The มาร์ควัน had 60 sets of 24 switches for manual data entry and could store 72 numbers, each 23 decimal digits long. It could do three additions or subtractions in a second. A multiplication took six seconds, a division took 15.3 seconds, and a logarithm or a trigonometric function took over one minute.
The Mark I read its instructions from a 24-channel punched paper tape and executed the current instruction and then read in the next one. It had no conditional branch instruction. This meant that complex programs had to be physically long. A loop was accomplished by joining the end of the paper tape containing the program back to the beginning of the tape (literally creating a loop). This separation of data and instructions is known as the Harvard architecture (although the exact nature of this separation that makes a machine Harvard, rather than Von Neumann, has been obscured with the passage of time, see Modified Harvard architecture). The first programmers of the มาร์ค วัน were computing pioneers Richard Milton Bloch, Robert Campbell, and Grace Hopper.