Re: CISC (ugh!) question

[DrFranken <midrange@xxxxxxxxxxxx>]

There were three memory card slots in the B50 as I recall. Each 
supported a 16MB Memory card.  You may recall the memory cards of the 
day were somewhere around 9 inches by 12 inches or so and memory was 
very pricey. Next 'logical' memory size would have been 32MB cards and 
likely for the B50's 9.3 CPW (No, not even double digits) wouldn't have 
been worth the investment.

Actually the very first 'Franken' I did was when we swapped our IBM 
memory on our B45 for some other brand (I've forgotten which.)  The B45 
supported one 8MB and two 16MB Boards for 40MB Total. When the 
replacement memory came it had switches on it for 'Slot 1' and 'Other'.  
The boards we all identical. I surmised, as it turns out correctly, was 
the switch changed the board from 8 to 16MB.  Anyone want to hazard a 
guess as to what I did next? :-)  Of course, I flipped the switch on 
board one and IPLed. Shazaam we had 48MB on the B45.

Could very well be it was a marketing limitation for the B45 or there 
could have been issues IBM identified that we simply didn't run into and 
'got lucky'.

Some may remember the S/36 model "D" had a 7 MB limit and the same trick 
worked on that thing - swap in a 2MB board in slot 1 to get up to 8MB 
memory.

Many of you remember the 170 that had a limit of 832MB (6x128 + 2x32MB). 
The thing perfectly supported 1GB if you pulled the 32's and replaced 
with 128's. An IBMer told me they simply didn't want to put in the order 
process to replace those 'base memory' 32's with 128s as that much 
additional memory wasn't likely to help enough to be worth it on a 
system that small.

 - Larry "DrFranken" Bolhuis

On 9/29/2011 5:27 PM, John McKee wrote:
>   A few weeks ago, I saw something on the list about how a modern system (can't recall if the system referred to was a 270 or whatever).  Just remember that "the doctor" described the possible memory expansion for it.  And that expansion was not "official" from IBM as I recall.
>
> Which brought this nagging question to mind.  There is no practical value to any answer - except pure unrelenting curiosity.  I worked with a B50.  It was purchased with 24M of RAM.  Prior to my arrival, a deal was made to swap the genuine IBM memory for 48M of IPL memory.  That system was loaded down beyond belief.
>
> I was told that 48M was the absolute maximum memory that the B50 could address.
>
> This was obviously way before any customer oriented maintenance on a RISC system.
>
> Was 48M the absolute maximum memory that the old beast could support?
>
> My assumption, based on tremendous change in nearly 20 years is that 48M was indeed the maximum.  But, why 48?  Not a power of 2.
>
>
> John McKee