I have just started studying X86 Assembly Language.
My doubt -
When I am using the DOS DEBUG program to look at memory location, I am getting slightly different values on examining the same memory location using two different segment:offset addresses. I.e.-
Aren't D 40[0]:17 and D 41[0]:7 supposed to give exactly same output? since both of them give same address on adding segment + offset = 400+17 = 410+7 = 417H
The results which I get - (notice they are slightly different)
-D 40:17
0040:0010 00-00 00 1E 00 1E 00 0D 1C .........
0040:0020 44 20 20 39 34 05 34 05-3A 27 39 0A 0D 1C 44 20 D 94.4.:'9...D
0040:0030 20 39 34 05 30 0B 3A 27-31 02 37 08 0D 1C 00 00 94.0.:'1.7.....
0040:0040 93 00 C3 00 00 00 00 00-00 03 50 00 00 10 00 00 ..........P.....
0040:0050 00 18 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0040:0060 0F 0C 00 D4 03 29 30 00-00 00 00 00 91 DA 10 00 .....)0.........
0040:0070 00 00 00 00 00 00 08 00-14 14 14 14 01 01 01 01 ................
0040:0080 1E 00 3E 00 18 10 00 60-F9 11 0B 00 50 01 00 00 ..>....`....P...
0040:0090 00 00 00 00 00 00 10 .......
-D 41:7
0041:0000 00-00 00 2C 00 2C 00 44 20 ...,.,.D
0041:0010 20 39 34 05 31 02 3A 27-37 08 0D 1C 0D 1C 44 20 94.1.:'7.....D
0041:0020 20 39 34 05 30 0B 3A 27-31 02 37 08 0D 1C 00 00 94.0.:'1.7.....
0041:0030 08 00 C3 00 00 00 00 00-00 03 50 00 00 10 00 00 ..........P.....
0041:0040 00 18 00 00 00 00 00 00-00 00 00 00 00 00 00 00 ................
0041:0050 0F 0C 00 D4 03 29 30 00-00 00 00 00 1C DB 10 00 .....)0.........
0041:0060 00 00 00 00 00 00 08 00-14 14 14 14 01 01 01 01 ................
0041:0070 1E 00 3E 00 18 10 00 60-F9 11 0B 00 50 01 00 00 ..>....`....P...
0041:0080 00 00 00 00 00 00 10 .......
You are looking at the BIOS data area, whose contents changes over time since it contains things like the state of shift/control/alt keys, the read/write positions of the keyboard buffer and the timer.