Actually, the input bit is interesting as well. The physical machine was like a big desk with a typewriter (a proper cast-iron 50s-style typewriter, no fancy terminal stuff here), but there really was no interfacing at all. The keyboard was connected exactly like (and in parallell to) the tape reader, which meant that when you pressed a key to input something, what you got was raw keycode rotated into the bottom bits of the accumulator. The machine could read 4- or 6-bit height paper tape, but 4 did fit the data model better, since you're aiming at filling up the accumulator with 32 bits of data (if reading a program in, or something). Otherwise, you'll waste the first 4 bits of the first 6-bit block. That is also why they talk about the program "only existing in hex" - You wrote the code on your notepad, and then you had to translate it down to paper tape 4 bit blocks - Hex. Which you'd probably punch to tape at a dedicated tape punch station, so as not to waste valuable computer time with slow human input. But I digress.
If you had the machine switched to 4-bit reception, the 0-9 keys on the keyboard actually generated the bit patterns 0000-1010, which is a good thing (although the keyboard didn't have a 1 key - you had to use lowercase L). Due to the wiring of the keybed, you had to use F, G, J, K, Q, W for the 1011-1111 patterns (or something else, since 4-bit meant that different keys would generate the same 4-bit pattern), but still, there was a way to input self-parsing data. If you wanted to input actual textual information, you had to use 6-bit to be able to differentiate between different keys, but then you lost the correspondence to the data, because 6-bit added bits to the least significant side of the pattern - 0000 (for 0) became 000010, for instance. So if you used text input, you got an accumulator filled with 6-bit patterns that had no discernible connection to the data they might represent.
The machine also showed the state of the registers while running...by displaying the voltage pattern from the register read heads on an integrated oscilloscope.
Actually, the story of Mel says that the story happened with the successor to the LPG-30, called the RPC-4000. That was certainly a more advanced machine - 8000 words on the drum, double accumulators, an index register, and 5 bits for operands, which means an instruction space of 32 instructions (which is actually 33-ish, since they are faking it a bit by reusing the bit pattern for Halt for another instruction, depending on the state of some other bits). And it does get to be a bit more competent - Even if most of the new instruction space is swallowed by the need to have double the amount of arithmetic operators for the dual accumulators, there is still space for explicit comparisons (>, <, =) and a jump based on them. Also, indexed fetch-from-memory, and some facilities for sensing the state of the machines control panel. The new word format also had an explicit jump at the end of each instruction - Each instruction consisted of the instruction itself, the adress of the data for the instruction, and the adress of the next instruction, all packed into one word. Apparently, Mel had learned his ropes on the LPG-30, and didn't want to change much
However, I'd say that I'd have problems making a blackjack program even on the more advanced RPC machine.
Somewhere, I found out that some guy wanted to run his LPG-30 programs on the PRC-4000, and actually wrote an honest-to-god LPG-30-
emulator for the thing, so that you could run LPG-tapes unchanged. That must mean that he was one of the very first emulator developers. It also gives some perspective to when people complain that this'n'that emulator doesn't reach full framerate
