Does it have something to do with the way the cpu handles overflow for certain instructions? Or did I just convert an irreversiable algorithm?..remember you heard it here first!.. or are you just talking out of your butt?:)
You hit it right on.. the overflow would be bad. Anytime there is a loss of data, reversibility won't work (unless that data is saved somewhere).
but the research I'm doing/is/ with Dr. Frank. Actually, I have a meeting with him in half an hour to discuss this topic.
Intermediate state data does/not/ need to be saved. While it is important that state data is not destoyed, it is only necessary to guarentee reversiblity on the hardware level.
State data is necessary if you're performing irreversible operations.
botched the assembly... sorry:
; assume that $1 and $2 are both 0
ADDI $1 32
ADDI $2 24
ADD $1 $2
; at this point $1 should hold 56.
; and at no point have we stored anything in memory
; ok.. now let's do these instructions in reverse.
; normally, we wouldn't manually do it this way
; because the CPU would switch it, but this works
SUB $1 $2 ; ok.. $1 now contains 32
SUBI $2 24 ; now $2 contains 0
SUBI $1 32; now $1 contains 0
One problem to note with reversible computing is that your computer has to have enough memory to store every bit of information ever entered into it. I'm pretty sure that it can compress the info, but eventually you'll have to have an energy expensive and very hot 'information dumping' process. I say it's a problem, but of course normal computing requires the same thing, and doesn't let you choose when you do it.
Actually, no. It seems that way (that's what I thought at first too). But that's the cool part about it... you simply reverse the process by reversing the direction that you increment the Program Counter. I'll give a short example in pseudo assembly:
; assume that $1 and $2 are both 0
ADDI $1 32
ADDI $2 24
ADD $1 $2
; at this point $1 should hold 56.
; and at no point have we stored anything in memory
; ok.. now let's do these instructions in reverse.
; normally, we wouldn't manually do it this way
; because the CPU would switch it, but this works
SUB $1 $2 ; ok.. $1 now contains 32
SUBI $2 24 ; now $2 contains 0
SUBI $1 32; now $1 contains 0
This is a fairly primitive example, but it proves the point. The other thing is that there cannot be a MOVE instruction. Memory can be exchanged with a register value, but not copied. So, all you have to do is run the instructions backwards... I promise!!!
Well... I meant that there is a physical limit to the thermodynamics that control computers just as there is a phyical limit to the size that you can design a transistor.
In a since, we're both right. You're right, my analogy is a poor one, but it still serves its purpose.;-)
I've just joined a research group at my University to study reversible computing. The professor in charge wrote his doctoral thesis on the subject at MIT.
The concept is that a "normal" CPU erases information on every cycle (clearing registers, overwriting data, shifting data to nowhere, etc). When a CPU erases information, it's dissipated as heat. There are thermodynamic limits to this (kinda like Moore's law). So, if a computer could be designed not to erase data, you could reverse the CPU and get most of your energy back.
Now before you say "BS", think about it. In physics, if you know the initial state (starting position, velocity, acceleration) of an object in an isolated system, you can easily compute where it was at any given time earlier. This uses the same concept. For example, If you add 43 to a register, you can subtract 43 from that register and get your energy back.
Of course, certain instructions don't lend themselves to reversibility. For example, bit shifting is inherently irreversible. One option is to maintain a stack of "garbage data", but that's a poor solution. On the other hand, a number of instructions are reversible by default... XOR is always reversible, etc. So, a reversible CPU will probably have a more constrictive instruction set, but is still functional.
Reversibility is not anything new, but it does take a shift in thinking. Algorithms can be designed to run very efficiently on reversible computers, but it takes a bit more effort. Hopefully, we (the community of people studying reversible/adiabatic computers) will develop means of either converting irreversible algorithms or develop ways to make them less innefficient (double negative).
I saw a guy with a business card that said "Gentleman Extrodanaire"... while I doubt that he was a real "man whore", I imagine that it's a really great way to start a conversation with a chick...
Under "normal" conditions, a byte is 8 bits. But sending data a long distance through wires or air requires some special handling. Thus, there is a "stop" and "start" bit appended to each byte.
What about one-time passwords via S-key. The way it works is:
The system has a root password (which everybody that needs access can know). When you log in, you're presented with a phrase. On/your/ computer (not the server), you enter that phrase and your password (from above). This program generates a password that can be used ONCE!
So, no matter who's sniffing, anybody can see the exchange, but the password remains private. Do a search for "S-key" or "one time password".
Personally, I don't see what's wrong with require SSH. That/should/ be fairly safe.
I think the problem is that if you target the actual "rock", you wind up with lots of smaller fragments. Each of which is excedingly lethal. The trick is, if I'm not mistaken, to blast to the side/front to deflect it or slow it down enough that it will miss earth.
That... and do we even know what happens when you set off a nuke in space?? has that been studied/thought out?? Anybody??
I'm probably going to get flamed for this, but reading your "favorite site" almost gives me a bit of respect for Microsoft. They really have come a long way. Not to say others haven't, but...
go to any decent sized college. I'm hooked up, I know most of the other major schools around the nation are too. Kernel downloads off university mirrors ROCK...
Speaking as somebody who has been assigned community service (don't ask, it was for a traffic ticket... ), I personally doubt it. The general procedure is this:
1) you get assigned X number of community service hours (in my case 12).
2) you go to a specified governement facility where you wait in line a long fscking time
3) the boring, bored person behind the desk shows you a list of available "jobs" and you agree on one. They call the people in charge and say that you're coming in at a certain date and time.
4) you get a little form that has to be signed.
5) you work
6) they sign the form
7) lather, rinse, and repeat 5&6 until you have done X number of hours.
The problems with this are:
- open source programming can rarely (if ever) be signed off by an "authoritative" body. Sure, the project leader could say that you did X number of hours, but why would the county/state/etc trust him/her??
- open source programming isn't on their list of things that count (although THIS could be something to look into... setting up a program in your area for law-breaking programmers to work for you)
- Usually, the tasks that have to be done are for other government agencies (i.e. I washed fire engines)... perhaps non-profits count too.
- I don't think there are that many/good/ programmers that get assigned community service to make it worth-while.
- The government wants community service to suck... remember, it's a punishment (although others will argue that it's an apology). Programming is something that most programmers enjoy (duh). So making them write little bits of code really isn't going to make them not want to commit a crime again.
I just don't think it would work. Perhaps you could count it for a scholarship, they're probably a bit more flexible.
I'm not a materials engineer, but I remember seeing some demonstrations of ceramics in a class I took. They had hammers and engine componenents that were increadably strong and able to withstand extreme heat, etc. I'm not familiar with the corrosivity of ceramics, but they may hold the answer to your question. They look fairly nice too...
Just to one up you, the University of Florida is "wiring" it's campus too. And we (UF) have WAY more students than GaTech... we're currently around 45,000. So, really, this isn't a big news story.
A quarter is a denomination of US money. It is valued at US$0.25. It is a round metallic coin of measurements: 24.26mm (diameter) x 1.75mm (thickness) and weighs 5.670 g. It has a reeded (ridged) edge with 119 reeds. The front has a embossed picture of the first US president, George Washington. The back has a embossed picture of an eagle (the US symbol for freedom).
I hate to sounds like a tight wad, but there are a lot of people in this country (US) that can't spare $50. I realize that to you and I $50 isn't really a big deal, but to many people that covers to cost of food for a week (if not more). Maybe you're blind to this side of America. I know that I didn't see it for a very long time. The community where I grew up is/was a nice mid-upperclass community. Kids don't worry about how they're going to pay for college, they worry about what type of car they're parents are going to buy them when they turn 16.
It wasn't until highschool, when I went out of county to a better school, that I realized that poor people really do exist... and not in some far away city. You understand this when one friend gives another friend his old pair of worn shoes... and they both feel good about it. You understand that $50 means the difference between a good Christmas and no Christmas. You understand that $50 means the difference between eating for a week and not eating at all.
Perhaps once the poverty problems are solved then more people would be interested in things like the space program. This is a harsh thing to say, but it's reality. I grew up in Brevard County (where Kennedy Space Center is located). I understand what happens when there are budget cuts to the space program (hell, my dad works for a government contractor). But none-the-less, there are more pressing issues than space research.
yeah.. damn those bastards that own slasdot.com:Registrant:
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Ok, so let's say everything works out as planned. They pay the record companies, et. al., $1 billion over the course of 5 years. What happens after that? Who get's all the money. Does that mean that the Napster people stand to make another $1 billion over the 6-10th year for themselves after that??
Slashdot Mirror
Does it have something to do with the way the cpu handles overflow for certain instructions? Or did I just convert an irreversiable algorithm? ..remember you heard it here first!.. or are you just talking out of your butt? :)
You hit it right on.. the overflow would be bad. Anytime there is a loss of data, reversibility won't work (unless that data is saved somewhere).
Heh.. Thanks...
/is/ with Dr. Frank. Actually, I have a meeting with him in half an hour to discuss this topic.
/not/ need to be saved. While it is important that state data is not destoyed, it is only necessary to guarentee reversiblity on the hardware level.
but the research I'm doing
Intermediate state data does
State data is necessary if you're performing irreversible operations.
botched the assembly... sorry:
; assume that $1 and $2 are both 0
ADDI $1 32
ADDI $2 24
ADD $1 $2
; at this point $1 should hold 56.
; and at no point have we stored anything in memory
; ok.. now let's do these instructions in reverse.
; normally, we wouldn't manually do it this way
; because the CPU would switch it, but this works
SUB $1 $2 ; ok.. $1 now contains 32
SUBI $2 24 ; now $2 contains 0
SUBI $1 32; now $1 contains 0
One problem to note with reversible computing is that your computer has to have enough memory to store every bit of information ever entered into it. I'm pretty sure that it can compress the info, but eventually you'll have to have an energy expensive and very hot 'information dumping' process. I say it's a problem, but of course normal computing requires the same thing, and doesn't let you choose when you do it.
Actually, no. It seems that way (that's what I thought at first too). But that's the cool part about it... you simply reverse the process by reversing the direction that you increment the Program Counter. I'll give a short example in pseudo assembly:
; assume that $1 and $2 are both 0 ADDI $1 32 ADDI $2 24 ADD $1 $2 ; at this point $1 should hold 56. ; and at no point have we stored anything in memory ; ok.. now let's do these instructions in reverse. ; normally, we wouldn't manually do it this way ; because the CPU would switch it, but this works SUB $1 $2 ; ok.. $1 now contains 32 SUBI $2 24 ; now $2 contains 0 SUBI $1 32; now $1 contains 0 This is a fairly primitive example, but it proves the point. The other thing is that there cannot be a MOVE instruction. Memory can be exchanged with a register value, but not copied. So, all you have to do is run the instructions backwards... I promise!!!
Well... I meant that there is a physical limit to the thermodynamics that control computers just as there is a phyical limit to the size that you can design a transistor.
;-)
In a since, we're both right. You're right, my analogy is a poor one, but it still serves its purpose.
Thanks
I've just joined a research group at my University to study reversible computing. The professor in charge wrote his doctoral thesis on the subject at MIT.
.. XOR is always reversible, etc. So, a reversible CPU will probably have a more constrictive instruction set, but is still functional.
The concept is that a "normal" CPU erases information on every cycle (clearing registers, overwriting data, shifting data to nowhere, etc). When a CPU erases information, it's dissipated as heat. There are thermodynamic limits to this (kinda like Moore's law). So, if a computer could be designed not to erase data, you could reverse the CPU and get most of your energy back.
Now before you say "BS", think about it. In physics, if you know the initial state (starting position, velocity, acceleration) of an object in an isolated system, you can easily compute where it was at any given time earlier. This uses the same concept. For example, If you add 43 to a register, you can subtract 43 from that register and get your energy back.
Of course, certain instructions don't lend themselves to reversibility. For example, bit shifting is inherently irreversible. One option is to maintain a stack of "garbage data", but that's a poor solution. On the other hand, a number of instructions are reversible by default.
Reversibility is not anything new, but it does take a shift in thinking. Algorithms can be designed to run very efficiently on reversible computers, but it takes a bit more effort. Hopefully, we (the community of people studying reversible/adiabatic computers) will develop means of either converting irreversible algorithms or develop ways to make them less innefficient (double negative).
-Andy
key word commercial... there are many satellites that are not commercial... I'm not even going to ask their capabilities...
-andy
I saw a guy with a business card that said "Gentleman Extrodanaire"... while I doubt that he was a real "man whore", I imagine that it's a really great way to start a conversation with a chick...
Screw "programmer"... go the pimp route =)
Under "normal" conditions, a byte is 8 bits. But sending data a long distance through wires or air requires some special handling. Thus, there is a "stop" and "start" bit appended to each byte.
1 + 8 + 1 = 10.
And there you have your 10 bit byte. =)
-andy
What about one-time passwords via S-key. The way it works is:
/your/ computer (not the server), you enter that phrase and your password (from above). This program generates a password that can be used ONCE!
/should/ be fairly safe.
The system has a root password (which everybody that needs access can know). When you log in, you're presented with a phrase. On
So, no matter who's sniffing, anybody can see the exchange, but the password remains private. Do a search for "S-key" or "one time password".
Personally, I don't see what's wrong with require SSH. That
I think the problem is that if you target the actual "rock", you wind up with lots of smaller fragments. Each of which is excedingly lethal. The trick is, if I'm not mistaken, to blast to the side/front to deflect it or slow it down enough that it will miss earth.
That... and do we even know what happens when you set off a nuke in space?? has that been studied/thought out?? Anybody??
-Andy
damn... that makes almost too much sense... I might start using that idea. So you're banking regardless. =)
-Andy
What do you mean? Maybe i'm just dumb... =)
This is how I understnad you:
you work for XXX amount. If the client wants you to carry a pager, they pay (1.25)XXX ???
If you do come in after hours you charge (1 + extra overtime percentage)XXX???
Please... Enlighten me... This sounds interesting.
-Andy
I'm probably going to get flamed for this, but reading your "favorite site" almost gives me a bit of respect for Microsoft. They really have come a long way. Not to say others haven't, but...
go to any decent sized college. I'm hooked up, I know most of the other major schools around the nation are too. Kernel downloads off university mirrors ROCK...
> IE 5.5 i mean come on, ...
Doesn't this problem affect 5.0.x also?? I though I remember hearing that.
-Andy
Speaking as somebody who has been assigned community service (don't ask, it was for a traffic ticket... ), I personally doubt it. The general procedure is this:
/good/ programmers that get assigned community service to make it worth-while.
1) you get assigned X number of community service hours (in my case 12).
2) you go to a specified governement facility where you wait in line a long fscking time
3) the boring, bored person behind the desk shows you a list of available "jobs" and you agree on one. They call the people in charge and say that you're coming in at a certain date and time.
4) you get a little form that has to be signed.
5) you work
6) they sign the form
7) lather, rinse, and repeat 5&6 until you have done X number of hours.
The problems with this are:
- open source programming can rarely (if ever) be signed off by an "authoritative" body. Sure, the project leader could say that you did X number of hours, but why would the county/state/etc trust him/her??
- open source programming isn't on their list of things that count (although THIS could be something to look into... setting up a program in your area for law-breaking programmers to work for you)
- Usually, the tasks that have to be done are for other government agencies (i.e. I washed fire engines)... perhaps non-profits count too.
- I don't think there are that many
- The government wants community service to suck... remember, it's a punishment (although others will argue that it's an apology). Programming is something that most programmers enjoy (duh). So making them write little bits of code really isn't going to make them not want to commit a crime again.
I just don't think it would work. Perhaps you could count it for a scholarship, they're probably a bit more flexible.
Interesting idea though...
I'm not a materials engineer, but I remember seeing some demonstrations of ceramics in a class I took. They had hammers and engine componenents that were increadably strong and able to withstand extreme heat, etc. I'm not familiar with the corrosivity of ceramics, but they may hold the answer to your question. They look fairly nice too...
-Andy
Just to one up you, the University of Florida is "wiring" it's campus too. And we (UF) have WAY more students than GaTech... we're currently around 45,000. So, really, this isn't a big news story.
-Andy
A quarter is a denomination of US money. It is valued at US$0.25. It is a round metallic coin of measurements: 24.26mm (diameter) x 1.75mm (thickness) and weighs 5.670 g. It has a reeded (ridged) edge with 119 reeds. The front has a embossed picture of the first US president, George Washington. The back has a embossed picture of an eagle (the US symbol for freedom).
t ion=coin_specifications.
Info on other US coins can be found here: http://www.usmint.gov/about_the_mint/index.cfm?ac
I hate to sounds like a tight wad, but there are a lot of people in this country (US) that can't spare $50. I realize that to you and I $50 isn't really a big deal, but to many people that covers to cost of food for a week (if not more). Maybe you're blind to this side of America. I know that I didn't see it for a very long time. The community where I grew up is/was a nice mid-upperclass community. Kids don't worry about how they're going to pay for college, they worry about what type of car they're parents are going to buy them when they turn 16.
It wasn't until highschool, when I went out of county to a better school, that I realized that poor people really do exist... and not in some far away city. You understand this when one friend gives another friend his old pair of worn shoes... and they both feel good about it. You understand that $50 means the difference between a good Christmas and no Christmas. You understand that $50 means the difference between eating for a week and not eating at all.
Perhaps once the poverty problems are solved then more people would be interested in things like the space program. This is a harsh thing to say, but it's reality. I grew up in Brevard County (where Kennedy Space Center is located). I understand what happens when there are budget cuts to the space program (hell, my dad works for a government contractor). But none-the-less, there are more pressing issues than space research.
-Andy
yeah.. damn those bastards that own slasdot.com:Registrant:
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Aston, MA 01720
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Domain Name: SLASHDOT.COM
Administrative Contact, Technical Contact:
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Andover.Net
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Billing Contact:
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Andover.Net
50 Nagog Park
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Record last updated on 11-Apr-2000.
Record expires on 11-Apr-2001.
Record created on 11-Apr-2000.
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Domain servers in listed order:
NS1.ANDOVER.NET 209.207.224.196
NS2.ANDOVER.NET 209.207.224.197
Slashdot.net on the other hand... that's somebody else's doing.
-Andy
that URL seems to be a little defunct (perhaps they moved some files) try this one
Ok, so let's say everything works out as planned. They pay the record companies, et. al., $1 billion over the course of 5 years. What happens after that? Who get's all the money. Does that mean that the Napster people stand to make another $1 billion over the 6-10th year for themselves after that??
yeah, but they'll throw in a house and a car for free... =)
;-)