DATA SEGMENT
STRING1 DB 01H,02H,03H,04H,05H
STRING2 DB 4 DUP(0)
DATA ENDS

CODE SEGMENT
ASSUME CS:CODE,DS:DATA
START: MOV AX,DATA
MOV DS,AX
MOV ES,AX
LEA SI,STRING1
LEA DI,STRING2
MOV CX,05H
CLD
REP MOVSB
INT 3
CODE ENDS
END START

Output

C:\TASM>masm bt.asm
Microsoft (R) Macro Assembler Version 5.00
Copyright (C) Microsoft Corp 1981-1985, 1987.  All rights reserved.

Object filename [bt.OBJ]:
Source listing  [NUL.LST]:
Cross-reference [NUL.CRF]:
bt.asm(1): warning A4001: Extra characters on line

  50422 + 450234 Bytes symbol space free

      1 Warning Errors
      0 Severe  Errors

C:\TASM>link bt.obj
Microsoft (R) Overlay Linker  Version 3.60
Copyright (C) Microsoft Corp 1983-1987.  All rights reserved.

Run File [BT.EXE]:
List File [NUL.MAP]:
Libraries [.LIB]:
LINK : warning L4021: no stack segment

C:\TASM>debug bt.exe
-g

AX=0B97  BX=0000  CX=0000  DX=0000  SP=0000  BP=0000  SI=0005  DI=000A
DS=0B97  ES=0B97  SS=0B97  CS=0B98  IP=0015   NV UP EI PL NZ NA PO NC
0B98:0015 CC            INT     3
-d 0B97:0000
0B97:0000  01 02 03 04 05 01 02 03-04 05 00 00 00 00 00 00   ................
0B97:0010  B8 97 0B 8E D8 8E C0 8D-36 00 00 8D 3E 05 00 B9   ........6...>...
0B97:0020  05 00 FC F3 A4 CC 15 8A-86 70 FF 2A E4 50 B8 FD   .........p.*.P..
0B97:0030  05 50 FF 36 24 21 E8 77-63 83 C4 06 FF 36 24 21   .P.6$!.wc....6$!
0B97:0040  B8 0A 00 50 E8 47 5E 83-C4 04 5E 8B E5 5D C3 90   ...P.G^...^..]..
0B97:0050  55 8B EC 81 EC 84 00 C4-5E 04 26 80 7F 0A 00 74   U.......^.&....t
0B97:0060  3E 8B 46 08 8B 56 0A 89-46 FC 89 56 FE C4 5E FC   >.F..V..F..V..^.
0B97:0070  26 8A 47 0C 2A E4 40 50-8B C3 05 0C 00 52 50 E8   &.G.*[email protected].
-q

C:\TASM>