Overclock.net › Forums › Components › Memory › Memory: Dividers, Latencies, and Bandwidth Explained
New Posts  All Forums:Forum Nav:

Memory: Dividers, Latencies, and Bandwidth Explained - Page 4

post #31 of 57
Thread Starter 
Quote:
Originally Posted by Litlratt View Post
If I understand this correctly, if both examples were running the same timings, then the latency would be the same.
If you can maintain tight timings and continually increase speed, then performance increases regardless of the divider.
No, the latencies that are incurred upon the memory system is dependent upon the speed of the memory and the timing of the latencies.
System
(13 items)
 
  
CPUMotherboardGraphicsRAM
Core i7 2500k ASRock P67 Extreme4 Gen 3 AMD 7970 16GB DDR3 
Hard DriveOptical DriveOSMonitor
Intel 520 256GB SATA DVD Burner Windows 7 64 bit Deal U2410 
KeyboardPowerMouse
Adesso Mechanical Silverstone OP650 Logitech G700 
  hide details  
Reply
System
(13 items)
 
  
CPUMotherboardGraphicsRAM
Core i7 2500k ASRock P67 Extreme4 Gen 3 AMD 7970 16GB DDR3 
Hard DriveOptical DriveOSMonitor
Intel 520 256GB SATA DVD Burner Windows 7 64 bit Deal U2410 
KeyboardPowerMouse
Adesso Mechanical Silverstone OP650 Logitech G700 
  hide details  
Reply
post #32 of 57
Quote:
Originally Posted by pauldovi View Post
No, the latencies that are incurred upon the memory system is dependent upon the speed of the memory and the timing of the latencies.
This is where I'm confused.
From your guide:
For example:

DDR2-800 does 800,000,000 cycles per second. Latencies of 4-4-4-12 add up to 24 cycles per operation of latency. Divide 24 cycles of latencies by 800,000,000 cycles and you get 30 nano-seconds worth of latencies per operation. However, DDR2-1000 with latencies of 5-5-5-15 also net you the same 30 nano-seconds of latencies per operation (30 / 1,000,000,000).

However, even though both settings have the same latencies. DDR2-1000 @ 5-5-5-15 is better than DDR2-800 @ 4-4-4-12, this is because DDR2-1000 has more data throughput when compared to DDR2-800.

If both examples are at 4 4 4 12 then that's 24 nano seconds regardless of speed. Where/how does the speed of the ram fall into the equation?

Rep+ for spending your time educating us paul. Thank you.
Trouble
(13 items)
 
  
CPUMotherboardGraphicsRAM
QX9650 EVGA 790i@P07 3X EVGA GTX280 4X 1GB OCZ DDR3 14400 
Hard DriveOptical DriveOSMonitor
2X 74GB Raptor Raid 0/(2)2X WD320 Raid 0 2X Samsung 18XDVDRW XP32/ViPre64/ViBas64 Dell 3007WFP 
KeyboardPowerCaseMouse
Saitek Cyborg TT TP 1200W Lian-Li 343B MS TBall Optical/MX Revolution 
  hide details  
Reply
Trouble
(13 items)
 
  
CPUMotherboardGraphicsRAM
QX9650 EVGA 790i@P07 3X EVGA GTX280 4X 1GB OCZ DDR3 14400 
Hard DriveOptical DriveOSMonitor
2X 74GB Raptor Raid 0/(2)2X WD320 Raid 0 2X Samsung 18XDVDRW XP32/ViPre64/ViBas64 Dell 3007WFP 
KeyboardPowerCaseMouse
Saitek Cyborg TT TP 1200W Lian-Li 343B MS TBall Optical/MX Revolution 
  hide details  
Reply
post #33 of 57
To further clarify that, the 1066 5-5-5-15 would have significantly lower latencies than the 800 5-5-5-15 all else being equal.

This is an ultra simplistic explanation (READ: total over-simplification) but:

30 clocks of latency is a variable amount of time. Look at it this way, a 'clock' is simply one period of the sine wave that the memory is running on.

If you're running 10Hz with 1 clock of waiting you now have 9 times per second that the ram is DOING stuff.

Now, if you're still running one clock of latency but now have ram running 20Hz, you now have 19 times per second your ram is DOING something.

1 clock of latency/10 clocks per second = 0.1s and 1 clock of latency/20 clocks per second = 0.025

So now your REAL latencies are at the given speeds are 0.1s and .025s, respectively. Theoretically doubling ram speed at the SAME latency will cut your REAL latency times by 75%.
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
post #34 of 57
Thread Starter 
Quote:
Originally Posted by Litlratt View Post
This is where I'm confused.
From your guide:
For example:

DDR2-800 does 800,000,000 cycles per second. Latencies of 4-4-4-12 add up to 24 cycles per operation of latency. Divide 24 cycles of latencies by 800,000,000 cycles and you get 30 nano-seconds worth of latencies per operation. However, DDR2-1000 with latencies of 5-5-5-15 also net you the same 30 nano-seconds of latencies per operation (30 / 1,000,000,000).

However, even though both settings have the same latencies. DDR2-1000 @ 5-5-5-15 is better than DDR2-800 @ 4-4-4-12, this is because DDR2-1000 has more data throughput when compared to DDR2-800.

If both examples are at 4 4 4 12 then that's 24 nano seconds regardless of speed. Where/how does the speed of the ram fall into the equation?

Rep+ for spending your time educating us paul. Thank you.
Well the example has the DDR2-1000 @ 5-5-5-15 and the DDR2-800 @ 4-4-4-12.

The way you compute latencies per operation is to add up the timings 4+4+4+12 = 24 and then divide by the operations per second (800,000,000)

24 / 800,000,000 = 30 nano seconds of latencies per operation

30 / 1,000,000,000 = 30 nano seconds of latencies per operation
System
(13 items)
 
  
CPUMotherboardGraphicsRAM
Core i7 2500k ASRock P67 Extreme4 Gen 3 AMD 7970 16GB DDR3 
Hard DriveOptical DriveOSMonitor
Intel 520 256GB SATA DVD Burner Windows 7 64 bit Deal U2410 
KeyboardPowerMouse
Adesso Mechanical Silverstone OP650 Logitech G700 
  hide details  
Reply
System
(13 items)
 
  
CPUMotherboardGraphicsRAM
Core i7 2500k ASRock P67 Extreme4 Gen 3 AMD 7970 16GB DDR3 
Hard DriveOptical DriveOSMonitor
Intel 520 256GB SATA DVD Burner Windows 7 64 bit Deal U2410 
KeyboardPowerMouse
Adesso Mechanical Silverstone OP650 Logitech G700 
  hide details  
Reply
post #35 of 57
Quote:
Originally Posted by pauldovi View Post
Well the example has the DDR2-1000 @ 5-5-5-15 and the DDR2-800 @ 4-4-4-12.

The way you compute latencies per operation is to add up the timings 4+4+4+12 = 24 and then divide by the operations per second (800,000,000)

24 / 800,000,000 = 30 nano seconds of latencies per operation

30 / 1,000,000,000 = 30 nano seconds of latencies per operation
I'll try again.
If both speeds of ram are running the same timings, then the faster ram not only has more bandwidth but is also has faster latencies.
So:
If you can maintain tight timings and continually increase speed, then performance increases regardless of the divider.
Trouble
(13 items)
 
  
CPUMotherboardGraphicsRAM
QX9650 EVGA 790i@P07 3X EVGA GTX280 4X 1GB OCZ DDR3 14400 
Hard DriveOptical DriveOSMonitor
2X 74GB Raptor Raid 0/(2)2X WD320 Raid 0 2X Samsung 18XDVDRW XP32/ViPre64/ViBas64 Dell 3007WFP 
KeyboardPowerCaseMouse
Saitek Cyborg TT TP 1200W Lian-Li 343B MS TBall Optical/MX Revolution 
  hide details  
Reply
Trouble
(13 items)
 
  
CPUMotherboardGraphicsRAM
QX9650 EVGA 790i@P07 3X EVGA GTX280 4X 1GB OCZ DDR3 14400 
Hard DriveOptical DriveOSMonitor
2X 74GB Raptor Raid 0/(2)2X WD320 Raid 0 2X Samsung 18XDVDRW XP32/ViPre64/ViBas64 Dell 3007WFP 
KeyboardPowerCaseMouse
Saitek Cyborg TT TP 1200W Lian-Li 343B MS TBall Optical/MX Revolution 
  hide details  
Reply
post #36 of 57
You will never get decreased performance from upping a divider ll else equal. However, if you have to choose between maxing your ram on the 3:2 divider and leaving your CPU 200 MHz short of its max and running the 200MHz more on your CPU and losing a 100-200MHz on your ram... ALWAYS pick the CPU speed.
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
post #37 of 57
Thread Starter 
Quote:
Originally Posted by Litlratt View Post
I'll try again.
If both speeds of ram are running the same timings, then the faster ram not only has more bandwidth but is also has faster latencies.
So:
If you can maintain tight timings and continually increase speed, then performance increases regardless of the divider.
Right.

The divider is just a way of comparing the FSB to the memory speed. It doesn't really mean anything.
System
(13 items)
 
  
CPUMotherboardGraphicsRAM
Core i7 2500k ASRock P67 Extreme4 Gen 3 AMD 7970 16GB DDR3 
Hard DriveOptical DriveOSMonitor
Intel 520 256GB SATA DVD Burner Windows 7 64 bit Deal U2410 
KeyboardPowerMouse
Adesso Mechanical Silverstone OP650 Logitech G700 
  hide details  
Reply
System
(13 items)
 
  
CPUMotherboardGraphicsRAM
Core i7 2500k ASRock P67 Extreme4 Gen 3 AMD 7970 16GB DDR3 
Hard DriveOptical DriveOSMonitor
Intel 520 256GB SATA DVD Burner Windows 7 64 bit Deal U2410 
KeyboardPowerMouse
Adesso Mechanical Silverstone OP650 Logitech G700 
  hide details  
Reply
post #38 of 57
You know, Pauldovi, I've been thinking that the ram latencies are not quite as additive as you say they are. I couldn't put my finger on why until I found this little baby. As you can see, ras and cas latencies overlap and are not directly additive.


http://arstechnica.com/paedia/r/ram_...e.part2-1.html
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
post #39 of 57
Quote:
Originally Posted by Ihatethedukes View Post
You know, Pauldovi, I've been thinking that the ram latencies are not quite as additive as you say they are. I couldn't put my finger on why until I found this little baby. As you can see, ras and cas latencies overlap and are not directly additive.

Which would imply CAS and tRAC produce the most latency? Am I interpreting that correctly???
TITAN-6
(16 items)
 
  
CPUMotherboardGraphicsRAM
i7 2600K @ 4GHZ ASRock Extreme 3 Gen 3 Gigabyte Nvidia GTX 570 8GB G.skill Sniper DDR3 1866 
Hard DriveOptical DriveCoolingOS
Crucial M4 CT128M4SSD2 2.5" 128GB SATA III MATSHITA BD-CMB UJ160 Blu Ray DVD writer Cooler Master Hyper 212+ Windows 7 x64 
MonitorMonitorKeyboardPower
Sceptre 24" LCD BENQ 3D 24" LCD Logitech G510 Corsair 750W HX professional single rail 
CaseMouseMouse PadAudio
CM Storm Sniper Razer Naga left-handed version None Onboard 
  hide details  
Reply
TITAN-6
(16 items)
 
  
CPUMotherboardGraphicsRAM
i7 2600K @ 4GHZ ASRock Extreme 3 Gen 3 Gigabyte Nvidia GTX 570 8GB G.skill Sniper DDR3 1866 
Hard DriveOptical DriveCoolingOS
Crucial M4 CT128M4SSD2 2.5" 128GB SATA III MATSHITA BD-CMB UJ160 Blu Ray DVD writer Cooler Master Hyper 212+ Windows 7 x64 
MonitorMonitorKeyboardPower
Sceptre 24" LCD BENQ 3D 24" LCD Logitech G510 Corsair 750W HX professional single rail 
CaseMouseMouse PadAudio
CM Storm Sniper Razer Naga left-handed version None Onboard 
  hide details  
Reply
post #40 of 57
Okay, this explains why tras doesn't matter very much in performance. The other three ratings do. They are the CAS latency, the RAS-to-CAS delay, the RAS precharge time and the Ras active.

If you look at the chart ras is activated and lasts a long time. However, before it is terminated, Cas is already activated (provided your ras active time is set to more than your ras to cas delay) and ras can last through the ras to cas delay PLUS the cas active without any significant detrimental effects to performance because it cannot be reactivated until CAS active is over. It does need to allow time to precharge ras before it can be activated again but that time is small. (3-5 clocks on today's DDR2) On 4-4-4-10 ram ras can be ras to cas delay + cas latency + cas active - ras precharge delay WITHOUT ANY REAL DETRIMENTAL EFFECT TO PERFORMANCE. So, 4+cas active clocks, which is memory serves me correctly is 4-8 bursts. Which makes sense with most ram being ras10.

It would seem that Cas + ras to cas delay introduce the most latency.
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
Raptor Raper
(13 items)
 
  
CPUMotherboardGraphicsRAM
Something with transistors FOXCONN Boodrage -> eVGA classified e760 GTX 480 / HD6850@1090/1200 3x2 gig G Skill Trident DDR2000 
Hard DriveOptical DriveOSMonitor
2x128GB Crucial C300 Sumsung SATA DVD-RW 64 bit Windows 7 Samsung 245BW 
KeyboardPowerCaseMouse
Microsoft curve Tagan ITZ 800W DD Torture Rack Diamondback 
  hide details  
Reply
New Posts  All Forums:Forum Nav:
  Return Home
  Back to Forum: Memory
Overclock.net › Forums › Components › Memory › Memory: Dividers, Latencies, and Bandwidth Explained