6 Dec
2014
6 Dec
'14
6:55 p.m.
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)...
(Although occasionally, back when, one used to see things that were 1.5 times
a power of two, e.g. on a 16-bit machine, 12KB, 96KB, etc - physical and cost
constraints tended to produce those. I don't recall the last time I saw
something that wasn't a power of two - probably those 96KB jobs.)
With disk drives, on the other hand, one can get all sorts of arbitrary sizes,
produced by the number of cylinders, numbers of heads, etc, etc.
Noel
6 Dec
6 Dec
7:13 p.m.
Several early IBM computers used decimal addressing; the IBM 1401 at the
Computer History Museum in Mountain View CA is an example. I think is has
16,000 locations. If BCD addressing had won out there would not be a
problem with disk vs RAM capacity.
Michael
-----Original Message-----
From: cctalk [mailto:cctalk-bounces at classiccmp.org] On Behalf Of Noel
Chiappa
Sent: Saturday, December 06, 2014 6:55 PM
To: cctalk at classiccmp.org
Cc: jnc at mercury.lcs.mit.edu
Subject: Re: Weekly Classic Computer Trivia Question (20141205)
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)...
(Although occasionally, back when, one used to see things that were 1.5
times a power of two, e.g. on a 16-bit machine, 12KB, 96KB, etc - physical
and cost constraints tended to produce those. I don't recall the last time I
saw something that wasn't a power of two - probably those 96KB jobs.)
With disk drives, on the other hand, one can get all sorts of arbitrary
sizes, produced by the number of cylinders, numbers of heads, etc, etc.
Noel
8:20 p.m.
On 12/06/2014 06:55 PM, Noel Chiappa wrote:
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.
The numbers sound bigger.
--Chuck
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)... 
7 Dec
7 Dec
9:10 a.m.
On 12/06/2014 10:20 PM, Chuck Guzis wrote:
On 12/06/2014 06:55 PM, Noel Chiappa wrote:
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?
Jon
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)... 
8 Dec
8 Dec
11:54 a.m.
From: Jon Elson
Sent: Sunday, December 07, 2014 9:11 AM
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?
As it happens, I saw this discussed somewhere else in the last few
months by someone who actually worked on these things (probably on
alt.folklore.computers, come to think of it).
They left holes in memory while running 1401 emulation.
Rich
Rich Alderson
Vintage Computing Sr. Systems Engineer
Living Computer Museum
2245 1st Avenue S
Seattle, WA 98134
mailto:RichA at LivingComputerMuseum.org
http://www.LivingComputerMuseum.org/
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