each instruction was executed, the next one was just emerging from a Delay Line. The position of instructions in the store could greatly affect performance if the location of an instruction was not optimum. Reading data from the card reader was done in real-time – each row had to be read as it passed the read brushes, without stopping. Similarly for the card punch; the word for a particular row was prepared in advance and had to be ready when a given row of the card was in position under the punch knives. The normal mode of reading and punching was binary. Decimal input and output was performed via software. The high-speed store consisted of four single-word registers of 32 bits each, three double-word registers, and two quadruple-word registers. Each 32-bit word of the double and quadruple-word registers could be addressed separately. They could also be accessed as a pair, and—in the case of the quadruple registers—as a group of three or four. The instruction store consisted of twelve mercury delay lines, each of 32 words, and numbered 1 to 12. Delay line 11 (DL11) served as the buffer between the magnetic drum and the high-speed store. Being a "transfer machine", data could be transferred a word at a time, a pair of words at a time, and any number of words up to 33 at a time. Thus, for example, 32 words read from the drum could be transferred as a block to any of the other delay lines; 4 words could be transferred as a block from one quadruple register to the other, or between a quadruple register and a delay line—all with one instruction. The 32 words of a delay line could be summed by passing them to the single-length adder (by means of a single instruction). By a special link between DL10 and one register, namely, register 16, DL10 could be used as a push-down stack. Production The first three machines were delivered in the spring of 1955; in late 1958 a DEUCE Mark II improved model appeared. This version employed a combined card reader and punch. The combined IBM 528 reader and punch behaved like the separate Hollerith units on the earlier DEUCE Mark I machines; however, it was also provided with hardware conversion of alphanumeric data to BCD on input, and vice versa on output. Data could also be read in and punched simultaneously