NASA tried to correct its tendency to underestimate memory size, but was disappointed again on the Shuttle program. One requirement for memory was that it be large enough to contain all the programs necessary for a mission. Therefore, memory estimates became a regular part of preliminary design studies. Most estimates in the 1969 to 1971 period ranged around 28K words46. Rockwell International settled on 32K in its bid and won the contract partially because of that estimate47. NASA, trying to save itself from later difficulties, bought 64K of memory for each computer, hoping that doubling the estimate would be enough (despite memory increases in previous programs of several hundred percent)48. Unfortunately, the software grew to over 700K, requiring not only more computer memory, but the addition of mass memory units to hold programs that would not fit into the extended core. Parten said after this, "I don't know how you ensure proper memory size ahead of time, unless you're incredibly lucky"49.
From the standpoint of a spacecraft designer worried about power requirements, an interesting feature of the AP-101 memory is that only the module currently being accessed is at full power. If a memory module is used, it remains at full power for 20 microseconds.  If no further accesses are made in that interval, it automatically goes to medium power. If the entire computer is in standby mode, it goes to low power. An estimated 136 watts are saved by doing this switching50.