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238 votes
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How did Commodore's anti-Microsoft Easter Egg work?

I'm the author of the TPUG article. The "BILL GATES SUCKS" message isn't really an Easter egg; that was just a conceit of mine to make the article a bit more interesting and to turn it into a bit of ...
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97 votes
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Why is EEPROM called ROM if it can be written to?

Look at the development: ROM = read-only memory = can only be read when on the board, programmed in the chip factory. PROM = programmable read-only memory = can be programmed with a special programmer,...
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63 votes

How did Commodore's anti-Microsoft Easter Egg work?

That's not a real easter egg. Someone just made an effort to find random seeds that produce the numbers to create the intended words. It would be an easter egg if the seed numbers were in some way ...
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39 votes

How do arcade ROMs work

The way I understand it, ROMs are like virtual games, Not really. ROMs are a piece of hardware storing a bit image. Like a disk, a tape or a punch card. It holds an image of the game's software. ...
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  • 173k
31 votes

Algorithm for Apple IIe and Apple IIgs boot/start beep

What is algorithms use for boot/start sound (when turn on computer) Algorithm? Well, yes, technically everything is an algorithm. In this case it's simply executing the beep subroutine during reset, ...
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  • 173k
31 votes

Why is EEPROM called ROM if it can be written to?

EEPROM can't be "written to." It can be programmed. Programming is different. When there's EEPROM in a CPU's physical address space, ordinary write cycles will not affect it. Something out ...
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30 votes
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What is the relationship between solid-state ROM and inaccessible content in arcade games?

Excess capacity. ROM chips come in standard sizes based on powers of 2 and it is quite unlikely a particular size will be exactly what a game needs. For example, suppose a game displays numbers that ...
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27 votes
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Why would older video games include fragments of source code?

I'd guess a lot of the systems used for development didn't clean the memory down in between usages. It's also likely that for games "gaps" got left between binary chunks. So if for a hypothetical ...
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  • 5,155
22 votes

Why did POKEing ROM addresses mask port writes?

The following is an excerpt from the article César Hernández Bañó and I wrote about the internals of the Inves Spectrum+, exposed after a detailed work of reverse enginnering. First, some background: ...
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21 votes
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How do arcade ROMs work

The other answers already covered a lot, but there is something else that is important but which hasn't already been addressed in detail: Despite appearances to the contrary, arcade machines are ...
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20 votes
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Did the Apple 1 cassette interface card have its own ROM?

The Card featured 256 bytes of ROM. Is there evidence documenting how the cassette program was stored? The evidence is right there in the PCB photo you added. The two MMI 6301 chips, labled APPLE A3 ...
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  • 173k
19 votes

How can a Game Boy game "glitch-inherit" the music from a different game like this?

I don't know if this is correct, but it seems to fit. The SNES sound chip is a full processor. It can run its own program and play sounds independently of the main processor. It is also possible for ...
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17 votes
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Does an Apple //e actually have 64KB of RAM?

The original Apple II has up to 48K of RAM from $0000 to $BFFF and 10K of ROM between $C000 and $FFFF except for a hole between $D800 and $DFFF. You can get a language card which puts 16K of RAM under ...
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17 votes
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Best way to locate data on ROM? (6502 Processor)

I've done this partially with Commodore PET Space Invaders which I used as a test program to debug my Commodore PET emulator. I used a disassembler to convert the program to assembly language and I ...
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17 votes
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Does fast page mode apply to ROM?

Does fast page mode apply to ROM? No. Why should they? You're missing one step to start with in your chain of thoughts. (Fast) Page Mode is an improvement to the address multiplex protocol dynamic ...
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  • 173k
17 votes

Can you read the character definitions (font) in an Apple II using PEEK in Applesoft BASIC?

No, it's not possible to read the built-in text mode font data from "inside" the machine. (Update: Except perhaps in the Apple IIgs - see below.) In all Apple II models the font data is in a ...
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16 votes
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What did the Supercard "patch" program actually do to GBA and NDS ROMs to make them playable?

The GBA's memory controller can be configured using WAITCNT, an MMIO port at 0x04000204, to use slow or fast timing when accessing the Game Pak slot. The BIOS boots up in slow mode, in case Nintendo ...
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16 votes

Why would older video games include fragments of source code?

I don't know if this applies in every case, but, on the Commodore PET and by extension C64, an executable program file on disk/tape consisted of a load address (normally $0401 on the PET) and then ...
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16 votes

Why is EEPROM called ROM if it can be written to?

It can't be 'written to' in the sense of storing useful information written by a running program in the computer. It can be erased and re-programmed, which generally requires a special ROM programmer (...
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  • 28.3k
15 votes

C64 cartridge emulation with ATmega

As a personal project I had the idea to create a custom cartridge for my Commodore 64 and use an ATmega 1284p microcontroller to emulate eproms and/or custom chips. I doubt that this will work! The ...
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15 votes

Why are there no actual complete and 100% verified/vetted ROM collections still?

You've answered your own question: this is a thankless and massive undertaking they of course can never make any money from it it's very illegal to make these available, which also puts them in ...
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14 votes
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What does it mean to byte swap or split a ROM image?

Splitting the ROM is not the same as byte-swapping the ROM. Amiga ROMs are usually split so that odd locations and even locations are stored in separate chips. This is because the 68000 has a 16-bit ...
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13 votes
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Maximum size of 8-bit computer cartridges

Simple Answer: Unlimited and Many Ofc, every system can only reserve a certain amount of real address space for cartridges, but then there is Bank Switching. Just take the original Atari 2600. ...
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  • 173k
13 votes

Decoding Logic and Memory Systems for 8-bit computer - 64K address space

Your observation about the 64K address space is correct, your 32K RAM and 32K EEPROM will be able to fill that address space to 100%. In Z80 designs, the ROM/PROM/EPROM/EEPROM is usually placed ...
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12 votes
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What kind of EPROM was used for the Apple //e character generator, and how do I write a new one?

The standard US Apple //e Video ROM was pin compatible with 2732 (4k) EPROMs, but some foreign models (UK, German, French, Italian) used a 2764 (8k) compatible ROM with two character sets. Your clone ...
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12 votes

What does "ByteSwapped" and "BigEndian" refer to in the context of video game ROMs?

There’s a detailed thread about this on Jul. Basically, there are three data storage orders used for Nintendo 64 ROMs: big-endian, which is the Nintendo 64’s native order (Z64 in the thread); little-...
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11 votes

Arcade games in Apple IIc's ROM

I feel like you're remembering the Apple At Play disk that came with the Apple //c. It had Lemonade Stand, Quick Quiz, and Space Quarks (more of a Galaxian clone than Space Invaders, but I didn't ...
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11 votes

Historical price of ROM

You can get a sampling of prices for EPROMs the hard way, by checking ads from electronics magazine archives. For example on page 116 of Popular Electronics Jan. 1977 you can see the 1702A 2K(bit) ...
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