diff --git a/libsrc/apple2/apple2-280-192-8.s b/libsrc/apple2/apple2-280-192-8.s
index 3b99a242e..e905a8aec 100644
--- a/libsrc/apple2/apple2-280-192-8.s
+++ b/libsrc/apple2/apple2-280-192-8.s
@@ -84,7 +84,7 @@ Y2 := ptr4
pages: .byte 2 ; Number of screens available
.byte 7 ; System font X size
.byte 8 ; System font Y size
- .word $100 ; Aspect ratio
+ .word $00EA ; Aspect ratio (based on 4/3 display)
; Next comes the jump table. With the exception of IRQ, all entries must be
; valid and may point to an RTS for test versions (function not implemented).
diff --git a/libsrc/apple2/apple2-40-48-16.s b/libsrc/apple2/apple2-40-48-16.s
index 9054d8c69..1b975cb37 100644
--- a/libsrc/apple2/apple2-40-48-16.s
+++ b/libsrc/apple2/apple2-40-48-16.s
@@ -54,7 +54,7 @@ Y2 := ptr4
.byte 1 ; Number of screens available
.byte 8 ; System font X size
.byte 8 ; System font Y size
- .word $100 ; Aspect ratio
+ .word $0198 ; Aspect ratio (based on 4/3 display)
; Next comes the jump table. With the exception of IRQ, all entries must be
; valid and may point to an RTS for test versions (function not implemented).
diff --git a/libsrc/atari/atari-10.s b/libsrc/atari/atari-10.s
index 5d86c420e..7a1e451d2 100644
--- a/libsrc/atari/atari-10.s
+++ b/libsrc/atari/atari-10.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0400 ; 4:1
+ aspect = $0330 ; based on 4/3 display
; Free memory needed
mem_needed = 7147
; Number of screen pages
diff --git a/libsrc/atari/atari-10p2.s b/libsrc/atari/atari-10p2.s
index 35581cf12..228739d76 100644
--- a/libsrc/atari/atari-10p2.s
+++ b/libsrc/atari/atari-10p2.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0400 ; 4:1
+ aspect = $0330 ; based on 4/3 display
; Free memory needed
mem_needed = 15339
; Number of screen pages
diff --git a/libsrc/atari/atari-11.s b/libsrc/atari/atari-11.s
index 5d3c163e5..51bae0a4f 100644
--- a/libsrc/atari/atari-11.s
+++ b/libsrc/atari/atari-11.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0400 ; 4:1
+ aspect = $0330 ; based on 4/3 display
; Free memory needed
mem_needed = 7147
; Number of screen pages
diff --git a/libsrc/atari/atari-14.s b/libsrc/atari/atari-14.s
index 70092ad2f..9fd10e913 100644
--- a/libsrc/atari/atari-14.s
+++ b/libsrc/atari/atari-14.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0200 ; 2:1
+ aspect = $0198 ; based on 4/3 display
; Free memory needed
mem_needed = 3305
; Number of screen pages
diff --git a/libsrc/atari/atari-15.s b/libsrc/atari/atari-15.s
index 70f535e57..be37c72ad 100644
--- a/libsrc/atari/atari-15.s
+++ b/libsrc/atari/atari-15.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0200 ; 2:1
+ aspect = $0198 ; based on 4/3 display
; Free memory needed
mem_needed = 7147
; Number of screen pages
diff --git a/libsrc/atari/atari-15p2.s b/libsrc/atari/atari-15p2.s
index b02574700..a49558dbd 100644
--- a/libsrc/atari/atari-15p2.s
+++ b/libsrc/atari/atari-15p2.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0200 ; 2:1
+ aspect = $0198 ; based on 4/3 display
; Free memory needed
mem_needed = 15339
; Number of screen pages
diff --git a/libsrc/atari/atari-3.s b/libsrc/atari/atari-3.s
index 7663b6fdf..9034a9c7f 100644
--- a/libsrc/atari/atari-3.s
+++ b/libsrc/atari/atari-3.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0100 ; 1:1
+ aspect = $00CC ; based on 4/3 display
; Free memory needed
mem_needed = 1
; Number of screen pages
diff --git a/libsrc/atari/atari-4.s b/libsrc/atari/atari-4.s
index 81383fa7b..360f2d049 100644
--- a/libsrc/atari/atari-4.s
+++ b/libsrc/atari/atari-4.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0100 ; 1:1
+ aspect = $00CC ; based on 4/3 display
; Free memory needed
mem_needed = 1
; Number of screen pages
diff --git a/libsrc/atari/atari-5.s b/libsrc/atari/atari-5.s
index c8b1db1db..bd4e3dacd 100644
--- a/libsrc/atari/atari-5.s
+++ b/libsrc/atari/atari-5.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0100 ; 1:1
+ aspect = $00CC ; based on 4/3 display
; Free memory needed
mem_needed = 185
; Number of screen pages
diff --git a/libsrc/atari/atari-6.s b/libsrc/atari/atari-6.s
index d9190720c..58b1f4686 100644
--- a/libsrc/atari/atari-6.s
+++ b/libsrc/atari/atari-6.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0100 ; 1:1
+ aspect = $00CC ; based on 4/3 display
; Free memory needed
mem_needed = 1193
; Number of screen pages
diff --git a/libsrc/atari/atari-7.s b/libsrc/atari/atari-7.s
index 5b86509d3..a09d149b9 100644
--- a/libsrc/atari/atari-7.s
+++ b/libsrc/atari/atari-7.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0100 ; 1:1
+ aspect = $00CC ; based on 4/3 display
; Free memory needed
mem_needed = 3209
; Number of screen pages
diff --git a/libsrc/atari/atari-8.s b/libsrc/atari/atari-8.s
index c7852d843..b609114d5 100644
--- a/libsrc/atari/atari-8.s
+++ b/libsrc/atari/atari-8.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0100 ; 1:1
+ aspect = $00CC ; based on 4/3 display
; Free memory needed
mem_needed = 7147
; Number of screen pages
diff --git a/libsrc/atari/atari-8p2.s b/libsrc/atari/atari-8p2.s
index b9fc62638..314da1b9d 100644
--- a/libsrc/atari/atari-8p2.s
+++ b/libsrc/atari/atari-8p2.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0100 ; 1:1
+ aspect = $00CC ; based on 4/3 display
; Free memory needed
mem_needed = 15339
; Number of screen pages
diff --git a/libsrc/atari/atari-9.s b/libsrc/atari/atari-9.s
index e5f064760..4cd43bb1a 100644
--- a/libsrc/atari/atari-9.s
+++ b/libsrc/atari/atari-9.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0400 ; 4:1
+ aspect = $0330 ; based on 4/3 display
; Free memory needed
mem_needed = 7147
; Number of screen pages
diff --git a/libsrc/atari/atari-9p2.s b/libsrc/atari/atari-9p2.s
index 6789a60f1..4f6dcec67 100644
--- a/libsrc/atari/atari-9p2.s
+++ b/libsrc/atari/atari-9p2.s
@@ -34,7 +34,7 @@
; Screen memory size in bytes
scrsize = x_res * y_res / ppb
; Pixel aspect ratio
- aspect = $0400 ; 4:1
+ aspect = $0330 ; based on 4/3 display
; Free memory needed
mem_needed = 15339
; Number of screen pages
diff --git a/libsrc/atmos/atmos-240-200-2.s b/libsrc/atmos/atmos-240-200-2.s
index 72887db4a..f978f36b9 100644
--- a/libsrc/atmos/atmos-240-200-2.s
+++ b/libsrc/atmos/atmos-240-200-2.s
@@ -29,7 +29,7 @@
.byte 1 ; Number of screens available
xsize: .byte 6 ; System font X size
.byte 8 ; System font Y size
- .word $100 ; Aspect ratio
+ .word $011C ; Aspect ratio (based on 4/3 display)
; Next comes the jump table. Currently all entries must be valid and may point
; to an RTS for test versions (function not implemented).
diff --git a/libsrc/c128/c128-640-200-2.s b/libsrc/c128/c128-640-200-2.s
index 6f8118932..9055e0dc3 100644
--- a/libsrc/c128/c128-640-200-2.s
+++ b/libsrc/c128/c128-640-200-2.s
@@ -62,7 +62,7 @@ yres: .word 200 ; Y resolution
pages: .byte 1 ; Number of screens available
.byte 8 ; System font X size
.byte 8 ; System font Y size
- .word $100 ; Aspect ratio
+ .word $006A ; Aspect ratio (based on 4/3 display)
; Next comes the jump table. Currently all entries must be valid and may point
; to an RTS for test versions (function not implemented).
diff --git a/libsrc/c128/c128-640-480-2.s b/libsrc/c128/c128-640-480-2.s
index 0f03e7096..43599dec4 100644
--- a/libsrc/c128/c128-640-480-2.s
+++ b/libsrc/c128/c128-640-480-2.s
@@ -63,7 +63,7 @@ yres: .word 480 ; Y resolution
pages: .byte 0 ; Number of screens available
.byte 8 ; System font X size
.byte 8 ; System font Y size
- .word $100 ; Aspect ratio
+ .word $0100 ; Aspect ratio (based on 4/3 display)
; Next comes the jump table. Currently all entries must be valid and may point
; to an RTS for test versions (function not implemented).
diff --git a/libsrc/c64/c64-320-200-2.s b/libsrc/c64/c64-320-200-2.s
index e711dc6b8..65b0076a9 100644
--- a/libsrc/c64/c64-320-200-2.s
+++ b/libsrc/c64/c64-320-200-2.s
@@ -30,7 +30,7 @@
.byte 1 ; Number of screens available
.byte 8 ; System font X size
.byte 8 ; System font Y size
- .word $100 ; Aspect ratio
+ .word $00D4 ; Aspect ratio (based on 4/3 display)
; Next comes the jump table. With the exception of IRQ, all entries must be
; valid and may point to an RTS for test versions (function not implemented).