Lode Runner

01 · Disk and cartridge

Two engines, shared rooms

The supplied CRT is labelled “Official Cartridge Image” and contains a 16 KB cartridge engine. Its room data, graphics, and sound directory differ from the disk program. The How it works and Source tabs cover the Black Label resident disk engine and its 150 room loads; this page collects the checked cartridge comparisons.

Black Label disk playing room one, with 250 points — Black Label disk · room one

Official Cartridge Image playing its first room, with zero points — Official Cartridge Image · room one

Room one is shared by both engines. These native play captures were taken at different moments.

02 · Differences

What changes between editions

Property	Black Label disk	Supplied cartridge
Stored rooms	150 disk sectors	17 resident boards
Room loading	A separate sector read for each board; the engine stays resident	All 17 boards reside with the cartridge engine
Room encoding	Two cells per byte; 224 cell bytes per room	Runs of 1–16 cells; 2,612 bytes total
Source glyphs	104	76, expanded into RAM
Completion motifs	10	7
Timer interrupts per undelayed main-loop pass	2	3
Main-loop passes measured over 120 PAL frames	72	48
Approximate default main-loop pace	30 passes/second	20 passes/second

Both timing captures counted 144 interrupts over those 120 PAL frames. The rates describe the tested PAL setup's undelayed loops; pauses and other work can extend an update.

The cartridge’s default main loop waits for three timer interrupts per pass, while the disk waits for two. This accounts for the slower cartridge pace in the timing captures.

The picture gallery shows each edition’s graphics, using the gameplay sprite masks for actors. Each edition has its own source indexes. The Music tab explains the different motif cycles and their shared pitch-offset range.

03 · Room order

The cartridge’s 17 rooms

Every cartridge board matches exactly one of the disk’s 150 boards. The cartridge’s third board is disk room 111, so the sequence jumps across the disk set. Each number below opens that room in Maps / levels.

Cartridge room	Matching disk room
1	1
2	5
3	111
4	46
5	50
6	11
7	4
8	12
9	100
10	33
11	48
12	84
13	14
14	64
15	6
16	134
17	150

All 17 original cartridge expansions match the disk cell data. The map browser uses disk artwork for both editions.

Cartridge rooms are stored as runs of repeated cells. A descriptor puts the tile ID in its low nibble and the run length minus one in its high nibble. Each board expands to the same 448 cells used on disk.

On disk, the reader skips raw sector byte zero, then loads the 224 packed cell bytes from offsets 1–224. Each byte supplies two cells, with the low nibble read first. $71F5, $6FA6.

04 · Shared mechanics

Rules that agree

Both engines give the same guard route costs for every legal row and column combination. Their score arithmetic also agrees, including overflow and the eighth digit that stays in the counter while the display shows seven. $81CE, $87E6.

Centered tile tests agree for every persistent tile type in five approaches. The runner falls through a trapdoor from above. Sideways and upward entry are blocked.

Those checks cover selected routines. The complete cartridge controls, editor workflow, and persistence behavior remain outside this comparison.

05 · Supplied disks

Black, Gray, and Yellow Label copies

All three supplied disk images contain identical room sectors for the 150 boards. Their engine payloads differ, and the score-sector data also differs.

Supplied image	IT engine bytes differing from Black Label
Black Label	Reference image
Gray Label	10
Yellow Label	275

The Gray changes include startup selection and disk-probe values. Yellow also changes startup and has additional loader/protection files. Both copies boot natively; their attract screens show the same opening boards. The Source tab follows the Black Label engine, with loader internals and external disk protection outside its scope.

06 · Evidence

Where the comparisons come from

The Source tab’s technical reference records the original-code checks and live timing captures. Cartridge addresses belong to a separate program and are recorded there; addresses linked into this site’s Source tab refer to the disk engine.

The supplied cartridge payload matches the one in the separate cartridge disassembly. Reassembling that source reproduced every payload byte. The cartridge comparison here checks selected behavior from that engine; the complete disk listing has its own coverage record.