Write an 8086 Assembly Language Program to transfer a block of 50 bytes from a source array starting at memory offset 3000H to a destination. You must use loop instructions (LOOP or REP) and appropriate string instructions (St, DI). Provide detailed comments explaining each line of code.

.MODEL SMALL        ; Defines the memory model as small (code and data in one segment)
.STACK 100H         ; Reserves 100H bytes for the stack

.DATA               ; Data segment definition (optional, but good practice)
    ; No explicit variables defined here as source/destination are at specific offsets.
    ; We assume the source array starts at DS:3000H and destination at ES:4000H.

.CODE               ; Code segment definition
MAIN PROC           ; Start of the main procedure

    ; Initialize Data Segment (DS) and Extra Segment (ES)
    ; Both DS and ES are set to the current data segment.
    ; This assumes both source and destination arrays reside within the same segment.
    MOV AX, @DATA       ; Load the address of the data segment into AX
    MOV DS, AX          ; Set DS to point to the data segment
    MOV ES, AX          ; Set ES to point to the data segment (for destination)

    ; Initialize Source Index (SI) and Destination Index (DI)
    MOV SI, 3000H       ; SI points to the starting offset of the source array (DS:3000H)
    MOV DI, 4000H       ; DI points to the starting offset of the destination array (ES:4000H)

    ; Set the count for the number of bytes to transfer
    MOV CX, 50          ; Set CX register to 50 (decimal) for 50 bytes to transfer

    ; Set Direction Flag (DF) for auto-increment
    CLD                 ; Clear Direction Flag (DF=0). This ensures that SI and DI
                        ; will be incremented after each byte transfer, moving
                        ; from lower addresses to higher addresses.

    ; Perform the block transfer using REP MOVSB
    REP MOVSB           ; The REP prefix repeats the MOVSB (Move String Byte) instruction
                        ; CX times.
                        ; MOVSB performs the following actions:
                        ; 1. Moves a byte from memory location [DS:SI] to [ES:DI].
                        ; 2. Increments SI by 1 (since DF=0).
                        ; 3. Increments DI by 1 (since DF=0).
                        ; 4. Decrements CX by 1.
                        ; The REP prefix continues this loop until CX becomes zero.

    ; Program termination
    MOV AH, 4CH         ; Load function code 4CH into AH (Terminate Program)
    INT 21H             ; Call DOS interrupt to terminate the program

MAIN ENDP           ; End of the main procedure
END MAIN            ; End of the program, specifying the entry point