Apple II Video Memory
Apple II HGR GBAS Calculator
Section 0 | Group 0 | Line 0
Binary Breakdown
00000000
ABC = Section |
DEF = Group |
GH = Line
ABC (Section)
000 = 0
× $28 in high byte
DEF (Group)
000 = 0
× $04 in high byte
GH (Line)
00 = 0
$00 in low byte
Calculation Steps
Base HGR Address:
$2000
High Byte = $20 + (DEF × $04) + (ABC × $28):
$20 + (0 × $04) + (0 × $28) = $20
Low Byte (GH determines $00 or $80):
$00
Final Address:
$2000
Memory Layout Visualization
Each cell shows a Y coordinate and its memory address
Section 0 (Y 0-63)
Section 1 (Y 64-127)
Section 2 (Y 128-191)
Note: The Apple II HGR screen uses a complex interleaved memory layout for performance reasons.
Lines are grouped into three 64-line sections, then into groups of 8 lines within each section.
This arrangement minimized memory refresh overhead on the original hardware.