The Pentagon 48K takes its name from its circuit board, which has a diagonal cut across one corner and so has five sides. It was a clone of the Sinclair ZX Spectrum from 1989, built by amateurs in the Soviet Union with no manufacturer behind it.
Why it matters
The Pentagon was never sold as a finished product. It was a board design, and people copied it: English Wikipedia records that the PCB was duplicated all over the former USSR between 1991 and 1996. The same article names Vladimir Drozdov as the designer of the 48K, though Russian Wikipedia says the early history is poorly documented. A 128K version followed in 1991, and the family ran on to the Pentagon 1024SL in 2005. The 48K ran Spectrum software on Soviet Z80 clones and discrete logic, with a frame of 71,680 T-states against the Spectrum’s 69,888.
What to check before you buy
- Ask whether it is a period build or a modern reproduction kit.
- Confirm which variant you are getting: 48K, 128K or a later board.
- Ask whether a Beta 128 disk interface is fitted, and whether it works.
- Test with timing-sensitive software, because the non-standard frame timings can break some titles.
- Expect no documentation or provenance.
