"Similarly, the Russian Soyuz capsule’s computer ran on only 6 kilobytes of RAM until it was replaced with newer systems in 2003, which most probably was the cause of its subsequent crash-landing in Kazakhstan."
Really? Really?
Space Shuttle computer has 1MB of RAM
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Re: Space Shuttle computer has 1MB of RAM
#12I remember my Digital Circuits prof saying the Apollo Flight Computer was constructed out of thousands of NOR-gates. At the time I was struggling to comprehend how to construct a basic circuit, so I was wow'd (and still am). http://en.wikipedia.org/wiki/Apollo_Guidance_Computer
That is'nt very surprising for a person working the semiconductor design industry. Actually there are no AND/OR/NOT gates fabricated on a modern IC.
They are all NAND gates, since they have better electrical characteristics and are Universal Gates (they can form AND/OR/NOT gates in some combination).
What is surprising is that they used NOR gates - while they are Universal Gates as well, their fabrication apparently leads to poorer electrical properties.
Re: Space Shuttle computer has 1MB of RAM
#13I remember my Digital Circuits prof saying the Apollo Flight Computer was constructed out of thousands of NOR-gates. At the time I was struggling to comprehend how to construct a basic circuit, so I was wow'd (and still am). http://en.wikipedia.org/wiki/Apollo_Guidance_Computer
The hand-woven core memory "rope" is what blew me away.
http://authors.library.caltech.edu/5456/1/hrst.mit.edu/hrs/a...
Re: Space Shuttle computer has 1MB of RAM
#14The shuttle computer does what computers do best: crunch numbers. I'd be interested in knowing what sort of hardware that RAM plugs in to, and also exactly how fast operations need to be completed in order for the shuttle to not fall out of the sky.
The shuttle uses 4 separate 1.2MHz IBM AP-101 operating in lockstep / redundant systems, with a 5th running an independent system. I assume the fifth is setup in case of software failures. http://en.wikipedia.org/wiki/IBM_AP-101 http://en.wikipedia.org/wiki/Space_Shuttle PS: It's easy to forget just how old and hacked together the Space Shuttle is: Historically, the Shuttle was not launched if its flight would run fr…
* I assume the fifth is setup in case of software failures.*
It is. The 5th has just enough to get the shuttle home, and is designed by a separate team. The presumption being that anything that knocked out the first 4 is probably a systematic failure.
Re: Space Shuttle computer has 1MB of RAM
#15For those interested in software issues in aerospace, you might want to listen to Episode 100 of Software Engineering Radio: http://www.se-radio.net/podcast/2008-06/episode-100-software...
It features an extensive interview with a guy from DLR, the German equivalent of NASA. They talk at length about culture (freedom to fail), practices (extensive re-use), and ballpark performance metrics (on the order of < 10 LOC per programmer per day).
Re: Space Shuttle computer has 1MB of RAM
#16Here is an article about developing the 'perfect' software that runs the shuttle: "They Write the Right Stuff" http://www.fastcompany.com/node/28121/print
And it's 260 engineers to write 420 KLOC. This is why software is buggy; it's to expensive to make it not buggy.
And it required 380 engineers to build the Burj Dubai.
The only difference is for most software projects it is acceptable to have "bugs" as customers will still pay for it, even if it's in a poor state of quality. But "bugs" in a 2,717 ft tower are unacceptable.
It comes down to, in general the cost of a bug in most software is relatively low compared to other engineering disciplines. Of course if the software is critical support systems for Astronauts that's a different story.
Re: Space Shuttle computer has 1MB of RAM
#17The guidance computer doesn't have enough RAM to contain the code for the entire mission, though. They have to load in a new program once the the orbiter is in space, and another one before it de-orbits.
There's a fascinating (and very detailed) series of lectures on the Shuttle's design online on MIT's OpenCourseware site: http://ocw.mit.edu/OcwWeb/Aeronautics-and-Astronautics/16-88...
Re: Space Shuttle computer has 1MB of RAM
#18I remember my Digital Circuits prof saying the Apollo Flight Computer was constructed out of thousands of NOR-gates. At the time I was struggling to comprehend how to construct a basic circuit, so I was wow'd (and still am). http://en.wikipedia.org/wiki/Apollo_Guidance_Computer
That is'nt very surprising for a person working the semiconductor design industry. Actually there are no AND/OR/NOT gates fabricated on a modern IC. They are all NAND gates, since they have better electrical characteristics and are Universal Gates (they can form AND/OR/NOT gates in some combination). What is surprising is that they used NOR gates - while they are Universal Gates as well, their fabrication apparently…
Electrical switching circuits have the possibility of two logical interpretations, fx
Electrical Positive Negative
function logic logic
L L | H 0 0 | 1 1 1 | 0
L H | H 0 1 | 1 1 0 | 0
H L | H 1 0 | 1 0 1 | 0
H H | L 1 1 | 0 0 0 | 1
NAND NORRe: Space Shuttle computer has 1MB of RAM
#19I wonder how that was all written. Is it mainly hardware, assembly or a language such as Forth?
Re: Space Shuttle computer has 1MB of RAM
#20The shuttle computer does what computers do best: crunch numbers. I'd be interested in knowing what sort of hardware that RAM plugs in to, and also exactly how fast operations need to be completed in order for the shuttle to not fall out of the sky.
The shuttle uses 4 separate 1.2MHz IBM AP-101 operating in lockstep / redundant systems, with a 5th running an independent system. I assume the fifth is setup in case of software failures. http://en.wikipedia.org/wiki/IBM_AP-101 http://en.wikipedia.org/wiki/Space_Shuttle PS: It's easy to forget just how old and hacked together the Space Shuttle is: Historically, the Shuttle was not launched if its flight would run fr…
That's weird. Why would they even need date logic in the flight software?