Another New Old Computer on an FPGA

How would you sell a computer to a potential buyer? Fast? Reliable? Great graphics and sound? In 1956, you might point out that it was somewhat smaller than a desk. After all, in those days what people thought of as computers were giant behemoths. Thanks to modern FPGAs, you can now have a replica of a 1956 computer — the LGP-30 — that is significantly smaller than a desk. The LittleGP-30 is the brainchild of [Jürgen Müller].

The original also weighed about 740 pounds, or a shade under 336 Kg, so the FPGA version wins on mass, as well. The LGP-30 owed its relative svelte footprint to the fact that it only used 113 tubes and of those, only 24 tubes were in the CPU. This was possible, because, like many early computers, the CPU worked on one bit at a time. While a modern computer will add a word all at once, this computer — even the FPGA version — add each operand one bit at a time.

The LGP-30 had a Friden Flexowriter (a TeleType-like machine made by a company eventually bought by Singer, the sewing machine company) and a magnetic drum with 4096 32-bit words. To keep the component count down, the drum stored the program, the CPU registers, and even the 120 kHz system clock. There were also 1,450 solid-state diodes, which helped. To avoid building a lot of blinking lights, the front panel had an oscilloscope that displayed three registers. There were about 500 units sold for about $47,000.

The FPGA version — mercifully — is less expensive. It uses a Xilinx Spartan 6 development board and a custom PCB that even duplicates the oscilloscope on an LCD. You might notice some strange characters on the oscilloscope. Even though the computer used hexadecimal (which was unusual in those days), it did not use A-F for the extra digits. Instead, it used characters that were easier for the limited hardware to decode: f, g, j, k, q, and w. So 255 in LGP-30-speak is ww not FF.

Although the FPGA version is faithful, inexpensive, and small, it isn’t the first solid-state version of the architecture. Librascope — the company behind the LGP-30 rolled out the LGP-21 in 1963 which had less than 500 transistors and 300 diodes. It wasn’t as fast as the LGP-30, though, and cost a measly $16,200. Then again, the FPGA board costs less than $40 although the front panel and case will move that price up, it is still going to come in well under that price. If you want a peek inside the real machine, check out the video below.

Any time we see bit-serial CPUs, it reminds us of EDSAC. One thing that was interesting to us was that a 113 tube machine would have been within reach of the day’s hackers if they’d had the plans. In 1967, for example, people did build the Wireless World Computer with around 400 transistors.

Filed under: classic hacks, FPGA