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Various 1401 Models

- Who to blame ;-))
- Jˇhann Gunnarsson adds
- Jeff Kellem adds more
- Model A Power Supplies
- Graphs of Rental Prices
- Results - to be determined ;-))

Who to blame ;-))
I prefer to "blame" Ken Shirriff for triggering this web page ;-))

Subject: 1401_software] What are the different 1401 models?
From: Ken Shirriff < >	 	 
Date:	Fri, Feb 06, 2015 8:56 pm
To:	1401 Software Team <>

I was wondering about the different 1401 models and maybe someone here knows the details.

After reading various documents on the website, I've been able to figure out:

Model A: the single-cabinet model that doesn't support expansion
Model B: the card-reading model
Model C: the card and tape model. Is this what the Computer History Museum has?
Model D: the tape-only model. Since there's no card reader, 
           the power supply is moved into the 1401
Model E: a mystery to me
Model F: the disk model
Model G: advertised as compatible with the larger 1401s, 
          but I don't know in what way it is smaller.

Anyone know more about the different models, especially the mysterious E and G? 
How is the internal layout of the different models changed? 
Where do the power supplies go in the A and D?


Jˇhann Gunnarsson < > IcelandNumbers.html, Movies-n-Sounds.html#Johann came back with
Hi everyone,

There is a brochure describing the 1401 model G on the 1401 info website:

It was an entry system with reduced card reading and printing speed, possibly also reduced clock speed, although not mentioned in the brochure.

I happen to have a copy of IBM 1401 General Information Manual published in 1959. On page 11 there is a table describing the various models of the initial announcement. I enclose a scan of page 11.

I do not know model E, nor do I remember where the power supplies were in Model A.

Hope this helps.

Jˇhann Gunnarsson

from: Jeff Kellem < >
To: Jˇhann Gunnarsson
CC: - lots of folks -

There are also mentions of some of the 1401 models in one or two of the other brochures on the page that Jˇhann sent. (Hi, Jˇhann.) At least in:

IBM 1401 Data Processing Systems
The IBM 1401 Model G Card Data Processing System
The IBM 1401 G

on that brochures page:

I'm currently borrowing some Service for Consultants guides from 1976, mostly for my research on the IBM 1403 printer and its typefaces. I've attached a PDF of a few pages from that. It shows the model E as a tape and card model (similar to the relationship between the B and C). Here's a simplified version of the chart:

Model G: Basic Card Systems
Model A: Card Systems.
Model B: Expanded Card Systems.
Model C: 729 Tape Systems.
Model D: 729 Tape/Card Systems.
Model D1: 7330 Tape/Card Systems.
Model E: 7330 Tape Systems.
Model F: 1405 Disk/Card Systems.
Model F1: 1405/729 Disk/Tape/Card Systems.
Model F2: 1405/7330 Disk/Tape/Card Systems.
You can also see the pricing in 1976 in these charts. as .pdf file,
724 K bytes

According to Earl Bloom in a comment in the IEEE Spectrum piece on the CHM restoration: "co-designer of the 1401 Model G which interleaved processing with card reading, punching and printing which significantly improved overall performance!"

The power for the 1401 Model A comes from the 1402 unit, according to some of the manuals referenced below.

There are also some physical descriptions of the 1401 (models A through F) in the IBM 1401 Installation Manual -- Physical Planning:

from the 1401 Hardware System section of the 1401 info website:
Some limited information can also be found in the IBM 1401 System Summary manual linked in that same section.

A few details can be teased from the IBM 1401 OEM Information manual, though I believe it only mentions model A through F:

and the Field Maintenance Manual from the 1401 Processor section :

Hope that helps a little in your research.


Model A Power Supplies
from Jud McCarthy -

... but the power supplies for the single cube Model A were in gates A4 & A5. ------

Graphs of Rental Prices - from Ken Shirriff - Feb 15, 2015
I made a graph of the 1976 rental prices in Jeff's attachment. The pricing scheme is interesting, but a bit puzzling. Basically, the price is determined by the memory and tape drive type; other things don't really matter.

The top price tier is for 729 systems: C with card, D without card, and F with disk and card. The next price tier is 7330 systems: D, F with disk and card, and E with card. The next tier is systems with no tape: F with disk and card, B with card, and A with card. At the bottom are the slower G systems with card.

It's a bit strange that having disk support doesn't cost anything extra, but the different tape support costs much more. Is the interface for the 7330 less complicated? I assume these prices are for just the 1401 and don't include the tape drives.

The memory pricing is also interesting. Going from 1.4K to 2K costs about $105, 2K to 4K costs $135, 4K to 8K costs $50, 8K to 12K costs 20, and 12K to 16K is free.

It's hard to make sense of the memory pricing. The small memory increments are much, much more expensive than the large ones. Maybe these prices don't include the 1406 memory unit, but then I don't know why you would need to pay more for 12K than 8K.

Another interesting thing is the $333/month charge for multiply/divide or $11,950 purchase. Overlap is $255/month or $15,380 purchase - so overlap is much cheaper than multiply to rent, but much more to purchase. In general, the rental prices are 1.5% to 3% of the purchase price, but there's a lot of variation.

I don't know anything about pricing beyond this data, so I'd be interested in comments from people who know the real story. Ken

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