title: What is the role of DC bit in GDT?
body: <p>this is my code :</p>
  
  <pre><code>...
  data_seg equ os_data-gdt_start
  code_seg equ os_code-gdt_start
  ...
  jmp code_seg:pm_start
  [BITS 32]
  pm_start:        
  mov ax,data_seg
  mov ds,ax
  mov word [ds:0xb8000],0xC341
  </code></pre>
  
  <p>it work correctly when dc bit (Third bit of Access byte) in the gdt is zero.
  I want to know why not work when it is 1?</p>
  
  <p>I know that dc bit is Direction bit of data selectors , and when it's 0 , the segment grows up and when it's 1 the segment grows down. but not know what is the meaning of grows up and grows down exactly. grows up and grows down means to me when I want to use the stack.( ESP++ and ESP-- )</p>