Weekly Classic Computer Trivia Question (20141205)

Jon Elson elson at pico-systems.com
Sun Dec 7 11:10:59 CST 2014

On 12/06/2014 10:20 PM, Chuck Guzis wrote:
> On 12/06/2014 06:55 PM, Noel Chiappa wrote:
>>      > From: Jerome H. Fine
>>      > I would point out that one reason that memory may 
>> have stayed with 2 **
>>      > 30 is that memory is usually produced and sold in 
>> multiples of 2 ** 30
>>      > these days
>> Main memory has pretty much _always_ been sold in blocks 
>> that were exact
>> powers of two, for obvious reasons (at least, powers of 
>> two of the word size
>> of the machine in question)...
> Let's see; IBM 1620--basic memory size=20,000 digits, 
> increments of 20,000 digits up to 60,000.  IBM 705, 7080,...
> What is curious is the marketing numbers used for the 
> memory size.  65K, 131K, etc.  I believe IBM was guilty of 
> this in their S/360 marketing literature.
Say, this brings up a question I've always wondered about.  
On the emulation
microcode for the 360 series that ran decimal machine code, 
such as
the 1401, did they translate every address from decimal to 
binary before
accessing the memory, or did they just use the bare BCD 
address, leaving
little and big holes all over the binary address space?  
Obviously, the
translation to binary would take up a lot of time, and on 
machines with
enough memory it didn't make so much difference.  But, the 
holes all over
would play hob with channels accessing the memory.  But, at 
least the 1401
series apparently had I/O buffers at fixed memory addresses, 
so maybe
that wasn't such a big deal.

Anybody know?


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