Hardware Test: Pentagon

Hardware Test: Pentagon

From: L. C.

(Note: This text was translated automatically by a PC translator program, so sorry if there are many mistakes.)

Contrary to the April fool hoax 'Pendragon', the Pentagon actually exists, and I have already received mine. Let me say right away: anyone expecting a professional-looking computer will be sorely disappointed. For 150 US dollars, you get the following: one Pentagon with a 5.25" drive and keyboard. Note that the power cord must be changed to our standard or replaced.

On the desktop-plexiglas case sits the Pentagon mainboard, which—apart from some cables and 'dead chips' (soldered the wrong way round)—looks quite professional. The central processing unit must be inserted by yourself before the fun can start. There are some interrupted connections on the board, but without them, the picture would be all blue or another color. The truth is that the Pentagon consists only of a professionally prepared board, self-mounted by Zhenya.

It is interesting that turbo-modifications and memory expansion up to 512K are possible (nothing unusual if one considers that a Spectrum 128 with a fully extended MB02 reaches 640Kb and even higher speeds with DMA). For the turbo mode, the Z80A must be replaced with a Z80H.

Above the board sits an AY sound interface, further behind it the disk/tape/printer interface with some unknown outputs, and presumably some memory expansion slots. The top of the case is easily removable. Zhenya was nice enough to rearrange the RGB output so it no longer inverts the picture; however, the monitor output is not in its planned space and hangs freely in the air.

Keyboard and Exterior

The keyboard is held by plastic holders and conforms to our standard regarding the letters, though in appearance it reminds one of an old 48K rubber keyboard. The keys are arranged in lines, splitting right and secondary, under each other. The keyboard is detached from the main case and is the most professional-looking part of the Pentagon. Since this part didn't work well for me, I have been using a DK'Tronics keyboard instead. The cable itself is probably two meters long due to the missing ULA.

A 5.25" 720Kb drive is built-in; there is space for an additional 3.5" or a second 5.25" drive. Behind the drive sits an over-dimensional power supply. It also has an extra-large capacitor to stabilize fluctuations in the AC supply, which is necessary in Russia. Two over-dimensional coolers are attached externally to the rear, serving to heat the room. Inside, there is also a large cooler, which acts as a holder for the 3.5" drive power supply.

On the back, we find the two coolers with two voltage regulators each, two tape ports in DIN format, a printer port (Sub-D 25-pin), a fuse, a power supply line, and the RGB port (R, G, B, Composite Sync, Gnd, Snd, all in one DIN terminal). I suspect it says 'KGB' instead of 'RGB' because of the small labels, but surely KGB traps are more mature than mousetraps!

On the front, you'll find the drive, power switch, a 5-pin DIN joystick connector, a 7-pin DIN with an unknown function, a 16-pin connector (surely for an external keyboard!), and three plexiglass buttons for reset.

Technical Details

Inside, you notice the absence of a ULA and the strange internal construction. The mainboard only has one plugging connection—an expansion port that provides electric energy. The TR-DOS 5.03 is fixed in the ROM. The sound interface is also on an external board. The absence of the ULA IC has the pleasurable effect that the storage area from 16384 to 32767 is not slowed down, allowing the I-register (interrupts) to be set to a value under 128 without the 'snow effect', which is why many Russian demos run correctly.

Testing

I quickly built a Pentagon RGB to SCART interface and plugged it in. The first thing I noticed was that the menu had no tape loader option; instead, it featured 48K TR-DOS and 128K TR-DOS selection. After finding the manual, I discovered that for TR-DOS 5.03, the correct address to jump to DOS is 15616 (15619).

After selecting TR-DOS, the Speccy tries to load the autostart file from the disk. I played Prince of Persia, where I noticed a slight glitch in the video chip: a pixel column from the center of the left screen half was displayed additionally after the left-most pixel column.

Performance

I also tested the well-known Ecstasy Megademo (which shows 100-102% performance, whereas the normal Speccy only reaches 96%). The Pentagon part didn't run at first, but the 'Magic Fly' and subsequent parts ran at full 50 fps! A great new feeling! Most parts run twice as fast as on the 128K Speccy, 'Magic Fly' even three times as fast.

Where to Buy

The Pentagon can be bought for 150 US dollars from:
Dalnikovas Eugenijus
Kalvariju G. 142-3
2042 Vilnius / Lithuania

I sent the money by hiding the dollars inside a defective 5.25" disk, sent as a registered letter. It worked perfectly. If you want to watch Russian demos or just want a faster Spectrum 128, order a Pentagon as soon as possible. It is currently the fastest Spectrum generally available.