Talk:ILLIAC IV

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Cray I faster or slower than ILLIAC IV?[edit]

The article on Cray Inc. states that "The Cray-1 was a major success when it was released, faster than all computers at the time except for the ILLIAC IV." But this article on ILLIAC IV states that "(ILLIAC IV) was finally ready for operation in 1976, after a decade of development that was now massively late, massively over budget, and outperformed by existing commercial machines like the Cray-1." These two articles seem to contradict each other. —The preceding unsigned comment was added by 71.50.113.68 (talkcontribs) 21:18, 25 April 2006 (UTC)

Not only that, but the ILLIAC article contradicts itself. It says at the top of the page that the Cray-1 was faster, but says at the bottom of the page that the Illiac began operation in 1976, the same year the Cray-1 was released with roughly the same performance. --Blainster 08:25, 26 April 2006 (UTC)


I never had a chance to use the ILLIAC IV, but I know many people who did and had an office in the building which housed it (at the moment I am across the street). So the issue boils down to what many people call an "apples-to-apples" comparison. If you are an armchair supercomputer watcher as most are, you only look at clock speed. If that were true then any latter (more recent) machine will generaly be faster. I never directly used a Cray-1 or a Cray-1S either, but I did use the X-MP/2 (upgraded to an X-MP/4) which succeeded the 1S which replaced the IV.

The ILLIAC had a slower individual processor element (PE) or control unit (CU) than the Cray-1. The serious computational philosophy question is whether one can add parallel work in sum. Software engineers like Fred Brooks say no. Managers of budgets today have to say yes (is 64 slower elements comparable to a machine 64 times faster than an individual element? No simple answer).

Additionally, speed ignores memory: both RAM and disk in this case. The ILLIAC had woefully little memory. It was only usable with the fixed head disks holding the main part of the problem and the processing unit memories acting as cache and the programmer acting as memory manager. Serious (real, not toy) supercomputing problems take up all memory (only toy problems sat in processor memory).

To this day the ILLIAC was faster in I/O, with at best a weak comparison to Connection Machine Data Vaults (non fixed head disks, much slower), than any other machine since. Apparently the much touted optical memory as tertiary store never worked. I have seen some of the optical strips (it was not disk).

--enm 1 jun 2006

"destined to be the last" really need to be edited out, as even the page for ILLIAC notes the ILLIAC 6.

--enm 1 jun 2006

I'm not sure I see the point in your comment? I assure you as the primary author of the article, I certainly don't compare machines based on clock speed. I thought the article was fairly fair on this. If the article reads this way, and it doesn't seem to, please edit away! Maury 04:24, 28 November 2006 (UTC)
No, I am not the author of the article. Every one but the knowledgeable have contributed to this article (seriously). It appears mostly a rehash of the literature and second hand knowledge that people read or heard. Comparison is done on the basis of real codes and balanced systems. People remember CPUs and their clock cycles, they rarely remember the other parts of systems like storage. Too much in this article needs a rewrite for an old system which I never used which I don't have time for.... --enm 143.232.210.150 (talk) 16:07, 16 September 2008 (UTC)

This last comment is correct. When I recently discovered this page I found that it was almost entirely based on what can only be called rumor or a complete fiction, not even second hand information. Not only was the history wrong, but so was the computer science. As a member of the Illiac IV group at Illinois, worked on the machine in Paoli and was involved in the campus demonstrations (my office was fire-bombed, luckily it didn't go off), I have now updated it (and I conferred with other members of the project in doing it). More of course could be said, but what is there now is accurate. Jeanjour (talk) 15:04, 21 December 2012 (UTC) John Day

1 Tbit optical storage device?[edit]

I flagged the mention of a 1 Tbit optical storage device as "citation needed". That's roughly 3 orders of magnitude more storage than state of the art magnetic disk drives in 1976, i.e., it's hard to believe that the claimed capacity is anywhere near accurate. Paul Koning (talk) 18:29, 14 October 2013 (UTC)

I have added a reference to the description of the "laser memory", the paper can be found at a New Zealand university website (unable to include the URL due to some blockage). Quoting the paper, it has the following description:

1) Laser memory: The B6500 supervises a 10^12-bit write-once read-only
laser memory developed by the Precision Instrument Company. The beam
from an argon laser records binary data by burning microscopic holes
in a thin film of metal coated on a strip of polyester sheet, which is
carried by a rotating drum. Each data strip can store some 2.9 billion
bits. A "strip file" provides storage for 400 data strips containing
more than a trillion bits. The time to locate data stored on any one
of the 400 strips is 5 s. Within the same strip data can be located in
200 ms. The read and record rate is four million bits per second on
each of two channels. A projected use of this memory will allow the
user to "dump" large quantities of programs and data into this storage
medium for leisurely review at a later time; hard copy output can
optionally be made from files within the laser memory.

--Nigwil (talk) 09:29, 20 October 2013 (UTC)

What was the contribution of the Illiac IV?[edit]

This video The Illiac-IV lecture - Bay Area Computer History Perspectives Series provides a long list of the problems that the Illiac IV solved and how the results were still used beyond the life of the machine. — Preceding unsigned comment added by Nigwil (talkcontribs) 09:25, 20 October 2013 (UTC)