Added further comments

README.md

@@ -10,10 +10,12 @@ https://github.com/nanochess
 
 This is a port of the amazing Ray Tracer in Atari 8-bit BASIC by D. Scott Williamson. You can see it at [https://bunsen.itch.io/raytrace-movie-atari-8bit-by-d-scott-williamson](https://bunsen.itch.io/raytrace-movie-atari-8bit-by-d-scott-williamson) in turn based on a static BBC micro version by @coprolite9000 [https://bbcmic.ro/?t=9ctpk](https://bbcmic.ro/?t=9ctpk)
 
-I asked him for permission to make a port to a boot sector, and here it is.
+I asked Williamson for permission to make a port to a boot sector, and here it is. I was running around 590 bytes until I found a duplicated calculation that could be made into a subroutine. The code isn't exactly the same because I changed some constants to adapt it, and also collapsed some to save bytes. Anyway, I'm pretty happy I finally found good use for the VGA palette!
 
 If you are going to run it in real hardware it requires a minimum of a Pentium Pro, otherwise most modern emulators will be able to run it.
 
+One of the biggest surprises is how so fast are modern computers so technically the animation is real-time in my Macbook Air running the ray tracer in Windows XP under VirtualBox. You can see it on [Youtube](https://www.youtube.com/watch?v=AZdzECF2Huw).
+
 ### How to use it.
 
 If you want to assemble it, you must download the Netwide Assembler (NASM) from www.nasm.us

ray.asm

@@ -35,17 +35,17 @@ com_file: equ 0
  org 0x7c00 ; Start address for boot sector
  %endif
 
- mov ax,0x0013
- int 0x10
+ mov ax,0x0013 ; Video mode 320x200x256 colors
+ int 0x10 ; Call BIOS.
 
- sub sp,total
- mov bp,sp
+ sub sp,total ; Make space for internal variables.
+ mov bp,sp ; Use BP to refer them.
 
- mov ax,0xa000
+ mov ax,0xa000 ; Point to video RAM.
  mov es,ax
 
- finit
- cld
+ finit ; Reset coprocessor.
+ cld ; Clear direction flag.
 restart:
  fld dword [const_25] ; Initial viewpoint (z)
  fstp dword [bp+var_a] ; a = 25.0