diff --git a/presets/coleco/climber.c b/presets/coleco/climber.c
index 06d6365c..0a96bbd4 100644
--- a/presets/coleco/climber.c
+++ b/presets/coleco/climber.c
@@ -1,4 +1,9 @@
 
+/*
+Demonstration game.
+For more information, see "Making Games for the NES".
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <cv.h>
diff --git a/presets/coleco/cursorsmooth.c b/presets/coleco/cursorsmooth.c
index 41d36d3d..9753d2dc 100644
--- a/presets/coleco/cursorsmooth.c
+++ b/presets/coleco/cursorsmooth.c
@@ -1,4 +1,9 @@
 
+/*
+This demo animates two 16 x 16 sprites.
+It also uses the collision detection bit.
+*/
+
 #include <stdint.h>
 #include <stdlib.h>
 #include <cv.h>
@@ -48,6 +53,10 @@ void move_cursor(struct cvu_sprite *s, int controller) {
   if (cs.joystick & CV_DOWN) y++;
   if (cs.joystick & CV_UP) y--;
 
+  // M;
+
+  // M;
+
   // Make sure cursor doesn't leave the screen.
   if(x < 0) x = 0;
   if(x > 239) x = 239;
diff --git a/presets/coleco/hello.c b/presets/coleco/hello.c
index 8e89fa17..cde05cf1 100644
--- a/presets/coleco/hello.c
+++ b/presets/coleco/hello.c
@@ -1,25 +1,33 @@
 
+/*
+This is a demonstration of integrating the C
+standard I/O (stdio) functions with the display,
+so that standard functions like printf() can be used.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
 #include <cv.h>
 #include <cvu.h>
 
+// overrides value in common.h
 #define COLS 40
 
 #include "common.h"
 //#link "common.c"
 
 void setup_40_column_font() {
-  cv_set_image_table(IMAGE);
-  copy_default_character_set();
-  cv_set_character_pattern_t(PATTERN);
   cv_set_screen_mode(CV_SCREENMODE_TEXT);
+  cv_set_image_table(IMAGE);
+  cv_set_character_pattern_t(PATTERN);
+  copy_default_character_set();
 }
 
-char cursor_x;
-char cursor_y;
+char cursor_x;	// current cursor column
+char cursor_y;	// current cursor row
 
+// clear the screen to ' ' (blank spaces)
 void clrscr() {
   cvu_vmemset(IMAGE, ' ', COLS*ROWS);
 }
@@ -30,6 +38,8 @@ void setup_stdio() {
   clrscr();
 }
 
+// scroll the screen upward, by copying each row
+// of VRAM to its previous row.
 void scrollup() {
   char buf[COLS];
   char y;
@@ -40,6 +50,7 @@ void scrollup() {
   cvu_vmemset(IMAGE + COLS*(ROWS-1), ' ', COLS);
 }
 
+// move cursor to next line, scrolling when it hits the bottom.
 void newline() {
   if (cursor_y >= ROWS-1) {
     scrollup();
@@ -48,15 +59,18 @@ void newline() {
   }
 }
 
+// write a character to the screen.
 int putchar(int ch) {
   switch (ch) {
     case '\n':
-      newline(); // TODO: scrolling
+      newline();	// move cursor to next line
     case '\r':
-      cursor_x = 0;
+      cursor_x = 0;	// move cursor to start of line
       return 0;
   }
+  // output character to VRAM at cursor position
   cvu_voutb(ch, IMAGE + COLS*cursor_y + cursor_x);
+  // move cursor to right, going to next line if neccessary
   cursor_x++;
   if (cursor_x >= COLS) {
     newline();
@@ -64,6 +78,9 @@ int putchar(int ch) {
   }
 }
 
+#ifdef __MAIN__
+
+// test program
 void main() {
   unsigned char byteval = 123;
   signed char charval = 123;
@@ -79,3 +96,5 @@ void main() {
       charval++, byteval++, shortval++);
   }
 }
+
+#endif
diff --git a/presets/coleco/lines.c b/presets/coleco/lines.c
index f5e8950a..0a8b2bd4 100644
--- a/presets/coleco/lines.c
+++ b/presets/coleco/lines.c
@@ -1,4 +1,10 @@
 
+/*
+This demo draws pixels and lines in Mode 2.
+Note that when lines of two different colors overlap,
+they create "clashing" effects.
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <stdio.h>
@@ -54,6 +60,8 @@ void draw_line(int x0, int y0, int x1, int y1, byte color) {
   }
 }
 
+#ifdef _MAIN_
+
 void main() {
   setup_mode2();
   cv_set_screen_active(true);
@@ -61,3 +69,5 @@ void main() {
     draw_line(rand()&0xff, rand()&0xbf, rand()&0xff, rand()&0xbf, rand()&15);
   }
 }
+
+#endif
diff --git a/presets/coleco/mode2bitmap.c b/presets/coleco/mode2bitmap.c
index 18a5aa3b..4a00e1ce 100644
--- a/presets/coleco/mode2bitmap.c
+++ b/presets/coleco/mode2bitmap.c
@@ -1,4 +1,19 @@
 
+/*
+Displays a bitmap using the TMS9928A's Mode 2.
+
+In Mode 2, the screen is horizontally divided into three
+256×64 pixel areas, each of which gets its own character
+set. By sequentially printing the characters 0 through 255
+in all three areas, the program can simulate a graphics mode
+where each pixel can be set individually.
+
+The limitation is that every horizontal run of 8 pixels
+can only have two colors (a foreground and background color.)
+
+The included Mode 2 bitmap was converted with a web utility:
+http://msx.jannone.org/conv/
+*/
 
 #include <stdlib.h>
 
diff --git a/presets/coleco/mode2compressed.c b/presets/coleco/mode2compressed.c
index 32e2c249..83cf825d 100644
--- a/presets/coleco/mode2compressed.c
+++ b/presets/coleco/mode2compressed.c
@@ -1,4 +1,9 @@
 
+/*
+This demo uncompresses the Mode 2 bitmap from a
+compressed LZG stream in ROM. This takes several times
+longer than just copying it from ROM.
+*/
 
 #include <stdlib.h>
 
diff --git a/presets/coleco/multicolor.c b/presets/coleco/multicolor.c
index 8bf6a176..c76e08b8 100644
--- a/presets/coleco/multicolor.c
+++ b/presets/coleco/multicolor.c
@@ -1,5 +1,8 @@
 /*
-64x48 multicolor mode
+Demonstrates the 64x48 multicolor mode.
+This mode is a little tricky to implement,
+but each pixel can have its own color with no
+clashing effects.
 */
 
 #include <stdlib.h>
@@ -58,7 +61,9 @@ void draw_line(int x0, int y0, int x1, int y1, byte color) {
     if (e2 < dy) { err += dx; y0 += sy; }
   }
 }
- 
+
+#ifdef _MAIN_
+
 void main() {
   setup_multicolor();
   cv_set_screen_active(true);
@@ -67,3 +72,5 @@ void main() {
   }
   while (1);
 }
+
+#endif
diff --git a/presets/coleco/musicplayer.c b/presets/coleco/musicplayer.c
index 03a5980d..817c430a 100644
--- a/presets/coleco/musicplayer.c
+++ b/presets/coleco/musicplayer.c
@@ -1,4 +1,11 @@
 
+/*
+Demonstrates playing multi-voice music on the SN76489A PSG
+using the CVLib functions.
+
+Similar to the music example in "Making Arcade Games in C".
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <cv.h>
diff --git a/presets/coleco/shoot.c b/presets/coleco/shoot.c
index 1ab3fa10..34939f4b 100644
--- a/presets/coleco/shoot.c
+++ b/presets/coleco/shoot.c
@@ -1,4 +1,9 @@
 
+/*
+Demonstration game.
+For more information, see "Making Arcade Games in C".
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <cv.h>
diff --git a/presets/coleco/siegegame.c b/presets/coleco/siegegame.c
index 7c615e91..ef0b30ea 100644
--- a/presets/coleco/siegegame.c
+++ b/presets/coleco/siegegame.c
@@ -1,4 +1,9 @@
 
+/*
+Demonstration game.
+For more information, see "Making Arcade Games in C".
+*/
+
 #include <stdlib.h>
 #include <string.h>
 #include <cv.h>
diff --git a/presets/coleco/simplemusic.c b/presets/coleco/simplemusic.c
index 13c97eda..f2ef81ae 100644
--- a/presets/coleco/simplemusic.c
+++ b/presets/coleco/simplemusic.c
@@ -1,4 +1,12 @@
 
+/*
+This demonstrates the cvu_play_music() function.
+Command-line tools generate the music file from ABC source files.
+
+For more information, see:
+http://www.colecovision.eu/ColecoVision/development/tutorial2.shtml
+*/
+
 #include <stdint.h>
 
 const uint16_t notes[] = { 12846, 12334, 11086, 10062, 10062, 9806, 10062, 10574, 11086, 10062, 11086, 12430, 11042, 12334, 12878, 14158, 14158, 12878, 13390, 13646, 10574, 9806, 10574, 12430, 12846, 12334, 11086, 10062, 10062, 9806, 10062, 10574, 11086, 10062, 11086, 12430, 11054, 12334, 12878, 14158, 14158, 12878, 13390, 13646, 10574, 10062, 10062, 10126, 11054, 12334, 12878, 14158, 13902, 14158, 14670, 14158, 13646, 12878, 13390, 13646, 3918, 12878, 14158, 13902, 12878, 12366, 12878, 12366, 12878, 11086, 10062, 9870, 12334, 11054, 11086, 10062, 10062, 9806, 10062, 10574, 11086, 10062, 11086, 12430, 11054, 12334, 12878, 14158, 14158, 12878, 13390, 13646, 10574, 10062, 10062, 10126, 0xffff };
@@ -8,18 +16,20 @@ const uint16_t notes[] = { 12846, 12334, 11086, 10062, 10062, 9806, 10062, 10574
 
 struct cvu_music music;
 
+// change screen colors to show how long the music
+// routine takes to run after screen interrupt
 void play(void)
 {
-	cv_set_colors(CV_COLOR_BLACK, CV_COLOR_BLUE);
-	cvu_play_music(&music);
-	cv_set_colors(CV_COLOR_BLACK, CV_COLOR_BLACK);
+  cv_set_colors(CV_COLOR_BLACK, CV_COLOR_BLUE);
+  cvu_play_music(&music);
+  cv_set_colors(CV_COLOR_BLACK, CV_COLOR_BLACK);
 }
 
 void main(void)
 {
-	cvu_init_music(&music);
-	music.notes = notes;
-	cv_set_vint_handler(&play);
-	cv_set_screen_active(true);
-	for(;;);
+  cvu_init_music(&music);
+  music.notes = notes;
+  cv_set_vint_handler(&play);
+  cv_set_screen_active(true);
+  for(;;);
 }
diff --git a/presets/coleco/stars.c b/presets/coleco/stars.c
index 23662d40..5afefcf2 100644
--- a/presets/coleco/stars.c
+++ b/presets/coleco/stars.c
@@ -1,11 +1,35 @@
 
+/*
+This is a demo of an animated starfield.
+The TMS9918 has no scrolling registers, so scrolling
+requires rewriting the pattern table on each frame.
+
+There is actually only one star in the pattern table,
+just a single pixel. We move it vertically between 16
+different character tiles (8 * 16 = 128 pixels high).
+We then draw vertical stripes of 8 repeating consecutive
+characters into the image table.
+
+By randomly offsetting where we begin each stripe, we
+create what appears to be a random starfield.
+(If you look closely, you'll see there's exactly two
+stars for every 8-pixel-wide vertical column.)
+
+This demo uses an interrupt handler to increment a
+counter 60 times per second. We use this counter to
+determine the new position of the star pixel when we animate.
+*/
+
 #include <cv.h>
 #include <cvu.h>
 
+//#link "common.c"
 #include "common.h"
 
+// the starting character index in the pattern table
 char starfield_base_char = 240;
 
+// a random offset for every vertical column
 const char star_yoffsets[32] = {
   31, 11, 25, 10, 21, 1, 9, 6,
   22, 3, 7, 14, 15, 18, 0, 29,
@@ -13,39 +37,48 @@ const char star_yoffsets[32] = {
   13, 8, 26, 19, 23, 27, 2, 4
 };
 
+// returns the tile index for every (x,y) position
 byte starfield_get_tile_xy(byte x, byte y) {
   return ((star_yoffsets[x] + y) & 15) + starfield_base_char;
 }
 
+// set up starfield image and pattern table
 void starfield_setup() {
   // clear star patterns
   cvu_vmemset(PATTERN+starfield_base_char*8, 0, 16*8);
+  // write starfield image table
   for (byte x=0; x<32; x++) {
     for (byte y=0; y<28; y++) {
       putcharxy(x, y, starfield_get_tile_xy(x, y));
     }
+    // set value in color table for each character
     cvu_voutb(COLOR_FG(CV_COLOR_WHITE),
               COLOR+((starfield_base_char+x)>>3));
   }
 }
 
+// call each frame to animate starfield
 void starfield_update() {
   static byte oldcounter;
   const byte mask = 0x7f; // 128 star bytes
+  // interrupt counter increments every frame
+  // use this value to determine new star position
   byte counter = vint_counter;
+  // base address in pattern table
   word base = PATTERN + starfield_base_char * 8;
   // erase old star, create new star in pattern table
   cvu_voutb(0, base + (oldcounter & mask));
   cvu_voutb(8, base + (counter & mask));
+  // make sure we remember counter value to erase
+  // in case we skip a frame
   oldcounter = counter;
 }
 
 #ifdef __MAIN__
 
-//#link "common.c"
-
 void main() {
   vdp_setup();
+  // set up default interrupt handler
   cv_set_vint_handler(&vint_handler);
   starfield_setup();
   cv_set_screen_active(true);
diff --git a/presets/coleco/text.c b/presets/coleco/text.c
index 1c24aec4..af631a36 100644
--- a/presets/coleco/text.c
+++ b/presets/coleco/text.c
@@ -1,4 +1,9 @@
 
+/*
+This is a demonstration of the TMS9928A's
+40 x 24 monochrome text mode.
+*/
+
 #include <cv.h>
 #include <cvu.h>
 
@@ -6,22 +11,31 @@
 //#link "common.c"
 
 void setup_text_mode() {
+  // set screen mode to text
   cv_set_screen_mode(CV_SCREENMODE_TEXT);
+  // set image table address, which defines grid of characters
   cv_set_image_table(IMAGE);
+  // set pattern table address, which defines character graphics
   cv_set_character_pattern_t(PATTERN);
+  // clear VRAM to all zeroes
   cvu_vmemset(0, 0, 0x4000);
+  // copy default character set from ROM to VRAM
   copy_default_character_set();
 }
 
 void show_text() {
+  // set background and foreground colors
   cv_set_colors(CV_COLOR_LIGHT_GREEN, CV_COLOR_BLACK);
+  // fill image table with '.' characters
   cvu_vmemset(IMAGE, '.', 40*24);
-  cvu_memtovmemcpy(IMAGE + 1, "Hello Professor Falken", 22);
+  // draw message at row 0, column 1
+  cvu_memtovmemcpy(IMAGE + 1, "Greetings Professor Falken", 26);
+  // turn on display
   cv_set_screen_active(true);
 }
 
 void main() {
   setup_text_mode();
   show_text();
-  while (1);
+  while (1); // infinite loop
 }
diff --git a/presets/coleco/text32.c b/presets/coleco/text32.c
index 85a79cf7..4bf2370c 100644
--- a/presets/coleco/text32.c
+++ b/presets/coleco/text32.c
@@ -1,4 +1,14 @@
 
+/*
+Demonstration of "standard" mode, which is 32 x 24
+characters. Each cell can have its own background and
+foreground color, determined by the character in its
+place. The color table contains 32 bytes, each byte
+controlling the colors of a range of 8 characters.
+For example, the first byte determines colors for
+characters 0-7, the second byte for 8-15, etc.
+*/
+
 #include <cv.h>
 #include <cvu.h>
 
@@ -20,7 +30,7 @@ void setup_32_column_font() {
 
 void show_text() {
   cvu_vmemset(IMAGE, '.', 32*24);
-  cvu_memtovmemcpy(IMAGE + 1, "Hello Professor Falken", 22);
+  cvu_memtovmemcpy(IMAGE + 1, "Greetings Professor Falken", 26);
   cv_set_screen_active(true);
 }
 
@@ -29,6 +39,8 @@ void main() {
   setup_32_column_font();
   show_text();
   while (1) {
-    cvu_vmemset(COLOR+8, i++, 4); // set color for chars 64-95
+    /*
+    cvu_vmemset(COLOR+8, i++, 4); // animate color for chars 64-95
+    */
   }
 }