Hardwaretest: PENTAGON

Hardware Test: PENTAGON

By: L.C.D.

Unlike the April Fools' joke Pendragon, the Pentagon actually exists, and I have already received mine. Right off the bat: anyone expecting a professional-looking machine will be bitterly disappointed.

For 150 US Dollar you get the following: 1 Pentagon with a 5.25" drive and keyboard. Though the power cord needs to be brought up to our standard with a small saw. Inside the desktop plexiglass casing is the Pentagon mainboard, which looks professional except for a few wires and "dead chips" (upside down on the board). You have to plug the CPU into its socket yourself before the fun can begin. There are some cut traces on the board, but without them the picture would be completely blue or in another color. The truth is that the Pentagon consists merely of a professionally made PCB that was populated by Zhenya himself.

Interesting in this context is that turbo modifications and memory expansions up to 512K are still possible (nothing unusual considering that a Spectrum 128 with a fully expanded MB02 reaches 640 Kb and achieves even higher speeds when utilizing DMA), but for the turbo mode you have to replace the Z80A with a Z80H. Above the board itself there is an AY sound interface, further behind and above that the disk/tape/printer interface with some ports I don't know and which presumably function as memory expansion slots.

The top of the casing is easily removable. Zhenya was kind enough to rewire the RGB output so that it no longer produces an inverted picture; for this reason, the monitor socket does not sit in its intended place but hangs freely in the air. The keyboard is held by glued-on plastic mounts and cross braces; it corresponds to our standard regarding the letters, but visually resembles an old 48k rubber keyboard. The keys in their rows and columns are arranged in straight grids next to and below each other and combine all keywords; only the EXTEND+SYMBOL keywords were printed below the keys. The keyboard itself is the most professional-looking part of the Pentagon, however it is not separate from the computer, but mounted in the front left corner, and the upper case top has the corresponding cutout at this spot. Since this part of the computer refused to work properly for me, I installed a DK Tronics keyboard instead. The cable itself can probably, due to the missing [...], be over two meters long.

A 5.25" 720 Kb drive is built in, but there is still room to install a 3.5" or a second 5.25" drive. Right behind the drive, an oversized power supply tries to hide, though frankly it doesn't succeed; the voltage regulator stage also turned out a bit too large, but at least there is a current display, something that is necessary in Russia in case power fluctuations occur in the mains. But Russian nuclear power plants don't explode that quickly. Thanks to the extra-large capacitors, any power fluctuation should be ironed out.

Two oversized heatsinks are mounted on the outside rear and probably serve to heat the room. Both are more than twice as large as was the case with the original Sinclair 128, but get just as hot during operation. Inside, there is also a heatsink of the same size, which serves as a bracket for the 3.5" drive rectifier stage. There is a fuse device on the transformer, but it was bypassed, because with its four voltage regulators you would probably have to buy a larger batch of fuses right away.

Since a few things broke during transport by the postal service (the post? they are total destroyers), I had to replace some poorly glued spots with screws, but for a good drill, plexiglass is no problem at all.

At the rear, as already mentioned, are the two heatsinks with two voltage regulators each, two tape ports in DIN format, printer port (Sub-D 25-pin, female), fuse, mains connector, and originally also the RGB output (R,G,B, Composite Sync, Gnd, Snd all as DIN 5-pin). At least I suspect it was intended for the RGB output, because it only says KGB, but they definitely don't have agents that small, and KGB traps ought to be far more sophisticated than mousetraps?

On the front, the drive catches your eye first, then there is the power switch and a strange 5-pin joystick port according to the DIN standard. Right next to it, another DIN connector, only this time 7-pin with unknown function. Then follows a 16-pin connector whose function is likewise unclear to me (almost certainly external keyboard!) and three plexiglass pushbuttons, one of which serves as Reset.

Inside, the first thing that strikes you is that there is no ULA at all, along with the unusual layout: the professional-looking PCB has only one plug connection, namely an expansion bus through which it is supplied with power. The DIN tape ports are also built on their own board. The disk interface itself gets by with so few components that I believe the main part of the disk interface is located on the mainboard. In any case, TR DOS 5.03 is permanently built into ROM. The sound interface is also plugged into an external board. The absence of a ULA IC has the pleasant effect that the memory area 16384 to 32767 is no longer slowed down, and thus one can also set the I register (interrupts) to a value below 128 without this annoying snow effect occurring, and so finally many Russian demos run properly.

All right, time to test the Pentagon: I quickly built myself a Pentagon RGB to SCART interface and plugged the Pentagon into a socket (Whoops, the power switch has no function at all!). No stable picture! After some tinkering which I will present soon, I finally had a nice picture with proper brightness, and the first thing I noticed on the menu—which looked so typical of a 128 at first glance—was that there was no Tape Loader option at all, and furthermore the tape tester was replaced; instead, one can now choose 48k TR DOS and 128k TR DOS (where on earth did I leave that sh... damn$%&@! TR DOS manual? I still had it a few days ago!).

A few hours later I found the manual and the time to get the power switch working, so the actual testing could now begin. Unfortunately, I only have the manual for TR DOS 4.0, but version 5 is inside the Pentagon; probably because of that I couldn't jump into DOS with USR 15360. The correct address for TR DOS 5.03 is 15616 (15619).

After selecting the respective TR DOS from the main menu, the computer tries to load the autostart file from disk, and I was smoothly able to play Prince of Persia; doing so, I noticed a small flaw in the video circuitry, as a pixel row from the middle of the left half of the screen is additionally inserted after the leftmost pixel column.

The other disks I received were, besides the already mentioned Prince of Persia which is copy-protected, 15-teens, a number puzzle game with picture tiles. If you slide everything correctly, you are rewarded with a little animation, mostly of pornographic content. The individual levels are loaded from disk (kind of neat!).

Then there were disks with demos and games rewritten for Pentagon, including Ecstasy Megademo, already known from SCENE+ (shows 100 to 102% performance, while the normal Speccy only manages 96%). Interestingly, the Pentagon part still doesn't run, but the Magic Fly part and the subsequent one run as fast as they are supposed to, meaning 50 FPS! A completely new feeling! Most parts run twice as fast as on the 128k Speccy, MAGIC FLY even three times as fast!

At the Cologne meeting I once compared the Spectrum 128 and Pentagon Ecstasy demos to show those present how much difference a mere 4 to 6% makes!

I still need to ask Zhenya about the turbo mod and 512Kb expansion, but for that I would have to swap the existing Z80A for a Z80H; unfortunately, Austria is so backwater that I've never seen a Z80H in any shop!

For comparison: my AMD K6 200Mhz gets the emulator up to 2173% of the normal speed of a Spectrum, which is a Spectrum at 74Mhz! Yet I only reach the speed of a Pentagon with a 200% setting; strange, because the Ecstasy demo displays significantly lower speeds.

You can order the Pentagon for 150 BillGatesDollar from:

Dalnikovas Eugenijus
Kalvariju g. 142-3
2042 Vilnius/Lithuania

How I handled sending money to a country where not everyone respects the property of others, you can do it the exact same way: I sent him a letter announcing that the next letter would contain a defective 5.25" disk, inside of which I had hidden the dollars. Then I sent off this second letter with the floppy disk as a registered letter (Registred). This way there were no problems. Of course, you shouldn't just slit open the disk, otherwise even a blind man would spot the tampering; rather, you should take care to fold the banknotes and slide them in through the existing center hole. With a little luck, it looks from the outside like a completely normal floppy disk.

Anyone interested in Russian demos and games or who simply wants to get to know the somewhat faster Spectrum 128 should order the Pentagon as quickly as possible. It is currently the fastest Spectrum of all.

One shouldn't indulge in the false hope that Russian coders will write programs that also run on a normal Spectrum when they already have the Pentagon's capabilities at their disposal, and honestly: if the Russians had a Speccy with only 2 MHz, would we give a damn about that? Think about it!

Have fun if you want a Pentagon too!

Yours, L.C.D