> IBM 701 with 2048, later 4095 36 bit word

ITYM 4096

The Williams Tube was one of those technologies that I was too young to know 
about, for which I am grateful.

> two digit dates and Packed Decimal 

It's not that hard to used unsigned packed decimal for a three digit year in 
two bytes.


--
Shmuel (Seymour J.) Metz
http://mason.gmu.edu/~smetz3

________________________________________
From: IBM Mainframe Discussion List <IBM-MAIN@LISTSERV.UA.EDU> on behalf of 
Nightwatch RenBand <johnmattson...@gmail.com>
Sent: Thursday, August 15, 2019 11:33 AM
To: IBM-MAIN@LISTSERV.UA.EDU
Subject: Reason for 2 digit years was Re: Instruction speeds

My first programming experience was in the mid to late 1960's and even then
there were "old timers" who explained things like this in lurid detail;
perhaps, as King Henry V said " with advantages what feats he did that
day". As I remember they said that the problem was memory.  They programmed
on IBM 701 with 2048, later 4095 36 bit wordd of CRT memory.  Yes, you
could output to tape or punched cards, but you had to do your calculations
in main memory.  Virtual memory had been proven in the labs, but for years
programmers struggled with "overlays" where your code actually moved the
next routine into memory before continuing processing.  Naturally, the
smaller you could make your code and data areas the less you would have to
do overlays, so two digit dates and Packed Decimal saved main memory at the
cost of cpu cycles.  Also the reason that the ZAP and AP commands were
devised.  CPU cycles are a cost, but remember that overlays take many more
instructions than packing dates, and programmer time was just as expensive,
perhaps more so, than today (since wages have been close to stagnant since
about 1980).  Oh, did I mention that they were programming with early
Assembler which did not include symbolics?  You had to remember the offsets
for every piece of data as well as the location of the instructions in
memory.  Perhaps that's why so many of them smoked and drank.
    SO that's the story as they saw it.  It may not stand up to rigorous
computer science analysis, but it "seemed like a good idea at the time".
Which reminds me of my favorite joke.  From the Maginficent Seven"
https://www.youtube.com/watch?v=0ieicflBG_Y

Calvera: What I don't understand is why a man like you took the job in the
first place, hum? Why, heh?

Chris: I wonder myself.

Calvera: No, come on, tell me why.

Vin: It's like this fellow I knew in El Paso. One day, he just took all his
clothes off and jumped in a mess of cactus. I asked him that same question,
"Why?"

Calvera: And?

Vin: He said, "It seemed like a good idea at the time."

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