[HEADER] [COUNT] [FILE INFO 1][FILE DATA 1][FILE INFO 2][FILE DATA 2][FILE INFO 3][FILE DATA 3], repeated for as many files as it has.
Maybe a disk copier only copies the N files the disk says it has, ignoring the invisible files.
the first interesting thing is that files have a number and an ID code, and work differently. number is just 0, 1, 2, 3 on the disk,but IDs can be anything, except that there's a "boot ID" field in the header, which determines which file is loaded first.
if that's the case, why not just boot the one with the lowest id? I'm not sure.
Files can only be up to 64k in size, which isn't a problem because the disk itself only stores ~64-84kb a size, and the header and lead-in take up at least 26k of that.
This tells the BIOS where in RAM to put the file when loaded.
There's a type-of-RAM field because the RAM Adapter has two types of RAM, in addition to the 2K of ram in the famicom itself.
the kernal would read the first two bytes and use that to determine where in RAM to stick the loaded data, instead of at a standard location.
Depending on if this is a fresh disk or a rewritten one, it can know it costs between 500 and 3400 yen.
So if you brought in a disk to Nintendo, they could figure out which store you bought it at.
This isn't out of character for Nintendo: unless you've hacked or painted them, your Switch Joy-cons know what color they are.
The date and the country.
except I lied. it doesn't use the 6502. You'll often see it listed as using the 6502...
These days computers usually start from 1970, and count seconds or milliseconds since.
This is a traditionally used system which dates years by the emperor who reigned during them. the Shōwa era started in 1926, and they don't have a year-0, so 1926 is Shōwa 1.
OK. That doesn't seem that weird, just not the sort of thing non-Japanese people would know about.
So the system is based on Shōwa era dates, and the Shōwa era ended only 3 years later in 1989.
Hopefully, on April 30th, Emperor Akihito will abdicate, Crown Prince Naruhito will take over, and we'll begin the Reiwa period
So we're onto the last, finally bit of silliness in the disk header.
Presumably this could be used for some kind of region coding? or possibly to select different language versions of the firmware, or similar.
And all (legitimate) famicom disks were made in only one country, Japan.
or 73. Yeah, it's 73. I don't know why it's not just 1, or 0, but it's 73.
You'll commonly see it quoted as 64k a side, but that's just a round number, and one that's known to be wrong.