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The ZX Spectrum version of Carrier Command has 3D rendering, while the Commodore 64 version, despite a greater amount of RAM, was inferior in comparison. You open the in-game map and there's Google Maps right there. Maybe the faster Z80 was the reason? Also, I've read 6502 and 6510 have no division, which you need for perspective division. This is not strictly a problem though, as you can have a lookup table of inverses, I suppose, and just multiply with these.

Here are the C64 and the Spectrum versions.

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    The clock speed is definitely a factor - the Spectrum was 3.5Mhz, a PAL C64 is 0.98MHz. Anything on the C64 that could not take advantage of hardware-based graphical features like sprites and pixel scrolling ran like a dog compared to the Spectrum\BBC Micro equivalents.
    – Alan B
    Oct 30, 2021 at 12:41
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    You can implement integer division in software with a loop over the bits (involving extended-precision left shift of rem:quot, compare, and subtract). Not super fast, especially for 16-bit integers on an 8-bit machine (it needs a compare instead of a single-bit test, so you need more full-width operations than multiply via shift-and-add, but otherwise pretty similar). How can I multiply and divide using only bit shifting and adding? shows how in C and x86 asm. Oct 30, 2021 at 18:33
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    @AlanB _"the Spectrum was 3.5Mhz, a PAL C64 is 0.98MHz" - but the Z80 has minimum 4 clocks per instruction while the 6502 is 2, so the difference isn't as great as your numbers suggest. retrocomputing.stackexchange.com/questions/5748/… Oct 30, 2021 at 19:25
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    @AlanB Clock speed of a CPU is only comparable with CUs of the same design. Even more important for simple 8 bit CPUs like Z80 and 6502, Performance is all about memory speed and here both systems are rather close.
    – Raffzahn
    Oct 30, 2021 at 21:03
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    Why are we assuming there's a technical reason? The ZX Spectrum version of Hard Drivin' is about a million times better than the C64 version too, but primarily because the latter was a last-minute botch job. Ditto the Spectrum version of R-Type is more accurate to the gameplay features of the arcade because the C64 version is a reskinned Katakis, for entirely business-related reasons.
    – Tommy
    Oct 31, 2021 at 0:55

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The Spectrum version of Carrier Command was for the ZX Spectrum 128 only (reference: Carrier Command (World of Spectrum)). This was probably crucial in being able to port it so well.

Neither the Z80 nor the 6502 had division (or multiplication) commands.

Another reference for the Spectrum port being 128 KB only is the review from Crash magazine, issue 63.

Addition: In Retro Gamer magazine, issue 111, pp46--51, there is an article "The Making of Carrier Command". Here it says that the Commodore 64 version was added to the agreement (between developers Realtime Games and publishers Rainbird) later to replace the cancelled PCW version, and that development of the C64 version was outsourced to developers Source. Meanwhile, the Z80 versions (Spectrum 128 and Amstrad CPC) were developed in-house by Realtime Games, and the company already had considerable expertise in 3D on the Spectrum, having developed Starstrike II and ported Starglider.

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