"Mapper" is iNES's term for a set of NES cartridge boards that behave in a similar fashion. The NES's 6502-compatible 2A03 CPU has only 16 address lines and 8 data lines, and addresses $0000-$4017 are mapped to NES internal hardware. The NES PPU has 14 address lines and 8 data lines to the cart edge. Mapper hardware is present in most cartridges to provide more address lines under software control so as to allow more than 32 KB of ROM to be accessed. Similar concepts are present in the sideways ROM mods for BBC microcomputers.

How a mapper works

I'll use UNROM as the example. Other mappers are more complex but operate on similar principles.
2A03 address bus     A15432 1098 7654 3210
                       |||| |||| |||| ||||
 ,---------------------'||| |||| |||| ||||
 | D3-D0-.      ,-------'|| |||| |||| ||||
 |       |    . |        || |||| |||| ||||
 | ,-----+--. |`+.       || |||| |||| ||||
 | |Register+-+0  `.     || |||| |||| ||||
 | `--------' |    |___  || |||| |||| ||||
 |       |    |    | ||| || |||| |||| ||||
 | R/W --'  7-+1  ,' ||| || |||| |||| ||||
 |            | ,'   ||| || |||| |||| ||||
 |            |'     ||| || |||| |||| ||||
 |                   ||| || |||| |||| ||||
,+-------------------+++-++-++++-++++-++++-.
|EN                A1654 32 1098 7654 3210 |
|         128 kilo by 8 bit ROM       D7-D0+-- to 2A03 data bus
|                                          |
`------------------------------------------'
Writes to the program area $8000-$FFFF will load a new value into the register and subsequently to the most significant bits of the ROM's address bus, mapping a 16 KB bank into $8000-$BFFF. The multiplex with 7 is actually implemented as an OR gate and serves to make sure that the game engine is always available in $C000-$FFFF and that reset and interrupt vectors are always available in $FFFA-$FFFF.

iNES mapper metanode

Mapper 0 refers to a 16 KB or 32 KB program ROM and an 8 KB graphics ROM connected directly to the cartridge edge. This scheme is used on NROM games.
  1. MMC1 (Dr. Mario, Legend of Zelda, Metroid)
  2. UNROM (Contra, Castlevania, Ikari)
  3. CNROM (Gradius, Solar Wars, Panesian titles)
  4. MMC3 (Super Mario Brothers 3, Mega Man 3, Crystalis)
  5. (MMC5) (Castlevania 3, Uncharted Waters, some Koei titles)
  6. (FFE F4K) (Front Far East copier; similar to Konami VRCs)
  7. AOROM (Rare titles such as Battletoads)
  8. (FFE F3K) (more Front Far East copier games)
  9. MMC2 (Punch-Out!! with and without Mike Tyson)
  10. MMC4 (enhanced MMC2 in Family War and Fire Emblem)
  11. (Color Dreams mapper) (Crystal Mines/Exodus (the boulderdash clone not the ultima game), Pesterminator, King of Kings, Menace Beach/Sunday Funday)
  12. 12 is unknown.
  13. 13 is unknown.
  14. 14 is unknown.
  15. (100-in-1 Contra Function 16)
  16. (Bandai mapper) (Gundam Wing, Dragonball Z)
  17. (FFE F8K) (more Front Far East games)
  18. (Jaleco SS8806) (Japanese Jaleco titles such as Baseball 3)
  19. (Namcot 106) (Japanese Namcot titles such as Splatterhouse and Family Stadium '90)
  20. 20 is unknown.
  21. (Konami VRC4) (Wai Wai World 2, Gradius 2)
  22. (Konami VRC2 type A) (Twinbee 3)
  23. (Konami VRC2 type B) (Japanese Contra, Getsufuu Maden)
  24. (Konami VRC6) (Japanese Castlevania 3)
  25. ???
  26. ???
  27. ???
  28. ???
  29. ???
  30. ???
  31. ???
  32. (Irem G-101) (ImageFight 2)
  33. (Taito TC0190) (Japanese Taito titles such as Pon Poko Pon)
  34. (Nina-1) boards (Deadly Towers, Impossible Mission II)
  35. nothing
  36. nothing
  37. nothing
  38. (Tengen RAMBO-1) (similar to MMC3; used on Klax and Shinobi)
  39. (Irem H-3001) (Japanese Irem titles such as Daiku no Gensan 2)
  40. (GNROM) (Gumshoe, Dragon Power, original Dragonball)
  41. (Sunsoft Mapper 4) (Afterburner II)
  42. (Sunsoft FME-7) (Batman: Return of the Joker, several Japanese titles)
  43. Codemasters mapper (nearly identical to UNROM)
  44. Irem 74HC161/32 (similar to FFE F3K)
  45. (HK-SF3) (pirate Street Fighter III)

Most popular cartridges in the US use MMC1, UNROM, or MMC3; emulating these accurately will run most games.

Source: Firebug's mapper document version 0.80

(return to) NES programming metanode

The Ways of Mappers and Packers

It is a surprise to discover that there are two distinct states of mind around us. It is similar to the experience of learning that someone you've known for months is illiterate. At first you are astonished: this cannot be possible! But then you realise how someone else can live a life very different to yours, that looks superficially almost the same.

In this section we look at traits of the two strategies. As we do so, many of the woes of the modern age, particularly in high tech disciplines, will come into a simple picture - the mark of a useful theory! Remember, most people, be they mappers or packers, have no reason to believe there is any other state of mind but theirs.

What is packing? Well, you just stop yourself asking `Why?'. You never really clean up your map of the world, so you don't find many of the underlying patterns that mappers use to `cheat'. You learn slower, because you learn little pockets of knowledge that you can't check all the way through, so lots of little problems crop up. You rarely get to the point where you've got so much of the map sorted out you can just see how the rest of it develops. In thinking-intensive areas like maths and physics, mappers can understand enough to get good GCSE grades in two weeks, while most schools have to spend three years or more bashing the knowledge packets into rote-learned memory, where they sit unexamined because the kids are good and do not daydream. It really isn't a very efficient way to go about things in the Information Age.

With no map of the world that checks out against itself and explains just about everything you can see, it is very hard to be confident about what to do. The approach you have to take in any situation is to cast about frantically until you find a little packet of knowledge that kind of fits (everything has a little bit of daydreaming at its core, but the confused objective is to stop it as soon as humanly possible). Then you list the bits that kind of fit, and you assert that the situation is one of those, so the response is specified by your `knowledge'.

Your friend has happened to grab another packet of `knowledge' and so you begin an `argument' where your friend lists bits of your knowledge that don't fit and says that you are wrong and he is right, and you do the same thing. You don't attempt to build a map that includes both your bits of knowledge and so illuminates the true answer because you don't have access to the necessary faculty of mapping, and anyway, without the experience, it is hard to believe that it is possible in the time allowed. Being devoid of the clarity that comes from a half-way decent map, you would rather do something ineffective by the deadline than something that might even work. Then when things go pear-shaped you say it is bad luck.

The consequences go further. Not having a big map means that you often don't understand what is happening, even in familiar settings like your home or workplace. You assume that this means that you do not possess the appropriate knowledge packet, and this may be seen as a moral failure on your part. After all, you have been told since childhood that the good acquire knowledge packets and stack them up in their heads like dinner plates, the lazy do not.

You are also overly concerned about certainty. Mappers have a rich, strong, self-connected structure they can explore in detail and check the situation and their actions against. Logic for them is being true to the map, and being honest when it stops working. It's not a problem, they just change it until it's `logical' again. Without mapping, you have to use rickety chains of reasoning that are really only supported at one end. Because they are rickety you get very worried that each link is absolute, certain, totally correct (which you can never actually achieve). You have to discount evidence that is not `certain' (although tragically it might be if your map was bigger), and often constrain your actions to those that you can convince yourself are totally certain in an inherently uncertain world.

The issue of certainty then becomes dominant. People are unwilling to think about something (erect a rickety chain) unless they are `certain' that the `procedure' will have a guaranteed payoff, because that, they believe, is how the wise proceed.

You become absorbed by the fear of being found to be `in the wrong', because of the idea that the `good' will have acquired the correct knowledge packet for dealing with any situation. The notion that the world is a closed, fully understood (but not by you) thing kind of creeps in by implication there. The idea of a new situation becomes so unlikely that you rarely spot one when it happens, although mappers notice new situations all the time. Your approach becomes focussed on actions that you cannot be `blamed' for, even though their futility or even counter-productivity is obvious. You insist on your specific actions being specified in your job, even when your map is already easily good enough for you to accept personal responsibility for the objectives that need to be achieved, which would be more in keeping with your true dignity.

Some people have so little experience of direct understanding, produced by mapping over time, that they cannot believe that anything can be achieved unless someone else spells out in exact detail how to do absolutely everything. They believe that the only alternative to total regimentation is total anarchy, not a bunch of people getting things done.

Now, if you are used to talking to your imaginary friend about your map of the world, and keep finding holes and fixing them, you don't become very attached to the current state of it at any particular time. You do sometimes, if you find an abstraction that was a wonderful surprise when you got it and has been useful, but now needs to go. It's always important to remember that the fun only adds up: if finding something was fun, finding something deeper is even more fun. Generally though, you don't mind your imaginary friend knocking bits off the map if they don't work. So you don't mind real friends doing it either! When you see thing in different ways you try to understand each others' maps and work through the differences. Two messy maps often point the way to a deeper way of seeing things.

Great thinkers are mappers. They rarely proceed by erecting edifices of great conceptual complexity. Rather they show us how to see the world in a simpler way.

Mappers experience learning as an internal process in response to external and self-generated stimuli. Packers experience learning as another task to be performed, usually in a classroom, using appropriate equipment. Particularly in the early years, efficient mapper learning requires internal techniques for exploring conceptual relationships and recognising truths, while efficient packer learning focuses on memorisation skills.

Aspects of mapper learning require higher investment than packer learning, and this has consequences. An emphasis on succinct, structured knowledge means that low structured off-topic considerations can displace disproportionally larger issues from a problem the mapper is contemplating. If a child is trying to understand a new idea in terms of as much as possible of what is already known, then likely the child's awareness will be spread over as much `core knowledge' as possible already. The requirement to then consider the question `Shall I take my library books back today?', bringing with it conceptually networked questions such as `Where is my satchel?', `Will it rain?', `Will it rain tomorrow?' and so on is an imposition on the mind that a packer child would simply not experience in apparently similar circumstances. The packer child simply never has (for example) the form of the flows resulting from economic supply and demand curves (which might also actually be the same representations that are used to hold, say, parts of thermodynamic understanding) floating about to be displaced by a simple question about a library book.

Accepting a fact and being ready for the next is also a different process in mapping and packing. The mapper mind must explore the fact and compare it against core knowledge to see if it is a consequence that already has a place in the mapper's conceptual model of the world, or if it is in fact new fundamental knowledge that requires structural change.

Mappers are likely to be much more aware of the comparative reliability of information. Whereas packers tend to regard knowledge as planar, a series of statements that are the case, mappers tend to cross-index statements to verify and collapse them into more profound truths. Mappers are more likely to work with contingent thinking of the form: `If X is true then Y must be true also, Z is certainly true, and W is nonsense although everyone keeps saying it is the case'. Mappers are likely to be concerned about the soundness of packer reasoning.

An aspect of packer thinking that drives mappers up the wall, is that packers often seem to neither seek out the flaws in their own logic, nor even hear them when they utter them. Worse, when flaws are pointed out to them, they are likely to react by justifying following logic that they cheerfully admit is flawed, on grounds of administrative convenience. The evidence of their own senses is not as important as behaviour learned through repetition, and they seem to have no sense of proportion when performing cost/benefit analyses. This is because packers do not create integrated conceptual pictures from as much as possible of what they know. The mapper may point out a fact, but it is one fact amongst so many. The packer does not have a conceptual picture of the situation that indicates the important issues, so the principal source of guidance is a set of procedural responses that specify action to be taken. The procedure that is selected to be followed will be something of a lottery. For the mapper, one fact that should fit the map but doesn't, means the whole map is suspect. The error could wander around like a lump in a carpet, and end up somewhere really important. Both parties agree that they should do the `logical' thing, but two people can disagree about logic when one sees relationships that the other has only ever been dissuaded from seeing.

Mappers have lots of good ideas based in profound insights into relationships that packers rarely have the opportunity to recognise.

Part of mappers' extraordinary flexibility and learning speed comes from the benefits of seeking understanding rather than data, but some of it comes from the sheer amount of playing with a topic they do. It is quite usual for mappers to spend every spare moment for a week wandering around a topic in their heads, and then spend all weekend focused on it. Mapper focus is a terrible thing. A few hours of it can produce breathtaking results where a team of packers could strive for months. Every IT manager who has ever had an effective mapper around knows this.

Mappers have a linguistic tendency to want to talk in terms of the form of the concentrated knowledge they reduce experience into. Although mappers often use different internal representations of a sphere of discourse, they are adept at negotiating mutually agreed terminology at the onset of discussions between themselves, and this is one way that mappers are able to recognise one another. Mutual recognition occurs because of this series of transactions where one party traces a route through the map, stops, and invites the other to pick up where they left off. The objective of the exercise is to align mental maps, but it also reveals the presence of the other's map in the first place!

Mappers advocate changing descriptions and approaches often, because they see simplification benefits that are of high value to understanding, and whose map is it anyway? In social or administrative situations, this can cause confusion because the mapper does not realise that the packers do not have a map that they can move around in chunks. Mappers see packers as wilfully ignorant, packers see mappers as confused. In software engineering contexts, this failure of communication leads to arguments about `churn'. The mapper wants to move from a large mass of software to a smaller one that is more robust because of its necessary and sufficient structure. The packers are not practiced at seeing the proposed new structure, and see only a maniac who wants to change every single file in one go.

Mappers have a direct, hands-on awareness of the effectiveness of their reflections and so, in most areas, they have a sense of the universe in some unseen way `playing fair' with them, even rewarding them with wonderful surprises when they look deeply enough. This often gives rise to a `spiritual' or `mystical' element to their character, and often to unusually high spirits, even in situations where packers are despondent.

Mappers ensure that the known elements of a problem are held in their minds, before embarking on it. They draw on their own strength of character to find the motivation to do the hard work involved in keeping their background explorations going. To achieve a solution to a problem, a mapper engages all his or her strengths, and is rewarded with elation or a sensation of betrayal if things do not work out well. Mappers are `passionate' about `dry' subjects.

Mappers excel at conceptually challenging work such as complex problem-solving with many inter-related elements. They can perform tasks requiring insight, or imagination, that packers simply cannot do at all. Best quality software engineering, mathematics and physics, with genetics emerging as a likely area of unique contribution, are amongst mapper challenging science disciplines. Amongst the traditionally recognised arts, poetry and music are areas where the mapper faculty for manipulating structure is of particular benefit, although there may be value in redefining the `Arts' as what mappers do well. The very power of great art is only available to mapper thinking, because the artist uses a tone of sound or light, itself representative of nothing, but triggering the recognition of a deep structure. Pointing out the structure can then bring to mind instances of that structure, and the artist has added to the audiences maps!

All these differences are simply consequences of one person having a big map built by a great deal of disciplined daydreaming, and the other not. That these profound differences between two clearly distinct groups of people exist is the major surprise of the approach proposed. It means that it is very unlikely that either kind is likely to have any appreciation of the other's state of mind.

Packing as a Self-Sustaining Condition

We live in an action oriented society. It's been that way since we invented agriculture and developed a stable environment in which the tasks to be performed could be defined within. Not much thinking was needed. We have little experience of discussing and managing subjective, internal states - although they are as much shared experiences as external objects visible to all. We have a general heuristic that says we should confine our observations to the externally visible, which kicks in to prevent the exploration of subjective phenomena even before they have had the chance to give results and justify themselves.

When things go wrong, we seek to clarify action, and capture better descriptions of more effective actions. In situations where flexibility is an asset, this leads to reduced aspirations. If things are proceeding according to the actions written on paper, they are deemed to be going well, and the opportunity cost is not considered.

Worse, the behaviour of people trapped in lack of understanding can reinforce each other. If one person just doesn't understand what is happening, they look about them and see others apparently knowing what they are doing, feel vulnerable, because lack of knowledge packets is supposed to be a personal failure, and therefore they bluster. They stick their noses in the air and waffle about `due consideration' and `appropriate action' as if `undue consideration' or `inappropriate action' was also on the table, but don't suggest what the appropriate action might be.

The thing is, everybody is doing it! So the silent conspiracy to maintain the etiquette of bluster develops. If anyone violates the etiquette, that person will be assailed by inherently unclear objections and other pressures to `conform', apparently for the sake of it. These cannot be countered in action-oriented terms, only by reference to causal relationships that only one person is fully cognizant of. Mapping in a packing world can be a painful and depressing experience, particularly if one does not understand the shattered reality one's packing associates inhabit.

In pathological situations, this can lead to an infinite regress wherein every problem is addressed by attempting to delegate it to someone else, a procedure, or a blame allocation mechanism. It's rather like holding your toothbrush with chopsticks - if you are holding the chopsticks just like on the diagram, the brush up your nose and the paste all over the mirror are not your responsibility!

The Mapper/Packer Communication Barrier

It's worth reiterating some key points here:

  • Mapping and packing are very different strategies
  • Packing is the strongly enforced social norm
  • The world is set up for packers
  • Business language is packer language
  • The results of mapping are called `common sense'
  • Common sense isn't so common
  • Mappers think packers are cynical or lazy
  • Packers think mappers are irrational
  • Packers spend much of their time playing politics
  • The last thing that counts in politics is reason
  • Mappers are often wrong about packer psychology
  • Packers are usually right about packer psychology
  • Mappers are often wrong about mapper psychology
  • Packers are always wrong about mapper psychology.
  • Mappers do not have a culture to guide them
  • Most mappers teach themselves, like Mowgli
  • Mappers can teach themselves!
  • Mappers can learn from others
  • Mappers often face significant social challenges
  • Mappers currently rarely fulfill their potential
  • Once a situation is understood, it can be addressed.
http://www.reciprocality.org/Reciprocality/r0/Day1.html, see also Jock Engineer

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