Čet, 20.11.2008.

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Athlon 64 4800+ X2 - dvoglavi zmaj u akciji
22.06.2005.
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- Uvod - nastavak -

AMD-ov pristup kombiniranje para jegzri sa jednim memorijskim kontrolerom u istom pakiranju ima svoje prednosti i mane. Prednost je mogućnost lakše sinkronizacije cachea. Budući da obje jezgre manipuliraju podacima iz radne memorije računala, SMP (Simultaneous Multi-Processing) sistemi koriste posebne protokole za održavanje koherencije cachea. Dok Intel koristi protokol MESI (Modified-Exclusive-Shared-Invalid), AMD rabi efikasniji protokol pod imenom MOESI (Modified-Owner-Exclusive-Shared-Invalid).

"CD" na kraju oznake procesora označava dvije jezgre

Svaki od termina od kojih je sačinjeno ime protokola označava tip statusa podatka u radnoj memoriji SMP računala. Exclusive znači da se podatak nalazi u cacheu jedne od jezgri, Shared znači da obje jezgre imaju jednak podatak u cacheu, Modified znači da je jedna od jezgri djeljeni podatak modificirala (ako je podatak do tad imao status Shared) dok u tom slučaju isti podatak za drugu jezgru dobija status Invalid. U slučaju ovakve "tuče" oko istog podatka, Intelovi SMP sustavi (bilo da je riječ o dvojezgrenim procesorima ili dvoprocesorskim računalima) moraju čekati da se podaci iz cachea jedne od jezgri (one koja je prva modificirala podatak) vrate u radnu memoriju. Tek onda ih druga jezgra smije kopirati u svoj cache i ponovo ih modificirati. Naravno, problem je u tome što Intelovi procesori u SMP računalima odnosno jezgre u dvojezgrenim procesorima međusobno komuniciraju preko čipseta.

Pogled iznutra

AMD ovu zbrku elegantno zaobilazi preko logike za nadzor zahtjeva procesora - System Request Queuea. U protokolu MOESI zato postoji još jedna oznaka, Owner, koja označava da je podatak koje dijele obje jezgre jedna od jezgi modificirala. Da bi druga jezgra pristupila modificiranom podatku, podatak nije potrebno vraćati u radnu memoriju već se on kopira u cache druge jezgre interno, preko SRQ-a.

Mana korištenja dvije jezgre sa jednim memorijskim kontrolerom je manjak fleksibilnosti pri proizvodnji. Intel svoje dvojezgrene procesore može razrezati napola i od svake jezgre napraviti jedan procesor. Drugim riječima, Intel za proizvodnju dvojezgrenih procesora rabi jednake wafere kao i za proizvodnju monojezgrenih procesora. AMD nema ovaj luksuz već monojezgrene i dvojezgrene procesore mora proizvoditi na zasebnim waferima.



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Moj idući procesor će biti:
Intel Core i7
Ne kupujem novi, dobar je i ovaj koji imam
Neki drugi
AMD Phenom II X4


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