Author: Robert Hyatt
Date: 11:08:03 03/27/01
Go up one level in this thread
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... > > > >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... > >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". > > >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.. >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...
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