Thanks for the Memories!
One of the few benefits of getting old is that you can recall being there as all this stuff actually happened.
In relation to the 640K memory issue, you of course realize, that at the time when young Billy Gates was initially contracted to write the IBM Disk Operating System (IBM-DOS), IBM was only able to source Motorola 64K Memory Chips.
The whole personal computer project concept, was to build and source a computing platform, that utilized market proven "off the shelf" component and combine them into a new design. This is why IBM chose to use a proven SIPP based chip that were already being used successfully in the Commodore PET & 64 and also by Sinclaire Electronics.
Gates despite his denial of ever saying
"That 640K of memory would be enough for anyone", did at the age of only 26. reason that his if he built an operating system that could address up to 10 fold the amount of available memory (10 x 64K), that am operating system would be remain current long enough for home users to become familiar it.
This was the premise that IBM based the launch of their personal computer on.
Gates also reasoned, that it would only be a matter of time before we would see 128K computers and as even the previous 64 standard had been derived by extending the 8k Memory chips of the mid 1970's x eight times.
Even with an OS that could address 640 K of memory most the
original 1981 IBM users could not afford the full memory (640K) models. Most of the first wave of some users settled for PC's that ranged between 128 to 512K.
Look at all that on board (hence the term), 64K memory Chips!Right up until the time that Compaq, NEC and others, that were known as Clone manufactures, entered the market in the Mid 1980's, could the average home users consider owning a full 640K XT Personal Computer.
All of this stuff was also expensive. I recall as late as 1990 having to get the approval of the manager of a Brisbane radio station to upgrade a PC to just 16 MB. The original AT 12 Mhz PC cost some $1400 and the memory (by now on a 30pin SIM), cost about $100 per MB for 4 x 4MB Modules of Motorola Parity RAM.
In other words the memory by itself cost $200 more than the whole PC.
As I site here writing this and are looking around my workshop, I still think I may have some of these modules here somewhere. At that price I could never bring myself throw them away (.... just in case they ever come back in to demand).

If you really fancy yourself a good "code cutter" and want to talk about lean mean software - take a look at the spec for the
Primary Guidance system that took Apollo around the moon and back. It ran a "blinding" 2.027 MHz and at it's disposal an awesome 2K of magnetic core memory.
It would have taken the combined storage of 35 of these unit to even store this image of the unit.Tarp