DDR Memory Module Analysis. Part 6: G.Skill DDR-500 Modules

We proceed with the series of articles, dedicated to the low level analysis of the most important characteristics of DDR memory modules using our RightMark Memory Analyzer test package. Today is the second time when we are going to review DDR memory modules of large capacity — a couple of high-speed G.Skill DDR-500 modules with the total capacity of 2 GB.

Manufacturer Information

Module manufacturer: G.Skill
Manufacturer of module chips: unknown
Web site of the module manufacturer: http://www.gskill.com/ddr.html

Module Exterior

Photo of the memory module

Module Part Number

The manufacturer's web site does not publish the DDR Part Number expansion. Brief description of these modules on the official web site specifies that this product is a matched pair of memory modules of the uncertified DDR-500 standard (PC4000). They are the first modules of the HZ series with the total capacity of 2 GB (hence, capacity of a single module is 1 GB). In this mode, the modules can operate with 3-4-4-8 timings at a relatively low voltage of 2.6-2.8 V.

SPD chip data

Description of the general SPD standard:
JEDEC Standard No. 21-C, 4.1.2 - SERIAL PRESENCE DETECT STANDARD, General Standard

Description of the specific SPD standard for DDR:
JEDEC Standard No. 21-C, 4.1.2.4 — Appendix D, Rev. 1.0: SPD’s for DDR SDRAM

Parameter	Bytes	Value	Expansion
Fundamental Memory Type	2	07h	DDR SDRAM
Number of Row Addresses on this assembly	3	0Dh	13 (RA0-RA12)
Number of Column Addresses on this assembly	4	0Bh	11 (CA0-CA10)
Number of DIMM Banks	5	02h	2 physical banks
Data Width of this assembly	6, 7	40h, 00h	64 bit
Voltage Interface Level of this assembly	8	04h	SSTL 2.5V
SDRAM Cycle time (t_CK) at maximum supported CAS# latency (CL X)	9	50h	4.0 ns (250.0 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	0Eh	BL = 2, 4, 8
Number of Banks on SDRAM Device	17	04h	4
CAS Latency (CL)	18	10h	CL = 3.0
Minimum clock cycle (t_CK) at reduced CAS# latency (CL X-0.5)	23	00h	Not defined
Minimum clock cycle (t_CK) at reduced CAS# latency (CL X-1.0)	25	00h	Not defined
Minimum Row Precharge Time (t_RP)	27	3Ch	15.0 ns 3.75 (4), CL = 3.0
Minimum Row Active to Row Active delay (t_RRD)	28	28h	10.0 ns 2.5, CL = 3.0
Minimum RAS to CAS delay (t_RCD)	29	3Ch	15.0 ns 3.75 (4), CL = 3.0
Minimum Active to Precharge Time (t_RAS)	30	20h	32.0 ns 8, CL = 3.0
Module Bank Density	31	80h	512 MB
SDRAM Device Minimum Active to Active/Auto Refresh Time (t_RC)	41	00h	Not defined
SDRAM Device Minimum Auto-Refresh to Active/Auto-Refresh Command Period (t_RFC)	42	00h	Not defined
Maximum device cycle time (t_CKmax)	43	00h	Not defined
SPD Revision	62	01h	Revision 0.1
Checksum for Bytes 0-62	63	AEh	174 (true)
Manufacturer’s JEDEC ID Code (only the first significant bytes are shown)	64-71	7Fh, 7Fh, 7Fh, 7Fh, CDh	Corsair
Module Part Number	73-90	—	HZ
Module Manufacturing Date	93-94	00h, 00h	Not defined
Module Serial Number	95-98	00h, 00h, 00h, 00h	Not defined

SPD contents do not look standard (not surprising, considering that these modules are not standard themselves). Only one CAS# latency is supported (CL X) = 3, which corresponds to the cycle time of 4.0 ns (operating in non-standard DDR-500 mode). The timing scheme corresponding to this only case looks somewhat strange, as it contains fractional t_RCD and t_RP — 3-3.75-3.75-8. Nevertheless, considering that most BIOS versions usually round up fractional values in memory settings, we get the 3-4-4-8 scheme, specified by the manufacturer. There is a shortcoming - no SPD information about timings for the standard DDR-400 mode, necessary for the system to set memory parameters correctly by default. This option should have been written for the reduced CAS# latency (CL X-0.5) — the proper scheme might have looked like 2.5-3-3-6.4 (rounded up to 2.5-3-3-7).

Among other SPD peculiarities we can mention undefined absolute values for t_RC and t_RFC and maximum device cycle time (t_CKmax), as well as a strange SPD revision "0.1" and no data on manufacturing date and serial number. What concerns Part Number, you can see that the corresponding text field indicates HZ series, but it does not contain a specific number of these modules.

Testbed configuration and software

CPU: AMD Athlon 64 4000+, 2.4 GHz (ClawHammer rev. SH-CG, 1 MB L2)
Chipset: NVIDIA nForce4 SLI X16
Motherboard: MSI K8N Diamond Plus, BIOS 080012 dated 12/22/2005
Memory: 2x1024 MB G.Skill PC4000, DDR-500 (in DDR-400 mode)
Video: Leadtek PX350 TDH, NVIDIA PCX5900
HDD: WD Raptor WD360, SATA, 10000 rpm, 36Gb
Drivers: NVIDIA Forceware 77.72, NVIDIA nForce4 X16 6.82, DirectX 9.0c

Test Results

Performance tests

The modules were tested in the standard mode — DDR-400. As usual, in the first series of tests memory timings were set by default (BIOS Setup — Memory Timings: "by SPD"). One of the motherboards, recommended by the module manufacturer and used in our tests, MSI K8N Diamond Plus, set its timings in this case to 3-3-3-7, which is somewhere between the official 3-4-4-8 scheme for DDR-500 and the proper DDR-400 scheme (mentioned above) — 2.5-3-3-7.

Parameter	G.Skill PC4000	Corsair XMS-3500LLPRO
Timings	3-3-3-7	2-3-2-6
Average memory read bandwidth, MB/sec	3916	4344
Average memory write bandwidth, MB/sec	2409	2555
Max. memory read bandwidth, MB/sec	6286	6400
Max. memory write bandwidth, MB/sec	6016	6213
Minimum Pseudo-Random Access Latency, ns	38.9	31.6
Maximum Pseudo-Random Access Latency, ns	42.2	35.3
Minimum Random Access Latency^*, ns	72.7	62.8
Maximum Random Access Latency^*, ns	76.5	67.0

^*16 MB block size

Speed characteristics of G.Skill modules look average (for comparison, the table contains the results of high-speed DDR modules Corsair XMS-3500LLPRO) — memory bandwidth is lower by about 100-200 MB/s, memory access latencies are higher by 7-10 ns compared to the modules specified.

Stability tests

Timing values, except for t_CL, were adjusted "on the fly" due to the built-in RMMA feature that allows to change dynamically memory settings supported by the chipset (in this case - by the memory controller integrated into Athlon 64). Memory operating stability was evaluated with an auxiliary utility RightMark Memory Stability Test, included into RMMA.

Parameter	G.Skill PC4000	Corsair XMS-3500LLPRO
Timings	2.5-3-3-5(-7-10)	2-3-2-5(-7-10)
Average memory read bandwidth, MB/sec	3917	4355
Average memory write bandwidth, MB/sec	2425	2572
Max. memory read bandwidth, MB/sec	6298	6410
Max. memory write bandwidth, MB/sec	6106	6211
Minimum Pseudo-Random Access Latency, ns	37.7	31.5
Maximum Pseudo-Random Access Latency, ns	41.1	35.3
Minimum Random Access Latency^*, ns	69.9	62.5
Maximum Random Access Latency^*, ns	73.6	66.7

^*16 MB block size

The new 1 GB memory modules on MSI K8N Diamond Plus allowed quite unassuming minimum timings in DDR-400 mode without losing stability — 2.5-3-3-5. That is we managed to reduce CAS# latency to just 2.5 (the last value, t_RAS, shouldn't be taken literally — as we know from our multiple reviews, most modules are indifferent to its changes).

The effect of overclocking timings is not high — we can notice some decrease in pseudo-random and random memory access latencies by about 1-3 ns.

Bottom line

G.Skill DDR-500 memory modules with the total capacity of 2 GB offer moderate performance characteristics and a moderate timings overclocking potential — minimal timings in DDR-400 mode are just 2.5-3-3-5. Considering that DDR modules of high capacity is a new trend — both for this manufacturer as well as for the industry on the whole, we can expect modules of this type with better characteristics in future.

Dmitri Besedin (dmitri_b@ixbt.com)
March 24, 2006

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