Author: Uri Blass
Date: 16:16:17 03/27/01
Go up one level in this thread
On March 27, 2001 at 19:00:12, Andrew Dados wrote: >On March 27, 2001 at 18:12:42, Christophe Theron wrote: > >>On March 27, 2001 at 14:08:03, Robert Hyatt wrote: >> >>>On March 27, 2001 at 12:55:10, Christophe Theron wrote: >>> >>>> >>>> >>>>That's right. >>>> >>>>Actually as the title says, the message is directed to people who are >>>>considering to buy a dual. >>>> >>>>As far as I know quads are so expensive that it would be ridiculous to buy one >>>>just to play chess. >>>> >>>> >>>> >>> >>> >>> >>>At the moment, perhaps. 6 years ago duals were just as expensive. Now they >>>are dirt cheap. As quads become more common, their prices will continue to >>>drop. 5 years ago a quad MB for pentium pro 200s would set you back almost >>>$8,000. Today you can buy an Intel SC450NX for 2500 bucks, that includes >>>three hot-swappable 400 wat power supplies, motherboard, 6-slot hot-swap raid >>>disk cage, 3 on-board scsi controllers, 1 on-board video controller, etc. >>> >>>All you lack is cpus, memory and drives. >>> >>>That is a huge reduction. The curve is going downward each year. Now the >>>quads are slowly reaching reasonable price points while the 8-way boxes are >>>way expensive. In 5 years that too will change I'll bet... >> >> >> >>So I would advice people who are considering buying a dual right now to delay >>their buy by several years... >> >> >> >> >> >>>>You are always thinking with unlimited resources in mind! >>>> >>>>I don't disagree with you here, but in real life there are people wondering if >>>>it's worth it to buy a dual. >>>> >>>>And depending on how much money they can put on it, they will have to choose >>>>between a single 1.GHz and a dual 1GHz. >>> >>>OK... but there the dual will perform like a 1.7ghz machine. Which will >>>turn into around 60 rating points improvement. That is not trivially >>>ignorable. >>> >>>Each time I teach a parallel programming course here, I will find around one >>>out of every 10 students has a dual-processor machine already. And when I ask >>>what they paid, they generally say 500-1000 US bucks... >> >> >> >>In the place I live, I cannot even buy a dual. I must order it overseas. >> >>Bob, there are people outside the United State of America, you know. >> >>You are very lucky to live in a place where you can get all kind of high tech >>stuffs for a fraction of your monthly salary, but in other countries a dual >>represents a huge amount of money. >> >>For example, a dual represents more than my average monthly salary. >> >> >> >> >> >>>>If you can afford to buy a dual 1.2GHz, then you just stop after reading the >>>>first paragraph. >>>> >>>>If not, then I think the rest is worth reading... >>>> >>>> >>>> >>>> >>>>>That is flawed. For multiple reasons. The shared hash table holds _most_ EGTB >>>>>results after a single probe. The EGTB cache is threaded and shares data read >>>>>between the two (or more threads). With the compression scheme Eugene uses, >>>>>the reads are kept to a minimum. I have run extensive tests on my quad with >>>>>one single 9-gig SCSI drive servicing 4 threads for EGTB reads. I don't see >>>>>any severe strangulation due to disk backlogs. most threads are searching >>>>>close enough to each other in the tree that they are probing the _same_ >>>>>tablebases. The caching Eugene wrote handles this quite well. >>>> >>>> >>>> >>>>OK, I admit that I have not done any test on this issue, so your input is >>>>appreciated. >>>> >>>>If my figures are wrong I will publish an update for this text. >>>> >>>>Do you have any measure of the slowdown expected when 2 thread are accesing >>>>intensively the same EGTB files? That would help us to compute the corresponding >>>>ELO loss. >>> >>>I generally don't notice any degradation at all. Mainly because of the large >>>well-managed cache buffers, no doubt. But then the operating system also does >>>a lot of file caching on top of what Eugene does, and all of this (on a 512mb >>>machine) goes a long way toward controlling "disk buzz". >> >> >> >>Well on my computer when I set up an endgame position I have my hard disk >>working really hard. >> >>I can hardly see how this poor hard disk could manage to serve two threads >>instead of one without some performance penalty. >> >>On the other hand, if you need to have a high perf SCSI drive to satisfy the >>needs of the dual, and such an amount of memory, this has to be added to the >>invoice. >> >>Remember that all this is about what you get for the money, what you need really >>and is it worth it. >> >> >> >> >> >>>>I did not try to cover quads in the message because I don't think many people >>>>could afford to buy one. >>>> >>> >>>I realize that. But 5 years ago you wouldn't have found anyond considering >>>buying a dual either. Quads will eventually reach the same pricing level, >>>based on a curve over the last 5 years.. >> >> >> >>People, wait for 5 years before you buy a SMP machine. >> >> >> >> >> >>>>So far I have seen a number of people on CCC asking for duals, but nobody ever >>>>said he was considering to buy a quad. >>>> >>>> >>>> >>>> >>>> >>>>>>A difference in ELO points in real life turns into a winning percentage. >>>>>>That's exactly what ELO means, and how it is computed. >>>>>> >>>>>>For winning percentages above 20% and under 80%, there is an approximated >>>>>>formula that works pretty well: >>>>>> >>>>>> ELOdiff = ( WinPercentage - 50 ) * 7 >>>>>> >>>>>>From this you can deduce how to compute WinPercentage if you have the ELOdiff: >>>>>> >>>>>> WinPercentage = ELOdiff / 7 + 50 >>>>>> >>>>>>If ELOdiff=25, then WinPercentage = 53.57% (we are between 20% and 80% >>>>>>so our above formula applies). >>>>>> >>>>>>So we are talking about a difference of 3.5 games each time you play 100. >>>>>> >>>>>> >>>>>>**************************************************************************** >>>>>>** When you play 100 games with your dual 1GHz against ** >>>>>>** your single 1.2GHz, you can expect the dual to win typically ** >>>>>>** by a 3.5 games margin. ** >>>>>>**************************************************************************** >>>>> >>>>> >>>>>I would change that to >>>>> >>>>>winpct=60/7+50 which is about 60%. Out of 100 games that turns into winning >>>>>60 and losing 40. BTW in your above comment you need to double that 3.5. If >>>>>I win 53.5 games out of 100, you win 46.5. The _difference_ is 7 games. Not >>>>>3.5 >>>> >>>> >>>>When you win a game, your opponent loses it. I don't count this as 2 games. >>>> >>>> >>>> >>>> >>> >>>Then maybe your term wasn't clear to me instead. You said "I win 53.5% of >>>the games. Out of 100 games that is a difference of 3.5 games." If I win >>>53.5% of the games, you win 46.5% of the games. That is a bit different >>>since our scores are separated by 7, not 3.5... >> >> >> >>OK, OK. I don't want to split hairs. >> >>What counts is the difference between the winning percentage and 50%. Because it >>is what you multiply by 7 to get an estimate of the ELO difference. >> >>If I run a match with even hardware, I win 50 out of 100 games. >> >>If I run a match with a dual I win 53.5 out of 100 games. >> >>With my dual I win 3.5 more games. OK? > >NO, you win 7 games more then before :) > >before: 100 draws; >now: 93 draws and 7 wins... > >-Andrew- It is not clear. It also may be: Before 35 wins and 30 draws. After 35 wins and 37 draws. In this case you win 0 games more than before and the 3.5 difference is only because you lose less than before. Uri
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