For some processor models -- I forget whether S/360 or later -- add-on memory vendors would install more memory than IBM designed for, expanding memory address/data buses to allow it. And of course when such processors returned to IBM they had to be de-extended, returned to IBM's limited address range. It must have been fun selling maintaining competitive memory.
Quoting: All the focus on early memory prices also glosses over the fact that when the S/360 was introduced in 1964 even the largest models had a physical memory limit of 8 MiB, and the S/360 architectural limit was only 16 MiB. If you used a memory-extravagant design and created an application requiring memory beyond available limits, the cost of memory became effectively infinite - not available at any price. Larger record sizes impacted requirements for not only main memory but external storage capacity and channel bandwidth and processing time to manipulate the data. There definitely was a mindset in place in earlier days that placed great value on conserving all hardware resources as much as possible, to the point of obsession in some cases. If you exceeded available resources then, the hardware upgrade cost was more likely to be cost-prohibitive, or the upgrade might not even be possible. ---------------------------------------------------------------------- For IBM-MAIN subscribe / signoff / archive access instructions, send email to lists...@listserv.ua.edu with the message: INFO IBM-MAIN
