Yes, the NES/Famicom is a interesting and weird piece of hardware. Not only that it is a old device with limited capabilities, it also has some strange hardware registrations, several types of MMCs (Memory Management Chips), a big bunch of different cartridge mappers (responsible for how to read the ROM data?), different lookout chips with country codes and so on. But keep on reading. The informations to follow will be much more detailed and proffessional.
 

Hardware:

As in all other computers, the Nintendo is controlled by software. The software is on the cartridge which you put into your NES just like a computer disk. When you put your cartridge into your NES, the end of the cartridge which has an opening i put into a slot. The console and the cartridge now has "contact". The informations can now go from the cartridge chip to the Central Processing Unit (CPU) or the Picture Processing Unit (PPU) in the console.
If there is dust between the console and the cartridge, the game might not work, so remember: KEEP YOUR CARTRIDGES CLEAN!!!
Did you know, that your NES is like a TV-transmitter? It transmits waves which you TV can receive. The PPU is sending a compositive videosignal, but many TV's cannot receive this signal, so it has to be converted to a RF-signal in the RF-modulator. The RF-signal which the RF-modulator makes, is changed to a compositive signal when it's inside the TV. This means, that you might loose some picture quality, but if you have a TV with SCART/EUROPEAN - connection, you can buy a cable which does that you can use compositive signals.
The console also gets informations from the joypad. When the CPU needs informations from the joypad, it sends a message to the a memory in the joypad. The memory tells the CPU when the buttons are pressed. This might sound like it takes quite awhile before the CPU knows what to do, but it happends in less than half a second.
The PPU (Picture Prosessing Unit) is just like the CPU placed on the motherboard. The PPU gets digital informations ( 0' and 1') from the CPU and the cartridges and converts then to composive signals which controlls every pixel and colour on the screen. 50 times per second, the PPU gets this information and draws the screen again. Because it goes this fast, it's like the figures moves.
The CPU (Central Prosessing Unit) is a kind of a little telephonecentral with a huge capacity. It makes thousands of "phonecalls" in and out all the time. Every 50th second when a new screen is drawn, the CPU checks if there are any interupts. These commands comes from the cartridge which tells the CPU to ask the Joypad about a position, or that the CPU has to send a sound signal to the TV's speaker. Imagine, that the cartridge is a cookbook and the CPU is the cook, who follows the instructions in the book there is just one difference... the CPU make it all at the same time.
 

NES/Famicom Specs:
Processor:	custom Motorola NMOS 6502 @ 1.7897725 Mhz
Resolution:	256 x 240 pixel
Colors:	16 out of 52
Sprites:	max. 64, max. 8 per line
Sprite size:	8 x 8 or 8 x 16
Picture Scroll:	2 h.v
RAM:	2KByte others say: 8KByte with MMC to get over 16bit (64 KByte programm counter boundaries)
Video RAM:	2KByte
Sound:	5 channels

Software:

NES Software consists of a PRG-ROM (Program ROM) which is the code area and a CHR-RAM (Character RAM) which is the pattern table.
Most games load themselves into the Lower PRG-ROM ($8000), using 32kb of PRG-ROM space. The first game to use the entire PRG-ROM space is Super Mario Brothers. However, all games with more than one (1) 16K bank of PRG-ROM load themselves into $8000 as well. These games use MMCs (see section 2.5) to address PRG-ROM past the 32K boundary, and to access more than 8K of CHR-RAM simultaneously.

UNROM Games:

Unrom games come with a built-in PRG ROM chip as well as a RAM chip for memory storage. Such things as background and moving object characters for the current area are stored in the RAM chip until needed. The Unrom also was the first chip to expand the memory size of the NES games and were the first to carry a feature known as bank switching for the games.
This effect allowed for many pages of information and to have serveral programs on one chip. Back switching allowed for automatic switching between multiple programs on one chip. Also, the maximum game page size was 8x16kb, just like the MMC1 chip.

Memory Management Chips:

MMC1	The first and most used chip of all five. Many games like the Legend of Zelda and Metroid use this chip because otherwise they would not be possible. The MMC1 allows NES games to have the ability to scroll vertically and horizontally at the same time on the screen. The chip also expanded the NES memory to allow for more, and larger game worlds. The maximum game page size is 8x16kb.
MMC2	This chip is only found in the US and European Mike Tyson's Punch-Out, the Japanese version used a MMC4 chip. It was entirely used for the purpose af allowing large characters to move on the screen. The chip also allowed for you to see expression on an opponents face. This could be a dropped jaw, blinking, shock, a wince, twitching, as well as hand and feet movements. The game, because of all its different variations, required a big memory boost which this chip allowed for. The maximum game page size of this chip is 32x16kb. But why were they able to use a MMC4 for the Japanese version then? I don't know.
MMC3	Second most used chip for NES carts allowed for many new game innovations. The additions are: expanded memory and the use of split screen scrolling in games. Games like Super Mario Bros 3 use this chip. In SMB3 it's used as a split screen between the playing field and the status screen at the bottom of the screen. These games also has a maximum game page size of 32x16kb, just as the MMC2.
MMC4	? (see MMC2)
MMC5	The newest of the MMC chips for the NES. The first game it was used for was Castlevania 3: Draculas Curse. This chip has many new and expanded features that accompanied it. The MMC5 improved the battery backup feature so you wouldn't have to push reset when you turn off the NES to prevent data loss. The chip also allows greater color definition and partial screen scrolling (not locked like SMB3). It is also a customized mathematics module that took much strain off the CPU and took care of many tasks like the internal clock, and other repetitive functions. The MMC5 also allowed a vertical split screen scroll which means you can have a side bar of information while the scrolling action of the game continues. The chip has a memory capacity of 8 Megs (1,048,576 bits). Another MMC5 game, and probably the only one, is Kirby's Adventure. A few games which this chip had a maximum game page size of 64x16kb.

 

Lockout Chip:

Nintendo used at least 3 different types. There were different types used for the USA, UK, and Europe. Europeans have always been told by Nintendo that games could not be bought all over Europe an then work in their NES.
Europe was divided up in the following parts:

Scandinavia	=	Finland, Sweden, Norway, Island and Denmark.
?	=	Germany and Austria.
?	=	Belgium, Holland and France.
United Kingdom	=	England, Scotland, ??.
?	=	Spain

More to come soon....

Anyway, what Nintendo said is untrue because on my trips to other countries in Europe I took to chance and bought games which Nintendo claimed did not work in my Scandinavian NES unit, they did without any complications though.
Only games from United Kingdom will not work in the other European NES units and vice versa, because the UK uses another PAL standard than the rest of Europe. The PAL games were marked "B" or "REV-A". REV-A was the UK games and the "B" labeled carts were used in the rest of Europe.

Game Pak codes are (xx is the games ID which is different from game to game):
 

NES-xx-UKV	=	United Kingdom
NES-xx-FRA	=	France???
NES-xx-SCN	=	Scandinavia (Finland, Denmark, Sweden, Norway, Island).
NES-xx-FRG	=	Germany.
NES-xx-NOE	=	"Nintendo of Europe" (Germany).
NES-xx-USA	=	United States.
NES-xx-EEC	=	? (Scandinavia)
NES-xx-ESP	=	Spain

 

Nintendo removed the lockout chip from the redesigned top-loading NES.

Some unlicensed games contain circuitry which *requires* that a security chip be present. For example, the game Firehawk by Codemasters works on both a UK NES and an old-style US NES. It fails to work on my new-style US NES and the European NES. Another Codemasters game, Quattro Adventure, works on an UK NES but fails to work on either of the US NES models an the European NES.