The first thing Dennis worked on was an assembler. This was something that translated assembly language--which used three- letter symbolic abbreviations that represented instructions to the machine--into machine language, which consisted of the binary numbers 0 and 1. The TX-0 had a rather limited assembly language: since its design allowed only two bits of each eighteen-bit word to be used for instructions to the computer, only four instructions could be used (each possible two-bit variation--00, 0 1, 10, and 11--represented an instruction). Everything the computer did could be broken down to the execution of one of those four instructions: it took one instruction to add two numbers, but a series of perhaps twenty instructions to multiply two numbers. Staring at a long list of computer commands written as binary numbers--for example, 10011001100001-- could make you into a babbling mental case in a matter of minutes. But the same command in assembly language might look like this: ADD Y. After loading the computer with the assembler that Dennis wrote, you could write programs in this simpler symbolic form, and wait smugly while the computer did the translation into binary for you, Then you'd feed that binary "object" code back into the computer. The value of this was incalculable: it enabled programmers to write in something that LOOKED like code, rather than an endless, dizzying series of ones and zeros. The other program that Dennis worked on with Stockman was something even newer--a debugger. The TX-0 came with a debugging program called UT-3, which enabled you to talk to the computer while it was running by typing commands directly into the Flexowriter, But it had terrible problems-for one thing, it only accepted typed-in code that used the octal numeric system. "Octal" is a base-eight number system (as opposed to binary, which is base two, and Arabic--ours-which is base ten), and it is a difficult system to use. So Dennis and Stockman decided to write something better than UT-3 which would enable users to use the symbolic, easier-to-work-with assembly language. This came to be called FLIT, and it allowed users to actually find program bugs during a session, fix them, and keep the program running. (Dennis would explain that "FLIT" stood for FLexowriter Interrogation Tape, but clearly the name's real origin was the insect spray with that brand name.) FLIT was a quantum leap forward, since it liberated programmers to actually do original composing on the machine--just like musicians composing on their musical instruments. With the use of the debugger, which took up one third of the 4,096 words of the TX-O's memory, hackers were free to create a new, more daring style of programming.