My code

 [org 0x7c00]
 [bits 16]

 init:
   mov [BOOT_DISK], dl
   xor ax, ax
   mov es, ax
   mov ds, ax
   mov bp, 0x8000
   mov sp, bp
   mov bx, KERNEL_LOCATION
   mov dh, 20
   mov ah, 0x02
   mov al, dh
   mov ch, 0x00
   mov dh, 0x00
   mov cl, 0x02
   mov dl, [BOOT_DISK]
   int 0x13
   mov ah, 0x0e
   mov bx, string
   mov si, reserved
   jmp loop

 loop:
   mov al, [bx]
   cmp al, 0
   je key_press
   int 0x10
   inc bx
   jmp loop

 PS1:
   cmp byte [bx], 0
   je go_back_PS1
   mov ah, 0x0e
   mov al, [bx]
   int 0x10
   inc bx
   jmp PS1

 go_back_PS1:
   popa
   jmp key_press

 command_not_found:
   cmp byte [bx], 0
   je go_back_command_not_found
   mov al, [bx]
   int 0x10
   inc bx
   jmp command_not_found

 go_back_command_not_found:
   popa
   pusha
   mov bx, PS1_env
   jmp PS1

 key_press:
   mov ah, 0x00
   int 0x16
   cmp al, 0x21
 ;  mov si, reserved
   jge compare
   jl other_chars
   jmp key_press

 compare:
   cmp al, 0x7e
   jl print
   jmp key_press

 print:
   pusha
   mov ah, 0x0e
   int 0x10
   popa
   mov [si], al
   inc si
   jmp key_press

 other_chars:
   cmp ah, 0x1C
   je enter
   cmp ah, 0x39
   je space
   cmp al, 0x8
   je backspace
   jmp key_press

 enter:
   pusha
   mov ah, 0x0e
   mov al, 0x0a
   int 0x10
   mov al, 0x0d
   int 0x10
   popa
   mov di, reserved
   mov bx, ping_command
   jmp loop1

 loop1:
   cmp di, si
   je middle_loop1
   cmp byte [bx], 0
   je go_back_loop1
   mov ch, [di]
   cmp ch, [bx]
   jne go_back_loop1
 ;  pusha
 ;  mov ah, 0x0e
 ;  mov al, [di]
 ;  int 0x10
 ;  popa
   inc di
   inc bx
   jmp loop1

 go_back_loop1:
   mov si, reserved
   mov bx, ping_command
   pusha
   mov ah, 0x0e
   mov bx, command_not_found_text
   jmp command_not_found
 ;  pusha
 ;  mov bx, PS1_env
 ;  jmp PS1
 ;  jmp key_press

 middle_loop1:
   mov si, reserved
   mov bx, pong
   pusha
   jmp print_ping

 print_ping:
   cmp byte [bx], 0
   je go_back_print_ping
   mov ah, 0x0e
   mov al, [bx]
   int 0x10
   inc bx
   jmp print_ping

 go_back_print_ping:
   mov al, 0x0a
   int 0x10
   mov al, 0x0d
   int 0x10
   jmp enter_PM
 ;  mov bx, PS1_env
 ;  jmp PS1
 ;  popa
 ;  jmp key_press

 space:
   pusha
   mov ah, 0x0e
   mov al, ' '
   int 0x10
   popa
   mov byte [si], ' '
   inc si
   jmp key_press

 backspace:
   cmp si, reserved
   jle key_press
   pusha
   mov ah, 0x0e
   int 0x10
   mov al, ' '
   int 0x10
   mov al, 0x8
   int 0x10
   popa
   dec si
   jmp key_press

 enter_PM:
 ;  mov ah, 0x0
 ;  mov al, 0x3
 ;  int 0x10
   cli
   lidt [IDT_Descriptor]
   lgdt [GDT_Descriptor]
   mov eax, cr0
   or eax, 1
   mov cr0, eax
   jmp CODE_SEG:protected_mode

 [bits 32]
 protected_mode:
 ;  mov byte [0xb8000], 'A'
 ;  jmp halt
   call KERNEL_LOCATION
   jmp halt

 halt:
   hlt
   jmp halt

 GDT_Start:
   null_descriptor:
     dd 0
     dd 0
   code_descriptor:
     dw 0xffff
     dw 0
     db 0
     db 0b10011010
     db 0b11001111
     db 0
   data_descriptor:
     dw 0xffff
     dw 0
     db 0
     db 0b10010010
     db 0b11001111
     db 0
 GDT_End:

 GDT_Descriptor:
   dw GDT_End - GDT_Start - 1
   dd GDT_Start

 IDT_Start:
   KEYBOARD:
     dw 0x0078
     dw CODE_SEG
     db 0
     db 0b11100001
     dw 0x0000
 IDT_End:

 IDT_Descriptor:
   dw IDT_End - IDT_Start - 1
   dd IDT_Start

 CODE_SEG equ code_descriptor - GDT_Start
 DATA_SEG equ data_descriptor - GDT_Start
 KERNEL_LOCATION equ 0x1000
 BOOT_DISK db 0
 ping_command db "ping", 0
 pong db "pong", 0
 PS1_env db "admin% ", 0
 command_not_found_text db "Command not found!", 0xa, 0xd, 0
 string db "It's me! Mario!", 0xa, 0xd, "admin% ", 0
 times 510-($-$$) db 0
 dw 0xAA55
 reserved resb 128