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Memory Module Analysis. Part 20: Corsair DDR2-1066 (XMS2-8500)

May 18, 2006




We proceed with the low-level analysis of the most important characteristics of high-performance DDR2 memory modules using our RightMark Memory Analyzer. Today we are going to review the first offer in the highest-speed unofficial category — DDR2-1066 (PC2-8500) — dual-channel kit of Corsair XMS2-8500 memory modules, a logical continuation of high-speed XMS2-series solutions. We have already reviewed XMS2-8000UL modules from this series of the DDR2-1000 class. Frankly speaking, DDR2-1066 solutions (for example, from A-DATA) have been nominally known from the middle of the last year. Nevertheless, our modules under review are the first offer on the market, which can really operate in the unofficial DDR2-1066 mode, that is with the memory bus clock of 533 MHz.

Manufacturer Information

Module manufacturer: Corsair Memory
Manufacturer of module chips: unknown
Web site of the module manufacturer:
http://www.corsairmemory.com/corsair/xms2.html

Module Exterior

Photo of the memory module




Module Part Number

Module Part Number Expansion




The manufacturer's web site does not publish the DDR2 Part Number expansion of XMS2-series memory modules. The booklet about TWIN2X1024-8500 specifies that this product is a kit of two 512MB modules (Module Part Number - CM2X512-8500), based on eight 64M x8 chips. The manufacturer guarantees operation of these modules in the fastest (so far unofficial) DDR2-1066 mode with 5-5-5-15 timings and 2.2 V voltage. But the default mode written in the SPD chip is the maximum standard mode - DDR2-800 with 5-5-5-15 timings.

SPD chip data

Description of the general SPD standard:

Description of the specific SPD standard for DDR2:

Parameter Byte Value Expansion
Fundamental Memory Type 2 08h DDR2 SDRAM
Number of Row Addresses on this assembly 3 0Eh 14 (RA0-RA13)
Number of Column Addresses on this assembly 4 0Ah 10 (CA0-CA9)
Number of DIMM Banks 5 60h 1 physical bank
Data Width of this assembly 6 40h 64 bit
Voltage Interface Level of this assembly 8 05h SSTL 1.8V
SDRAM Cycle time (tCK) at maximum supported CAS# latency (CL X) 9 30h 2.50 ns (400.0 MHz)
DIMM configuration type 11 00h Non-ECC
Refresh Rate/Type 12 82h 7.8125 ms — 0.5x reduced self-refresh
Primary SDRAM Width (organization type) of the memory module chips 13 08h x8
Error Checking SDRAM Width (organization type) of the memory chips in the ECC module 14 00h Not defined
Burst Lengths Supported (BL) 16 0Ch BL = 4, 8
Number of Banks on SDRAM Device 17 04h 4
CAS Latency (CL) 18 30h CL = 5, 4
Minimum clock cycle (tCK) at reduced CAS# latency (CL X-1) 23 37h 3.70 ns (270.3 MHz)
Minimum clock cycle (tCK) at reduced CAS# latency (CL X-2) 25 00h Not defined
Minimum Row Precharge Time (tRP) 27 32h 12.5 ns
5.0, CL = 5
3.37, CL = 4
Minimum Row Active to Row Active delay (tRRD) 28 1Eh 7.5 ns
3.0, CL = 5
2.03, CL = 4
Minimum RAS to CAS delay (tRCD) 29 32h 12.5 ns
5.0, CL = 5
3.37, CL = 4
Minimum Active to Precharge Time (tRAS) 30 2Dh 45.0 ns
18.0, CL = 5
12.16, CL = 4
Module Bank Density 31 80h 512 MB
Write recovery time (tWR) 36 3Ch 15.0 ns
6.0, CL = 5
4.05, CL = 4
Internal write to read command delay (tWTR) 37 1Eh 7.5 ns
3.0, CL = 5
2.03, CL = 4
Internal read to precharge command delay (tRTP) 38 1Eh 7.5 ns
3.0, CL = 5
2.03, CL = 4
SDRAM Device Minimum Active to Active/Auto Refresh Time (tRC) 41, 40 37h, 00h 55.0 ns
22.0, CL = 5
14.86, CL = 4
SDRAM Device Minimum Auto-Refresh to Active/Auto-Refresh Command Period (tRFC) 42, 40 69h, 00h 75.0 ns
30.0, CL = 5
20.27, CL = 4
Maximum device cycle time (tCKmax) 43 80h 8.0 ns
SPD Revision 62 12h Revision 1.2
Checksum for Bytes 0-62 63 97h 151 (true)
Manufacturer’s JEDEC ID Code 64-71 7Fh, 7Fh,
9Eh
Corsair
Module Part Number 73-90 CM2X512-8500
Module Manufacturing Date 93-94 00h, 00h Not defined
Module Serial Number 95-98 00h, 00h,
00h, 00h
Not defined

SPD data are not quite standard, but usual for Corsair modules. The fastest mode these modules are capable of is characterized by the cycle time of 2.5 ns (400 MHz, DDR2-800). This mode corresponds to the first supported value of tCL = 5, the full timing scheme is written as 5-5-5-18, which slightly disagrees with official characteristics, published in the datasheet on these modules (DDR2-800, 5-5-5-15). Reduced CAS# latency (CL X-1 = 4) corresponds to the non-standard cycle time of 3.7 ns, 270 MHz — it probably means DDR2-533 and the cycle time of 3.75 ns. Nevertheless, the incorrect cycle time results in fractional timings, which can be written (rounded to one figure after the dot) as 4-3.4-3.4-12.2, which will most likely be rounded up by most BIOS's to 4-4-4-13. Nevertheless, it should be noted that you will hardly need such a slow mode as DDR2-533 for these high-performance modules.

Manufacturer’s JEDEC ID Code and Part Number of the module are correct. Nevertheless, as in the other Corsair modules, the SPD chip of these modules lacks information about the manufacturing date and serial number.

Testbed configuration

  • CPU: Intel Pentium 4 Extreme Edition 3.73 GHz (Prescott N0, 2 MB L2)
  • Chipset: Intel 975X
  • Motherboard: ASUS P5WD2-E Premium, BIOS 0404 dated 03/22/2006
  • Memory: 2x512 MB Corsair XMS2-8500 (DDR2-1066, PC2-8500)

Test Results

Performance tests

From this review on we upgrade to RMMA 3.65 with increased size of the allocated memory block and consequently modified default parameters in the majority of subtests. In particular, the memory block size in subtests for analyzing memory characteristics has been increased to 32 MB to reduce the effect of large L2 Cache (2 MB), which is often used in modern processors of the Pentium 4/Pentium D class. In this respect, characteristics listed below are much more precise in reflecting real memory bandwidth values and cannot be compared on the quantitative level with characteristics, published in the earlier reviews.

As usual, in the first series of tests we used the timing scheme, set in BIOS Setup by default (Memory Timings: "by SPD"). The modules were tested in three modes — DDR2-667 with 200 MHz and 266 MHz FSB (memory multipliers - 1.67 and 1.25), DDR2-800 with 200 MHz and 266 MHz FSB (memory multipliers - 2.0 and 1.5), as well as unofficial "DDR2-1066" with 266 MHz FSB and the maximum memory multiplier possible - 2.0.

BIOS on the testbed set 5-5-5-15 timings by default for DDR2-667 ("at random", as this mode is not written in the SPD chip), DDR2-800 mode — 5-5-5-18 (strictly by SPD), and finally the fastest DDR2-1066 mode — 5-6-6-18. As we know from practice, it's the slowest timing scheme the ASUS P5WD2-E motherboard (we use it for testing high-speed memory modules) can set by default.

Parameter / Mode DDR2-667 DDR2-800 DDR2-1066
FSB Clock, MHz
200
266
200
266
266
Timings
5-5-5-15
5-5-5-15
5-5-5-18
5-5-5-18
5-6-6-18
Average memory read bandwidth, MB/sec
5382
6396
5614
6878
7394
Average memory write bandwidth, MB/sec
2001
2163
2175
2415
2861
Max. memory read bandwidth, MB/sec
6468
8148
6530
8527
8669
Max. memory write bandwidth, MB/sec
4282
5668
4279
5685
5697
Minimum Pseudo-Random Access Latency, ns
56.7
50.1
52.7
45.7
39.7
Maximum Pseudo-Random Access Latency, ns
66.2
57.4
61.9
53.2
46.9
Minimum Random Access Latency*, ns
118.4
105.2
105.7
95.4
84.1
Maximum Random Access Latency*, ns
143.4
123.1
130.5
114.8
102.4
Minimum Pseudo-Random Access Latency, ns
(without hardware prefetch)
87.1
77.9
80.6
70.7
60.6
Maximum Pseudo-Random Access Latency, ns
(without hardware prefetch)
114.1
97.2
106.9
91.0
80.5
Minimum Random Access Latency*, ns
(without hardware prefetch)
119.2
105.9
106.1
95.9
84.3
Maximum Random Access Latency*, ns
(without hardware prefetch)
145.5
124.7
133.4
116.0
103.2

*32 MB block size

These modules demonstrate good performance results — maximum memory bandwidth values in official modes are approximately 6.4-6.5 GB/s and 8.2-8.7 GB/s at the FSB clock of 200 MHz and 266 MHz correspondingly. That is they almost equal the maximum theoretical bandwidth of the 200 MHz and 266 MHz FSB (it's actually a tad higher due to the effect of 2 MB L2 Cache, which can "cover" 2MB/32MB * 100% = 6.25% of memory access). Note that the maximum real memory read bandwidth both with 200 MHz and 266 MHz FSB grows much when we go from DDR2-667 to the fastest DDR2-1066 mode.

These modules are also on a par with previous high-speed solutions from Corsair and other manufacturers in latencies. Together with the above mentioned increase in memory bandwidth, faster modes (going from DDR2-667 to DDR2-800 and DDR2-1066) as well as higher-clocked FSB (going from 200-MHz to 266-MHz FSB) result in noticeably lower latencies. So the minimum memory latency is demonstrated in DDR2-1066 mode (266 MHz FSB) - from 39.7ns (pseudo-random walks, hardware prefetch enabled) to 103.2ns (random walks, hardware prefetch disabled). It's a tad better than in the previous Corsair XMS2-8000UL (DDR2-1000, 250 MHz FSB, 5-6-6-18 timings) as well as in Kingston HyperX DDR2-900 (DDR2-900, 270 MHz FSB, 5-6-6-18 timings).

Stability tests

Timing values, except for tCL, were adjusted "on the fly" due to the built-in RMMA feature that allows to change dynamically memory settings supported by the chipset. Memory operating stability was evaluated with an auxiliary utility RightMark Memory Stability Test, included into RMMA.

Parameter / Mode DDR2-667 DDR2-800 DDR2-1067
FSB Clock, MHz
200
266
200
266
266
Timings
3-3-3
(2.2 V)
3-3-3
(2.2 V)
4-4-3
(2.2 V)
4-4-3
(2.2 V)
5-5-4
(2.2 V)
Average memory read bandwidth, MB/sec
5571
6825
5696
6971
7446
Average memory write bandwidth, MB/sec
2444
2519
2460
2518
3193
Max. memory read bandwidth, MB/sec
6528
8393
6542
8567
8712
Max. memory write bandwidth, MB/sec
4282
5678
4282
5686
5698
Minimum Pseudo-Random Access Latency, ns
52.8
45.8
49.1
44.6
39.6
Maximum Pseudo-Random Access Latency, ns
62.4
53.0
58.9
52.0
46.5
Minimum Random Access Latency*, ns
104.6
92.0
101.1
92.5
84.0
Maximum Random Access Latency*, ns
128.7
111.6
125.5
112.4
102.2
Minimum Pseudo-Random Access Latency, ns
(without hardware prefetch)
81.4
70.8
75.0
68.5
60.8
Maximum Pseudo-Random Access Latency, ns
(without hardware prefetch)
107.5
90.4
102.7
88.2
80.1
Minimum Random Access Latency*, ns
(without hardware prefetch)
104.8
92.3
101.0
92.8
84.3
Maximum Random Access Latency*, ns
(without hardware prefetch)
131.6
112.8
127.4
113.4
103.0

*32 MB block size

Minimum timings, we managed to obtain in DDR2-667 mode with the recommended increased voltage of 2.2 V, are just 3-3-3 (as usual, the last parameter tRAS does not participate in the overclocking scheme, as it's ignored). We managed to set the 3-3-2 scheme "on the fly", but it immediately resulted in failures. What concerns this parameter, our modules under review are outperformed by the previously tested Kingston HyperX DDR2-900 (3-3-2 timings at 2.0V) and, especially, by early Corsair XMS2-5400UL (as we know from practice, it demonstrates the highest overclocking potential — 3-2-2 timings at 2.1V).

Our memory modules operate well in DDR2-800 mode with 4-4-3 timings (the voltage is also 2.2V). Note that we managed to set the 4-3-3 timing scheme here as well, but it immediately resulted in errors. And again these modules are outperformed by the older Corsair XMS2-8000UL (minimum timings possible in DDR2-800 mode are — 4-3-3 at 2.2V) and Corsair XMS2-5400UL (4-3-2 timings at 2.1V).

And finally, operating in the fastest "native" mode DDR2-1066, these modules allowed to set the minimum timing scheme - 5-5-4. Not bad actually, as it's a tad lower than the 5-5-5(-15) scheme, published by the manufacturer. At the same time, we should remember that the previous solution from Corsair — DDR2-1000 modules could operate in this mode with 5-3-3 timings.

As usual, "extreme" timings only insignificantly increase memory bandwidth, as it's still limited by FSB bandwidth. Maximum effect of overclocking timings is noticeable only in terms of latencies, only in case of random memory access and DDR2-667 mode (the best at overclocking) at that — latencies are reduced by 10% here.

Bottom line

Corsair XMS2-8500 proved to be high-performance high-end modules, which can operate in the official DDR2-667 and DDR2-800 modes as well as in the unofficial fastest DDR2-1066 mode (at the moderately high voltage of 2.2V). Note that these are the first modules, which are really designed for DDR2-1066 and which operation in this mode is really stable. These modules demonstrate high performance results, but relatively moderate overclocking potential of timings (compared to the early top offers from Corsair) — in official DDR2-667 and DDR2-800 modes they can operate with 3-3-3 and 4-4-3 timings (voltage - 2.2V), while the fastest DDR2-1066 mode requires increasing this scheme to 5-5-4, actually a tad lower compared to the recommended 5-5-5-15 scheme.


Dmitri Besedin (dmitri_b@ixbt.com)
May 18, 2006



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