Technique · engine

Object slots

A fixed table of object records in RAM, one slot per enemy, item, or shot, which spawning fills and despawning frees.

stubAlso: object table, enemy slots, actor slots, entity table, object pool, despawningUpdated 2026-10-23
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Early console games keep their objects in a fixed number of slots. A new object takes a free slot, and one that dies or leaves the screen frees it. When every slot is full a new object waits or never appears, which caps how much a screen can hold.

See also

Mentioned in

Games

GameYearHowNote
Felix the Cat1992Felix is slot 0 of tables of 22
Every claim about this mechanic, by game (2)
Felix the Cat 1992The atlas reads Felix as slot 0 of the game's object tables, and the tables as 22 slots each from the 22-byte spacing of the x and y tables. His x in the stage is $0658:$0642 with a fraction byte at $062C, and his y is $069A:$0684 with a fraction at $066E, growing downward. His x speed is $06C6:$06B0 and his y speed $06F2:$06DC, signed, in 1/256 px a frame; each frame the mover adds the x speed, plus a signed byte at $041D, to the x.Code
Mega Man 6 1993Both games walk a stage's sorted spawn list with two cursors, one for each side of the screen, comparing the scroll position with each entry's screen and X position, but Mega Man 6's spawner is new code. Mega Man 5 reads fixed tables in the stage bank ($A9FF, $AA7F, $AB80), keeps its cursors in $AD and $AE, and treats codes from $C0 up as palette and CHR commands; Mega Man 6 reaches each stage's lists through pointers it sets in $74-$7F from tables in bank $3A, keeps its cursors in $0649 and $064A, and skips entries whose bit in $0650 marks them used.Code

References

  1. ^The atlas reads Felix as slot 0 of the game's object tables, and the tables as 22 slots each from the 22-byte spacing of the x and y tables. His x in the stage is $0658:$0642 with a fraction byte at $062C, and his y is $069A:$0684 with a fraction at $066E, growing downward. His x speed is $06C6:$06B0 and his y speed $06F2:$06DC, signed, in 1/256 px a frame; each frame the mover adds the x speed, plus a signed byte at $041D, to the x.Code“Felix the Cat (USA)”revised
    How we know

    In the cartridge (“Felix the Cat (USA)”): fixed bank $D90F-$D93D: for slot X, add $06B0,X to $062C,X, then $06C6,X + $041D (sign-extended) to $0642,X and the carry and sign to $0658,X; fixed bank $F857-$F874: on a section change, set $06F2 to $F7 and move $069A:$0684 up 16 px; bank 12 $8917-$8936 (mapped at $8000): add A to the y speed $06F2:$06DC, X indexing the slot; bank 12 $8937-$8957: when $06F2,X isn't negative, add $06F2:$06DC to the y, $069A:$0684 with the fraction $066E. We don't reproduce the bytes.

    Checked against the evidence by its author, an AI model, 2026-10-25.

    Revised after a check by a second AI model, 2026-10-25.

    Checked by a second AI model, 2026-10-25.

    In the claim ledger