[QUOTE="nyzma23"]
[QUOTE="rocoswav"]
http://www.amd.com/us/products/technologies/gddr5/Pages/gddr5.aspx
ronvalencia
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it's GPU MEMORY not SYSTEM MEMORY ,gddr5 only good when used for gpu memory because of high bandwidth but worse when used for system memory because of high latency that's where ddr3 shine
there's a reason why pc have 2 different type of memory ddr3 for system and gddr5 for gpu
GDDR5's latency example https://www.skhynix.com/products/graphics/view.jsp?info.ramKind=26&info.serialNo=H5GQ2H24AFR
Programmable CAS latency: 5 to 20 tCK
Programmable WRITE latency: 1 to 7 tCK
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DDR3's latency example http://download.micron.com/pdf/datasheets/dram/ddr3/1Gb_DDR3_SDRAM.pdf
CAS READ latency (CL): 5, 6, 7, 8, 9, 10, or 11
CAS WRITE latency (CWL): 5, 6, 7, 8, based on tCK
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http://forums.anandtech.com/showpost.php?p=34710477&postcount=28
Memory latency is most appropriately measured in nanoseconds. In terms of nanosecond latency, DDR3 and GDDR5 are very similar. Someone already posted a link that says that GDDR5 has programmable CAS latency (from 5 to 20 cycles), which if you take the increased clockspeed of GDDR5 into account, means that the latency in terms of nanoseconds is very similar to DDR3.
GDDR5's architecture is different from typical DDR3 in only a few important performance-oriented ways: * More banks (16 in GDDR5 versus 8 [typical] in DDR3, this is actually a latency-*reducing* feature). * More data pins per GDDR5 device (32 in GDDR5 versus [typicall] 8 or [very rarely] 16 in DDR3). This makes it so you can get all of the data for a cache line (or whatever granularity of access you're talking about), in a reasonable number of cycles from a single chip. In DDR3, all 8 chips in a rank work together to provide 64 bits per transfer of a cache line (8 bits per transfer each). This width, plus the very high clockspeed of GDDR5 has the net effect of data transfer taking *less time* with GDDR5 compared to DDR3, but data transfer is never the latency bottleneck in a DRAM system, so this part isn't very important. Suffice it to say, this does not have any negative impact on GDDR5 latency. * Obviously also very high clockspeeds and data transfer speeds.
As a source, other than the link provided earlier in the page, I myself researched DRAM for a couple years, and my lab mate just finished the GDDR5 version of his DRAM simulator, with all the industry-correct timing parameters involved, and according to him they have the almost identical latency.
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http://www.jedec.org/standards-documents/docs/so-018a
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GDDR5M/DDR4 SODIMM standard coming soon for the PC.
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if it's almost identical latency why pc oem and apple doesn't make unified ram in their laptop just like ps4 ? i admire anandtech but i think apple & microsoft engineer have more experience with computer hardware than anandtech
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