some cartridge question

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777gamer
Posts: 15
Joined: 19 Nov 2015 03:05

some cartridge question

Post by 777gamer » 29 Feb 2016 02:37

i always see people talk about headers mappers banks checksums and more but i dont know what they are
if someone could explain this i will thank later

KingMike
Posts: 404
Joined: 22 Sep 2012 16:36

Re: some cartridge question

Post by KingMike » 29 Feb 2016 17:00

Headers: blocks of data in a ROM that identifies the original cartridge contents. On some consoles, the console manufacturer required they be included in the ROM. That is known as an "internal" header. Other times, it is added outside of the original ROM, for copier or emulator compatibility, those are known as "external" headers. No-intro only catalogs ROMs without external headers. The exception is made for the NES, since the external header is a necessity for emulation purposes (it which case it is ignored for checksum purposes).

Mappers: cartridge-based consoles had a limit to how much ROM the CPU could access. A "mapper" is hardware within the cartridge that allows more ROM than the limit, by only making a portion of the ROM accessible to the CPU at one time. Some consoles used those frequently (like the NES and GB, where over 95% of the library used them), others rarely (like the GBA, which I think only had a mapper in one or two GBA Video carts).

Banks: Related to the above, a bank is one section of the ROM, and is how much the mapper can switch at one time.

Checksum: a math function that verifies a ROM by adding the value of the bytes of the ROM in some uniquely identifying way.

777gamer
Posts: 15
Joined: 19 Nov 2015 03:05

Re: some cartridge question

Post by 777gamer » 02 Mar 2016 20:39

so the nes dumps got 2 headers?
ok thanks

KingMike
Posts: 404
Joined: 22 Sep 2012 16:36

Re: some cartridge question

Post by KingMike » 03 Mar 2016 06:45

NES ROMs only have the external header, not an internal one (why is why the external header is required for emulation, unlike other consoles like SNES and GB).

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