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zk/ROM versus disk loading.md

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+---
+id: rmvm
+title: ROM versus disk loading
+tags: [computer-architecture, memory]
+created: Monday, June 24, 2024
+---
+
+# ROM versus disk loading
+
+I will explore the concept via the practical examples of cartridge-based and
+disk-based video games console.
+
+When you insert a disk into an Xbox, the game data is typically read from the
+disk and transferred into the console's memory by the OS. If the game is
+installed to the hard drive, this initially involves transferring substantial
+amounts of data to speed up future access. When you insert a cartridge into a
+console like the SNES, the data is not transferred in the same way. Instead, the
+cartridge contains a ROM chip that, when inserted, integrates directly with the
+motherboard. From the operating system’s point of view, this ROM chip behaves as
+an extension of the system’s memory architecture.
+
+The primary advantage of a ROM-based game is significantly reduced latency. The
+game data can be accessed as rapidly as any other data moving along the buses of
+the motherboard. With a disk, the data must first be read into a buffer and then
+transferred to a memory address where it can be accessed by the CPU.
+
+With a ROM, while the console CPU still uses its own RAM to run the game
+(similar to disk-based systems), the game data on the ROM can be loaded into
+this RAM more quickly because it is directly attached to the motherboard. This
+makes the ROM cartridge effectively a fast, directly connected storage device.
+
+However, despite its speed, the limitation of a ROM cartridge is its storage
+capacity—it can hold only as much data as the chip can accommodate. In contrast,
+a disk can store much more data. This larger storage capacity allows not just
+for bigger and more complex games but also for the possibility of expanding the
+game through additional data downloaded to the console's hard drive. Such
+expansions or patches represent additional data from the console’s storage that,
+combined with the original disk data, are synthesized in memory at runtime for
+enhanced or updated gameplay experiences.
+
+(Note however that modern cartridge-based consoles like the Nintendo Switch can
+also combine ROM-data with expanded data from the console HDD, sourced from the
+internet.)
+
+Both disks and ROMs are forms of static storage in the context of a game
+console. While disks can technically be overwritten with new data, in practice,
+manufacturers implement various locks and protections to prevent this. Any
+changes or additions to the game, such as patches or expansions, are not written
+back to the original disk. Instead, these updates are stored on the console's
+hard drive.
+
+Therefore, if you download an expansion for a game on your Xbox, the original
+disk remains unchanged as when you first purchased it. Consequently, if you were
+to take that disk and load it on another Xbox, it would not include any of the
+expansions or updates. The game would function in its original form, as the
+additional content and updates reside solely on the hard drive of the first
+console where they were downloaded.
+
+## Related notes