To appreciate this game, you'd probably have to be a fan of both Manic Miner and the ZX81. If you are, then this really is quite impressive.
Some time ago, Czech programmer Ales Martinik performed the almost unthinkable by porting Manic Miner to the vanilla 16K ZX81. This is really something quite special in itself. The most amazing thing is that it was managed at all given that the native, software-driven display of the ZX81 is strictly character mapped. The way around this limitiation is to replace the standard interrupt service routine of the ZX81 with a custom one which allows bitmapped screen bytes to be fetched from different locations of the ROM on a per-scanline basis. There is another limitation though, only about half of the possible 256 byte values happen to be available at relevant places in the ROM, meaning you have to just use a byte with a bit-pattern nearest the one you actually want. This means you may have a pixel or two in the wrong place. So this is not completely true freedom of pixel setting in the horizontal resolution. However it is true high-res in the vertical direction. Overall, this ZX81 screen mode is sometimes known as "pseudo hi-res" and is the only "hi-res" mode available on the standard machine without expanding it with additional graphics hardware. Other ZX81 games such as "Rock Crush" also use this mode.
Ultimately, nine of the original Manic Miner screens had to be dropped in the ZX81 port, leaving eleven screens to play through, but it seems the most familiar ones have been retained including at least "Central Cavern" and "Eugene's Lair". The room names have been translated into Czech in this version. I have no doubt that if this port were thought possible back in the day, the ZX81 could have enjoyed a commercial release, but it seems to me that the pseudo hi-res mode of the ZX81 was not fully exploited until a few years after the ZX Spectrum had already taken off, unfortunately limiting its utilisation to relatively small number of titles.
Fast-forward to 2003 and ZX81 and Speccy public domain developer Russell Marks takes the ZX81 version and ports it to the ZX Spectrum 128K. The impressive thing here is apart from some (non-intrusive) increased jerkyness due to staggered screen updates, it's pretty much indistinguishable from the ZX81 port. Russell notes in the embedded game FAQ that this port could be considered "pointless" but on the contrary I find it a worthwhile effort that as many as possible Manic Miner variants should be made available on the speccy platform. I'm sure Manic Miner fans who use a real 128K system could make use of this title. My limited understanding of how this version works is that it natively executes a patched copy of the ZX81 version on the Speccy's Z80. i.e. it doesn't actually emulate an entire ZX81 with CPU and all. However, the pseudo hi-res screen mode is emulated and this requires a significant proportion of the Speccy's CPU cycles, hence the need for staggered display updates. A 128K system is needed to run this according to the docs, as the 128K-only alternate screen is made use of while the ZX81 program code executes in the standard ZX Spectrum screen area.
As for the gameplay itself, the collision detection is a bit hairy to say the least, no doubt a limitation of ZX81 pseudo hi-res mode. This however makes the game pleasingly more difficult than the original speccy version, as at least it is consistently less forgiving. So for those of you who can do the original "Central Cavern" blindfolded, you'll find this version to be quite a bit more challenging than you are accustomed to. The game is based on the "Software Projects" re-release as apparently can be seen by the sprites in "The Warehouse" level, so Russell embedded a scanned copy of the Software Projects release tape inlay on the intro screen which is a really nice touch. The ZX81 version implements the "air indicator" as a numeric digit display rather than a decreasing horizontal bar which would be impossible to implement smoothly in pseudo hi-res mode. You'll also notice that as Miner Willy walks right and then left, the sprites are not an exact mirror image of each other. e.g. in one frame he has a "fat leg", again quirks of the pseudo hi-res mode. In the absence of a cycling colour palette, the keys which must be collected stand out instead by virtue of having flickering pixels. Despite all this though, the game incredibly manages to retain the look and feel of the original (within the obvious limitations that it is monochrome and silent), including very much the playability.
So overall, this title may not particularly appeal to those who aren't really interested in the technical details or those who don't wish to complete as many Manic Miner variants as is humanly possible. But if either of the above do apply, then definitely check this one out, above all else (given the limitations) it's good fun to play too!
