz  LoopTop
+      call ZTimerOff
+```
 
 **LISTING 4.2 LST4-2.ASM**
 
-    ; Measures the performance of a loop which uses a
-    ; word-sized memory variable as the loop counter.
-    ;
-          jmp  Skip
-    ;
-    Counter    dw    100
-    ;
-    Skip:
-          call  ZTimerOn
-    LoopTop:
-          dec   [Counter]
-          jnz   LoopTop
-          call  ZTimerOff
+```nasm
+; Measures the performance of a loop which uses a
+; word-sized memory variable as the loop counter.
+;
+      jmp  Skip
+;
+Counter    dw    100
+;
+Skip:
+      call  ZTimerOn
+LoopTop:
+      dec   [Counter]
+      jnz   LoopTop
+      call  ZTimerOff
+```
 
 I'd like to make a brief aside concerning code optimization in the
 listings in this book. Throughout this book I've modeled the sample code