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Serial presence detect

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In computing, serial presence detect (SPD) is a standardized way to automatically access information about a memory module. Earlier 72-pin SIMMs included five pins that provided five bits of parallel presence detect (PPD) data, but the 168-pin DIMM standard changed to a serial presence detect to encode more information.[1]

When an ordinary modern computer is turned on, it starts by doing a power-on self-test (POST). Since about the mid-1990s, this process includes automatically configuring the hardware currently present. SPD is a memory hardware feature that makes it possible for the computer to know what memory is present, and what memory timings to use to access the memory.

Some computers adapt to hardware changes completely automatically. In most cases, there is a special optional procedure for accessing BIOS parameters, to view and potentially make changes in settings. It may be possible to control how the computer uses the memory SPD data—to choose settings, selectively modify memory timings, or possibly to completely override the SPD data (see overclocking).

Stored information

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For a memory module to support SPD, the JEDEC standards require that certain parameters be in the lower 128 bytes of an EEPROM located on the memory module. These bytes contain timing parameters, manufacturer, serial number and other useful information about the module. Devices utilizing the memory automatically determine key parameters of the module by reading this information. For example, the SPD data on an SDRAM module might provide information about the CAS latency so the system can set this correctly without user intervention.

The SPD EEPROM firmware is accessed using SMBus, a variant of the I2C protocol. This reduces the number of communication pins on the module to just two: a clock signal and a data signal. The EEPROM shares ground pins with the RAM, has its own power pin, and has three additional pins (SA0–2) to identify the slot, which are used to assign the EEPROM a unique address in the range 0x50–0x57. Not only can the communication lines be shared among 8 memory modules, the same SMBus is commonly used on motherboards for system health monitoring tasks such as reading power supply voltages, CPU temperatures, and fan speeds.

SPD EEPROMs also respond to I2C addresses 0x30–0x37 if they have not been write protected, and an extension (TSE series) uses addresses 0x18–0x1F to access an optional on-chip temperature sensor. All those values are seven-bit I2C addresses formed by a Device Type Identifier Code prefix (DTIC) with SA0-2: to read (1100) from slot 3, one uses 110 0011 = 0x33. With a final R/W bit it forms the 8-bit Device Select Code.[2] Note that the semantics of slot-id is different for write-protection operations: for them they can be not passed by the SA pins at all.[3]

Before SPD, memory chips were spotted with parallel presence detect (PPD). PPD used a separate pin for each bit of information, which meant that only the speed and density of the memory module could be stored because of the limited space for pins.

SDR SDRAM

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Memory device on an SDRAM module, containing SPD data (red circled)

The first SPD specification was issued by JEDEC and tightened up by Intel as part of its PC100 memory specification introduced in 1998.[4][5][6] Most values specified are in binary-coded decimal form. The most significant nibble can contain values from 10 to 15, and in some cases extends higher. In such cases, the encodings for 1, 2 and 3 are instead used to encode 16, 17 and 18. A most significant nibble of 0 is reserved to represent "undefined".

The SPD ROM defines up to three DRAM timings, for three CAS latencies specified by set bits in byte 18. First comes the highest CAS latency (fastest clock), then two lower CAS latencies with progressively lower clock speeds.

SPD contents for SDR SDRAM[7]
Byte Bit Notes
(dec.) (hex.) 7 6 5 4 3 2 1 0
0 0x00 Number of bytes present Typically 128
1 0x01 log2(size of SPD EEPROM) Typically 8 (256 bytes)
2 0x02 Basic memory type (4: SPD SDRAM)
3 0x03 Bank 2 row address bits (0–15) Bank 1 row address bits (1–15) Bank 2 is 0 if same as bank 1
4 0x04 Bank 2 column address bits (0–15) Bank 1 column address bits (1–15) Bank 2 is 0 if same as bank 1
5 0x05 Number of RAM banks on module (1–255) Commonly 1 or 2
6 0x06 Module data width low byte Commonly 64, or 72 for ECC DIMMs
7 0x07 Module data width high byte 0, unless width ≥ 256 bits
8 0x08 Interface voltage level of this assembly (not the same as Vcc supply voltage) (0–4) Decoded by table lookup
9 0x09 Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Clock cycle time at highest CAS latency
10 0x0a Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) SDRAM access time from clock (tAC)
11 0x0b DIMM configuration type (0–2): non-ECC, parity, ECC Table lookup
12 0x0c Self Refresh period (0–5): 64, 256, 128, 32, 16, 8 kHz Refresh requirements
13 0x0d Bank 2 2× Bank 1 primary SDRAM width (1–127, usually 8) Width of bank 1 data SDRAM devices. Bank 2 may be same width, or 2× width if bit 7 is set.
14 0x0e Bank 2 2× Bank 1 ECC SDRAM width (0–127) Width of bank 1 ECC/parity SDRAM devices. Bank 2 may be same width, or 2× width if bit 7 is set.
15 0x0f Clock delay for random column reads Typically 1
16 0x10 Page — — — 8 4 2 1 Burst lengths supported (bitmap)
17 0x11 Banks per SDRAM device (1–255) Typically 2 or 4
18 0x12 — 7 6 5 4 3 2 1 CAS latencies supported (bitmap)
19 0x13 — 6 5 4 3 2 1 0 CS latencies supported (bitmap)
20 0x14 — 6 5 4 3 2 1 0 WE latencies supported (bitmap)
21 0x15 — Redundant Diff. clock Registered data Buffered data On-card PLL Registered addr. Buffered addr. Memory module feature bitmap
22 0x16 — — Upper Vcc (supply voltage) tolerance Lower Vcc (supply voltage) tolerance Write/1 read burst Precharge all Auto-precharge Early RAS precharge Memory chip feature support bitmap
23 0x17 Nanoseconds (4–18) Tenths of nanoseconds (0–9: 0.0–0.9) Clock cycle time at medium CAS latency
24 0x18 Nanoseconds (4–18) Tenths of nanoseconds (0–9: 0.0–0.9) Data access time from clock (tAC)
25 0x19 Nanoseconds (1–63) 0.25 ns (0–3: 0.00–0.75) Clock cycle time at short CAS latency.
26 0x1a Nanoseconds (1–63) 0.25 ns (0–3: 0.00–0.75) Data access time from clock (tAC)
27 0x1b Nanoseconds (1–255) Minimum row precharge time (tRP)
28 0x1c Nanoseconds (1–255) Minimum row active–row active delay (tRRD)
29 0x1d Nanoseconds (1–255) Minimum RAS to CAS delay (tRCD)
30 0x1e Nanoseconds (1–255) Minimum active to precharge time (tRAS)
31 0x1f 512 MiB 256 MiB 128 MiB 64 MiB 32 MiB 16 MiB 8 MiB 4 MiB Module bank density (bitmap). Two bits set if different size banks.
32 0x20 Sign (1: −) Nanoseconds (0–7) Tenths of nanoseconds (0–9: 0.0–0.9) Address/command setup time from clock
33 0x21 Sign (1: −) Nanoseconds (0–7) Tenths of nanoseconds (0–9: 0.0–0.9) Address/command hold time after clock
34 0x22 Sign (1: −) Nanoseconds (0–7) Tenths of nanoseconds (0–9: 0.0–0.9) Data input setup time from clock
35 0x23 Sign (1: −) Nanoseconds (0–7) Tenths of nanoseconds (0–9: 0.0–0.9) Data input hold time after clock
36–61 0x24–0x3d Reserved For future standardization
62 0x3e Major revision (0–9) Minor revision (0–9) SPD revision level; e.g., 1.2
63 0x3f Checksum Sum of bytes 0–62, not then negated
64–71 0x40–47 Manufacturer JEDEC id. Stored little-endian, trailing zero-padded
72 0x48 Module manufacturing location Vendor-specific code
73–90 0x49–0x5a Module part number ASCII, space-padded
91–92 0x5b–0x5c Module revision code Vendor-specific code
93 0x5d Tens of years (0–9: 0–90) Years (0–9) Manufacturing date (YYWW)
94 0x5e Tens of weeks (0–5: 0–50) Weeks (0–9)
95–98 0x5f–0x62 Module serial number Vendor-specific code
99–125 0x63–0x7f Manufacturer-specific data Could be enhanced performance profile
126 0x7e 0x66 [sic] for 66 MHz, 0x64 for 100 MHz Intel frequency support
127 0x7f CLK0 CLK1 CLK3 CLK3 90/100 °C CL3 CL2 Concurrent AP Intel feature bitmap

DDR SDRAM

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The DDR DIMM SPD format is an extension of the SDR SDRAM format. Mostly, parameter ranges are rescaled to accommodate higher speeds.

SPD contents for DDR SDRAM[8]
Byte Bit Notes
(dec.) (hex.) 7 6 5 4 3 2 1 0
0 0x00 Number of bytes written Typically 128
1 0x01 log2(size of SPD EEPROM) Typically 8 (256 bytes)
2 0x02 Basic memory type (7 = DDR SDRAM)
3 0x03 Bank 2 row address bits (0–15) Bank 1 row address bits (1–15) Bank 2 is 0 if same as bank 1.
4 0x04 Bank 2 column address bits (0–15) Bank 1 column address bits (1–15) Bank 2 is 0 if same as bank 1.
5 0x05 Number of RAM banks on module (1–255) Commonly 1 or 2
6 0x06 Module data width low byte Commonly 64, or 72 for ECC DIMMs
7 0x07 Module data width high byte 0, unless width ≥ 256 bits
8 0x08 Interface voltage level of this assembly (not the same as Vcc supply voltage) (0–5) Decoded by table lookup
9 0x09 Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Clock cycle time at highest CAS latency.
10 0x0a Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) SDRAM access time from clock (tAC)
11 0x0b DIMM configuration type (0–2): non-ECC, parity, ECC Table lookup
12 0x0c Self Refresh period (0–5): 64, 256, 128, 32, 16, 8 kHz Refresh requirements
13 0x0d Bank 2 2× Bank 1 primary SDRAM width (1–127) Width of bank 1 data SDRAM devices. Bank 2 may be same width, or 2× width if bit 7 is set.
14 0x0e Bank 2 2× Bank 1 ECC SDRAM width (0–127) Width of bank 1 ECC/parity SDRAM devices. Bank 2 may be same width, or 2× width if bit 7 is set.
15 0x0f Clock delay for random column reads Typically 1
16 0x10 Page — — — 8 4 2 1 Burst lengths supported (bitmap)
17 0x11 Banks per SDRAM device (1–255) Typically 4
18 0x12 — 4 3.5 3 2.5 2 1.5 1 CAS latencies supported (bitmap)
19 0x13 — 6 5 4 3 2 1 0 CS latencies supported (bitmap)
20 0x14 — 6 5 4 3 2 1 0 WE latencies supported (bitmap)
21 0x15 — x Diff clock FET switch external enable FET switch on-board enable On-card PLL Registered Buffered Memory module feature bitmap
22 0x16 Fast AP Concurrent auto precharge Upper Vcc (supply voltage) tolerance Lower Vcc (supply voltage) tolerance — — — Includes weak driver Memory chip feature bitmap
23 0x17 Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Clock cycle time at medium CAS latency.
24 0x18 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data access time from clock (tAC)
25 0x19 Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Clock cycle time at short CAS latency.
26 0x1a Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data access time from clock (tAC)
27 0x1b Nanoseconds (1–63) 0.25 ns (0–0.75) Minimum row precharge time (tRP)
28 0x1c Nanoseconds (1–63) 0.25 ns (0–0.75) Minimum row active–row active delay (tRRD)
29 0x1d Nanoseconds (1–63) 0.25 ns (0–0.75) Minimum RAS to CAS delay (tRCD)
30 0x1e Nanoseconds (1–255) Minimum active to precharge time (tRAS)
31 0x1f 512 MiB 256 MiB 128 MiB 64 MiB 32 MiB 16 MiB/
4 GiB		 8 MiB/
2 GiB		 4 MiB/
1 GiB		 Module bank density (bitmap). Two bits set if different size banks.
32 0x20 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Address/command setup time from clock
33 0x21 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Address/command hold time after clock
34 0x22 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data input setup time from clock
35 0x23 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data input hold time after clock
36–40 0x24–0x28 Reserved Superset information
41 0x29 Nanoseconds (1–255) Minimum active to active/refresh time (tRC)
42 0x2a Nanoseconds (1–255) Minimum refresh to active/refresh time (tRFC)
43 0x2b Nanoseconds (1–63, or 255: no maximum) 0.25 ns (0–0.75) Maximum clock cycle time (tCK max.)
44 0x2c Hundredths of nanoseconds (0.01–2.55) Maximum skew, DQS to any DQ. (tDQSQ max.)
45 0x2d Tenths of nanoseconds (0.0–1.2) Hundredths of nanoseconds (0.00–0.09) Read data hold skew factor (tQHS)
46 0x2e Reserved For future standardization
47 0x2f — Height Height of DIMM module, table lookup
48–61 0x30–0x3d Reserved For future standardization
62 0x3e Major revision (0–9) Minor revision (0–9) SPD revision level, 0.0 or 1.0
63 0x3f Checksum Sum of bytes 0–62, not then negated
64–71 0x40–47 Manufacturer JEDEC id. Stored little-endian, trailing zero-padded
72 0x48 Module manufacturing location Vendor-specific code
73–90 0x49–0x5a Module part number ASCII, space-padded
91–92 0x5b–0x5c Module revision code Vendor-specific code
93 0x5d Tens of years (0–90) Years (0–9) Manufacturing date (YYWW)
94 0x5e Tens of weeks (0–50) Weeks (0–9)
95–98 0x5f–0x62 Module serial number Vendor-specific code
99–127 0x63–0x7f Manufacturer-specific data Could be enhanced performance profile

DDR2 SDRAM

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The DDR2 SPD standard makes a number of changes, but is roughly similar to the above. One notable deletion is the confusing and little-used support for DIMMs with two ranks of different sizes.

For cycle time fields (bytes 9, 23, 25 and 49), which are encoded in BCD, some additional encodings are defined for the tenths digit to represent some common timings exactly:

DDR2 BCD extensions
Hex Binary Significance
A 1010 0.25 (1⁄4)
B 1011 0.33 (1⁄3)
C 1100 0.66 (2⁄3)
D 1101 0.75 (3⁄4)
E 1110 0.875 (7⁄8, Nvidia XMP extension)
F 1111 Reserved
SPD contents for DDR2 SDRAM[9]
Byte Bit Notes
Dec Hex 7 6 5 4 3 2 1 0
0 0x00 Number of bytes written Typically 128
1 0x01 log2(size of SPD EEPROM) Typically 8 (256 bytes)
2 0x02 Basic memory type (8 = DDR2 SDRAM)
3 0x03 Reserved Row address bits (1–15)
4 0x04 Reserved Column address bits (1–15)
5 0x05 Vertical height Stack? ConC? Ranks−1 (1–8) Commonly 0 or 1, meaning 1 or 2
6 0x06 Module data width Commonly 64, or 72 for ECC DIMMs
7 0x07 Reserved
8 0x08 Interface voltage level of this assembly (not the same as Vcc supply voltage) (0–5) Decoded by table lookup.
Commonly 5 = SSTL 1.8 V
9 0x09 Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Clock cycle time at highest CAS latency.
10 0x0a Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) SDRAM access time from clock (tAC)
11 0x0b DIMM configuration type (0–2): non-ECC, parity, ECC Table lookup
12 0x0c Self Refresh period (0–5): 64, 256, 128, 32, 16, 8 kHz Refresh requirements
13 0x0d Primary SDRAM width (1–255) Commonly 8 (module built from ×8 parts) or 16
14 0x0e ECC SDRAM width (0–255) Width of bank ECC/parity SDRAM devices. Commonly 0 or 8.
15 0x0f Reserved
16 0x10 — — — — 8 4 — — Burst lengths supported (bitmap)
17 0x11 Banks per SDRAM device (1–255) Typically 4 or 8
18 0x12 7 6 5 4 3 2 — — CAS latencies supported (bitmap)
19 0x13 Reserved
20 0x14 — — Mini-UDIMM Mini-RDIMM Micro-DIMM SO-DIMM UDIMM RDIMM DIMM type of this assembly (bitmap)
21 0x15 — Module is analysis probe — FET switch external enable — — — — Memory module feature bitmap
22 0x16 — — — — — — — Includes weak driver Memory chip feature bitmap
23 0x17 Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Clock cycle time at medium CAS latency.
24 0x18 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data access time from clock (tAC)
25 0x19 Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Clock cycle time at short CAS latency.
26 0x1a Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data access time from clock (tAC)
27 0x1b Nanoseconds (1–63) 1/4 ns (0–0.75) Minimum row precharge time (tRP)
28 0x1c Nanoseconds (1–63) 1/4 ns (0–0.75) Minimum row active–row active delay (tRRD)
29 0x1d Nanoseconds (1–63) 1/4 ns (0–0.75) Minimum RAS to CAS delay (tRCD)
30 0x1e Nanoseconds (1–255) Minimum active to precharge time (tRAS)
31 0x1f 512 MiB 256 MiB 128 MiB 16 GiB 8 GiB 4 GiB 2 GiB 1 GiB Size of each rank (bitmap).
32 0x20 Tenths of nanoseconds (0.0–1.2) Hundredths of nanoseconds (0.00–0.09) Address/command setup time from clock
33 0x21 Tenths of nanoseconds (0.0–1.2) Hundredths of nanoseconds (0.00–0.09) Address/command hold time after clock
34 0x22 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data input setup time from strobe
35 0x23 Tenths of nanoseconds (0.0–0.9) Hundredths of nanoseconds (0.00–0.09) Data input hold time after strobe
36 0x24 Nanoseconds (1–63) 0.25 ns (0–0.75) Minimum write recovery time (tWR)
37 0x25 Nanoseconds (1–63) 0.25 ns (0–0.75) Internal write to read command delay (tWTR)
38 0x26 Nanoseconds (1–63) 0.25 ns (0–0.75) Internal read to precharge command delay (tRTP)
39 0x27 Reserved Reserved for "memory analysis probe characteristics"
40 0x28 — tRC fractional ns (0–5):
0, 0.25, 0.33, 0.5, 0.66, 0.75		 tRFC fractional ns (0–5):
0, 0.25, 0.33, 0.5, 0.66, 0.75		 tRFC + 256 ns Extension of bytes 41 and 42.
41 0x29 Nanoseconds (1–255) Minimum active to active/refresh time (tRC)
42 0x2a Nanoseconds (1–255) Minimum refresh to active/refresh time (tRFC)
43 0x2b Nanoseconds (0–15) Tenths of nanoseconds (0.0–0.9) Maximum clock cycle time (tCK max)
44 0x2c Hundredths of nanoseconds (0.01–2.55) Maximum skew, DQS to any DQ. (tDQSQ max)
45 0x2d Hundredths of nanoseconds (0.01–2.55) Read data hold skew factor (tQHS)
46 0x2e Microseconds (1–255) PLL relock time
47–61 0x2f–0x3d Reserved For future standardization.
62 0x3e Major revision (0–9) Minor revision (0.0–0.9) SPD revision level, usually 1.0
63 0x3f Checksum Sum of bytes 0–62, not negated
64–71 0x40–47 Manufacturer JEDEC ID Stored little-endian, trailing zero-pad
72 0x48 Module manufacturing location Vendor-specific code
73–90 0x49–0x5a Module part number ASCII, space-padded (limited to (,-,), A–Z, a–z, 0–9, space)
91–92 0x5b–0x5c Module revision code Vendor-specific code
93 0x5d Years since 2000 (0–255) Manufacturing date (YYWW)
94 0x5e Weeks (1–52)
95–98 0x5f–0x62 Module serial number Vendor-specific code
99–127 0x63–0x7f Manufacturer-specific data Could be enhanced performance profile

DDR3 SDRAM

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The DDR3 SDRAM standard significantly overhauls and simplifies the SPD contents layout. Instead of a number of BCD-encoded nanosecond fields, some "timebase" units are specified to high precision, and various timing parameters are encoded as multiples of that base unit.[10] Further, the practice of specifying different time values depending on the CAS latency has been dropped; now there are just a single set of timing parameters.

Revision 1.1 lets some parameters be expressed as a "medium time base" value plus a (signed, −128 +127) "fine time base" correction. Generally, the medium time base is 1/8 ns (125 ps), and the fine time base is 1, 2.5 or 5 ps. For compatibility with earlier versions that lack the correction, the medium time base number is usually rounded up and the correction is negative. Values that work this way are:

DDR3 SPD two-part timing parameters
MTB byte FTB byte Value
12 34 tCKmin, minimum clock period
16 35 tAAmin, minimum CAS latency time
18 36 tRCDmin, minimum RAS# to CAS# delay
20 37 tRPmin, minimum row precharge delay
21, 23 38 tRCmin, minimum active to active/precharge delay
SPD contents for DDR3 SDRAM[11][12]
Byte Bit Notes
Dec Hex 7 6 5 4 3 2 1 0
0 0x00 Exclude serial from CRC SPD bytes total (undef/256) SPD bytes used (undef/128/176/256)
1 0x01 SPD major revision SPD minor revision 1.0, 1.1, 1.2 or 1.3
2 0x02 Basic memory type (11 = DDR3 SDRAM) Type of RAM chips
3 0x03 Reserved Module type Type of module; e.g., 2 = Unbuffered DIMM, 3 = SO-DIMM, 11=LRDIMM
4 0x04 — Bank address bits−3 log2(bits per chip)−28 Zero means 8 banks, 256 Mibit.
5 0x05 — Row address bits−12 Column address bits−9
6 0x06 Reserved 1.25 V 1.35 V Not 1.5 V Modules voltages supported. 1.5 V is default.
7 0x07 — ranks−1 log2(I/O bits/chip)−2 Module organization
8 0x08 — ECC bits (001=8) log2(data bits)−3 0x03 for 64-bit, non-ECC DIMM.
9 0x09 Dividend, picoseconds (1–15) Divisor, picoseconds (1–15) Fine Time Base, dividend/divisor
10 0x0a Dividend, nanoseconds (1–255) Medium Time Base, dividend/divisor; commonly 1/8
11 0x0b Divisor, nanoseconds (1–255)
12 0x0c Minimum cycle time tCKmin In multiples of MTB
13 0x0d Reserved
14 0x0e 11 10 9 8 7 6 5 4 CAS latencies supported (bitmap)
15 0x0f — 18 17 16 15 14 13 12
16 0x10 Minimum CAS latency time, tAAmin In multiples of MTB; e.g., 80/8 ns.
17 0x11 Minimum write recovery time, tWRmin In multiples of MTB; e.g., 120/8 ns.
18 0x12 Minimum RAS to CAS delay time, tRCDmin In multiples of MTB; e.g., 100/8 ns.
19 0x13 Minimum row to row active delay time, tRRDmin In multiples of MTB; e.g., 60/8 ns.
20 0x14 Minimum row precharge time, tRPmin In multiples of MTB; e.g., 100/8 ns.
21 0x15 tRCmin, bits 11:8 tRASmin, bits 11:8 Upper 4 bits of bytes 23 and 22
22 0x16 Minimum active to time, tRASmin, bits 7:0 In multiples of MTB; e.g., 280/8 ns.
23 0x17 Minimum active to active/refresh, tRCmin, bits 7:0 In multiples of MTB; e.g., 396/8 ns.
24 0x18 Minimum refresh recovery delay, tRFCmin, bits 7:0 In multiples of MTB; e.g., 1280/8 ns.
25 0x19 Minimum refresh recovery delay, tRFCmin, bits 15:8
26 0x1a Minimum internal write to read delay, tWTRmin In multiples of MTB; e.g., 60/8 ns.
27 0x1b Minimum internal read to precharge delay, tRTPmin In multiples of MTB; e.g., 60/8 ns.
28 0x1c Reserved tFAWmin, bits 11:8 In multiples of MTB; e.g., 240/8 ns.
29 0x1d Minimum four activate window delay tFAWmin, bits 7:0
30 0x1e DLL-off — RZQ/7 RZQ/6 SDRAM optional features support bitmap
31 0x1f PASR — ODTS ASR ETR 1× ETR (95 °C) SDRAM thermal and refresh options
32 0x20 Present Accuracy (TBD; currently 0 = undefined) DIMM thermal sensor present?
33 0x21 Nonstd. Die count — Signal load Nonstandard SDRAM device type (e.g., stacked die)
34 0x22 tCKmin correction (new for 1.1) Signed multiple of FTB, added to byte 12
35 0x23 tAAmin correction (new for 1.1) Signed multiple of FTB, added to byte 16
36 0x24 tRCDmin correction (new for 1.1) Signed multiple of FTB, added to byte 18
37 0x25 tRPmin correction (new for 1.1) Signed multiple of FTB, added to byte 20
38 0x26 tRCmin correction (new for 1.1) Signed multiple of FTB, added to byte 23
39–40 0x27–0x28 Reserved For future standardization.
41 0x29 Vendor specific tMAW Maximum Activate Count (MAC) (untested/700k/600k/.../200k/reserved/∞) For row hammer mitigation
42–59 0x2a–0x3b Reserved For future standardization.
60 0x3c — Module height, mm (1–31, >45) Module nominal height
61 0x3d Back thickness, mm (1–16) Front thickness, mm (1–16) Module thickness, value = ceil(mm) − 1
62 0x3e Design Revision JEDEC design number JEDEC reference design used (11111=none)
63–116 0x3f–0x74 Module-specific section Differs between registered/unbuffered
117 0x75 Module manufacturer ID, lsbyte Assigned by JEP-106
118 0x76 Module manufacturer ID, msbyte
119 0x77 Module manufacturing location Vendor-specific code
120 0x78 Tens of years Years Manufacturing year (BCD)
121 0x79 Tens of weeks Weeks Manufacturing week (BCD)
122–125 0x7a–0x7d Module serial number Vendor-specific code
126–127 0x7e–0x7f SPD CRC-16 Includes bytes 0–116 or 0–125; see byte 0 bit 7
128–145 0x80–0x91 Module part number ASCII subset, space-padded
146–147 0x92–0x93 Module revision code Vendor-defined
148–149 0x94–0x95 DRAM manufacturer ID As distinct from module manufacturer
150–175 0x96–0xAF Manufacturer-specific data
176–255 0xB0–0xFF Available for customer use

The memory capacity of a module can be computed from bytes 4, 7 and 8. The module width (byte 8) divided by the number of bits per chip (byte 7) gives the number of chips per rank. That can then be multiplied by the per-chip capacity (byte 4) and the number of ranks of chips on the module (usually 1 or 2, from byte 7).

DDR4 SDRAM

[edit]

The DDR4 SDRAM "Annex L" standard for SPD changes the EEPROM module used. Instead of the old AT24C02-compatible 256-byte EEPROMs, JEDEC now defines a new nonstandard EE1004 type with two pages at the SMBus level each with 256 bytes. The new memory still uses the old 0x50–0x57 addresses, but two additional address at 0x36 (SPA0) and 0x37 (SPA1) are now used to receive commands to select the currently-active page for the bus, a form of bank switching.[13] Internally each logical page is further divided into two physical blocks of 128 bytes each, totaling four blocks and 512 bytes.[14] Other semantics for "special" address ranges remain the same, although write protection is now addressed by blocks and a high voltage at SA0 is now required to change its status.[15]

Annex L defines a few different layouts that can be plugged into a 512-byte (of which a maximum of 320 bytes are defined) template, depending on the type of the memory module. The bit definitions are similar to DDR3.[14]

SPD contents for DDR4 SDRAM[16]
Byte Bit Notes
Dec Hex 7 6 5 4 3 2 1 0
0 0x00 SPD bytes used
1 0x01 SPD revision n Typically 0x10, 0x11, 0x12
2 0x02 Basic memory type (12 = DDR4 SDRAM) Type of RAM chips
3 0x03 Reserved Module type Type of module; e.g., 2 = Unbuffered DIMM, 3 = SO-DIMM, 11=LRDIMM
4 0x04 Bank group bits Bank address bits−2 Total SDRAM capacity per die in megabits Zero means no bank groups, 4 banks, 256 Mibit.
5 0x05 Reserved Row address bits−12 Column address bits−9
6 0x06 Primary SDRAM package type Die count Reserved Signal loading
7 0x07 Reserved Maximum activate window (tMAW) Maximum activate count (MAC) SDRAM optional features
8 0x08 Reserved SDRAM thermal and refresh options
9 0x09 Post package repair (PPR) Soft PPR Reserved Other SDRAM optional features
10 0x0a SDRAM package type Die count−1 DRAM density ratio Signal loading Secondary SDRAM package type
11 0x0b Reserved Endurant flag Operable flag Module nominal voltage, VDD
12 0x0c Reserved Rank mix Package ranks per DIMM−1 SDRAM device width Module organization
13 0x0d Reserved Bus width extension Primary bus width Module memory bus width in bits
14 0x0e Thermal sensor Reserved Module thermal sensor
15 0x0f Reserved Extended base module type
16 0x10 Reserved
17 0x11 Reserved Medium timebase (MTB) Fine timebase (FTB) Measured in ps.
18 0x12 Minimum SDRAM cycle time, tCKAVGmin In multiples of MTB; e.g., 100/8 ns.
19 0x13 Maximum SDRAM cycle time, tCKAVGmax In multiples of MTB; e.g., 60/8 ns.
20 0x14 14 13 12 11 10 9 8 7 CAS latencies supported bit-mask
21 0x15 22 21 20 19 18 17 16 15 CAS latencies supported bit-mask
22 0x16 30 29 28 27 26 25 24 23 CAS latencies supported bit-mask
23 0x17 Low CL range Reserved 36 35 34 33 32 31 CAS latencies supported bit-mask
24 0x18 Minimum CAS latency time, tAAmin In multiples of MTB; e.g., 1280/8 ns.
25 0x19 Minimum RAS to CAS delay time, tRCDmin In multiples of MTB; e.g., 60/8 ns.
26 0x1a Minimum row precharge delay time, tRPmin In multiples of MTB; e.g., 60/8 ns.
27 0x1b Upper nibbles for tRASmin and tRCmin
28 0x1c Minimum active to precharge delay time, tRASmin least significant byte In multiples of MTB
29 0x1d Minimum active to active/refresh delay time, tRCmin least significant byte In multiples of MTB
30 0x1e Minimum refresh recovery delay time, tRFC1min least significant byte In multiples of MTB
31 0x1f Minimum refresh recovery delay time, tRFC1min most significant byte In multiples of MTB
32 0x20 Minimum refresh recovery delay time, tRFC2min least significant byte In multiples of MTB
33 0x21 Minimum refresh recovery delay time, tRFC2min most significant byte In multiples of MTB
34 0x22 Minimum refresh recovery delay time, tRFC4min least significant byte In multiples of MTB
35 0x23 Minimum refresh recovery delay time, tRFC4min most significant byte In multiples of MTB
36 0x24 Reserved tFAWmin most significant nibble
37 0x25 Minimum four activate window delay time, tFAWmin least significant byte In multiples of MTB
38 0x26 Minimum activate to activate delay time, tRRD_Smin, different bank group In multiples of MTB
39 0x27 Minimum activate to activate delay time, tRRD_Lmin, same bank group In multiples of MTB
40 0x28 Minimum CAS to CAS delay time, tCCD_Lmin, same bank group In multiples of MTB
41 0x29 Upper nibble for tWRmin
42 0x2a Minimum write recovery time, tWRmin In multiples of MTB
43 0x2b Upper nibbles for tWTRmin
44 0x2c Minimum write to read time, tWTR_Smin, different bank group In multiples of MTB
45 0x2d Minimum write to read time, tWTR_Lmin, same bank group In multiples of MTB
49–59 0x2e–0x3b Reserved Base configuration section
60–77 0x3c–0x4d Connector to SDRAM bit mapping
78–116 0x4e–0x74 Reserved Base configuration section
117 0x75 Fine offset for minimum CAS to CAS delay time, tCCD_Lmin, same bank Two's complement multiplier for FTB units
118 0x76 Fine offset for minimum activate to activate delay time, tRRD_Lmin, same bank group Two's complement multiplier for FTB units
119 0x77 Fine offset for minimum activate to activate delay time, tRRD_Smin, different bank group Two's complement multiplier for FTB units
120 0x78 Fine offset for minimum active to active/refresh delay time, tRCmin Two's complement multiplier for FTB units
121 0x79 Fine offset for minimum row precharge delay time, tRPmin Two's complement multiplier for FTB units
122 0x7a Fine offset for minimum RAS to CAS delay time, tRCDmin Two's complement multiplier for FTB units
123 0x7b Fine offset for minimum CAS latency time, tAAmin Two's complement multiplier for FTB units
124 0x7c Fine offset for SDRAM maximum cycle time, tCKAVGmax Two's complement multiplier for FTB units
125 0x7d Fine offset for SDRAM minimum cycle time, tCKAVGmin Two's complement multiplier for FTB units
126 0x7e Cyclic rendundancy code (CRC) for base config section, least significant byte CRC16 algorithm
127 0x7f Cyclic rendundancy code (CRC) for base config section, most significant byte CRC16 algorithm
128–191 0x80–0xbf Module-specific section Dependent upon memory module family (UDIMM, RDIMM, LRDIMM)
192–255 0xc0–0xff Hybrid memory architecture specific parameters
256–319 0x100–0x13f Extended function parameter block
320–321 0x140–0x141 Module manufacturer See JEP-106
322 0x142 Module manufacturing location Manufacturer-defined manufacturing location code
323 0x143 Module manufacturing year Represented in Binary Coded Decimal (BCD)
324 0x144 Module manufacturing week Represented in Binary Coded Decimal (BCD)
325–328 0x145–0x148 Module serial number Manufacturer-defined format for a unique serial number across part numbers
329–348 0x149–0x15c Module part number ASCII part number, unused digits should be set to 0x20
349 0x15d Module revision code Manufacturer-defined revision code
350–351 0x15e–0x15f DRAM manufacturer ID code See JEP-106
352 0x160 DRAM stepping Manufacturer-defined stepping or 0xFF if not used
353–381 0x161–0x17d Manufacturer's specific data
382–383 0x17e–0x17f Reserved

DDR5 SDRAM

[edit]

Preliminary table for DDR5, based on JESD400-5 specification.[17]

DDR5 expands the SPD table to 1024-byte. SPD of DDR5 is using the I3C bus.

SPD contents for DDR5 SDRAM
Byte Bit Notes
Dec Hex 7 6 5 4 3 2 1 0
0 0x00 Number of bytes in SPD device
1 0x01 SPD revision for base configuration parameters
2 0x02 Key byte / host bus command protocol type
3 0x03 Key byte / module type
4 0x04 First SDRAM density and package
5 0x05 First SDRAM addressing
6 0x06 First SDRAM I/O width
7 0x07 First SDRAM bank groups & banks per bank group
8 0x08 Second SDRAM density and package
9 0x09 Second SDRAM addressing
10 0x0a Second SDRAM I/O width
11 0x0b Second SDRAM bank groups & banks per bank group
12 0x0c SDRAM optional features
13 0x0d Thermal and refresh options
14 0x0e Reserved
15 0x0f Reserved
16 0x10 SDRAM nominal voltage, VDD

Extensions

[edit]

The JEDEC standard only specifies some of the SPD bytes. The truly critical data fits into the first 64 bytes,[8][9][18][19][20] while some of the remainder is earmarked for manufacturer identification. However, a 256-byte EEPROM is generally provided. A number of uses have been made of the remaining space.

Enhanced Performance Profiles (EPP)

[edit]

Memory generally comes with conservative timing recommendations in the SPD ROM, to ensure basic functionality on all systems. Enthusiasts often spend considerable time manually adjusting the memory timings for higher speed.

Enhanced Performance Profiles is an extension of SPD, developed by Nvidia and Corsair, which includes additional information for higher-performance operation of DDR2 SDRAM, including supply voltages and command timing information not included in the JEDEC SPD spec. The EPP information is stored in the same EEPROM, but in bytes 99–127, which are unused by standard DDR2 SPD.[21]

EPP SPD ROM usage
Bytes Size Full profiles Abbreviated profiles
99–103 5 EPP header
104–109 6 Profile FP1 Profile AP1
110–115 6 Profile AP2
116–121 6 Profile FP2 Profile AP3
122–127 6 Profile AP4

The parameters are particularly designed to fit the memory controller on the nForce 5, nForce 6 and nForce 7 chipsets. Nvidia encourages support for EPP in the BIOS for its high-end motherboard chipsets. This is intended to provide "one-click overclocking" to get better performance with minimal effort.

Nvidia's name for EPP memory that has been qualified for performance and stability is "SLI-ready memory".[22] The term "SLI-ready-memory" has caused some confusion, as it has nothing to do with SLI video. One can use EPP/SLI memory with a single video card (even a non-Nvidia card), and one can run a multi-card SLI video setup without EPP/SLI memory.

An extended version, EPP 2.0, supports DDR3 memory as well.[23]

Intel Extreme Memory Profile (XMP)

[edit]

A similar, Intel-developed JEDEC SPD extension was developed for DDR3 SDRAM DIMMs, later used in DDR4 SDRAM as well. XMP uses bytes 176–255, which are unallocated by JEDEC, to encode higher-performance memory timings.[24]

Later, AMD developed AMP, an equivalent technology to XMP, for use in its "Radeon Memory" line of memory modules optimized for use in AMD platforms.[25][26] Furthermore, motherboard developers implemented their own technologies to allow their AMD-based motherboards to read XMP profiles: MSI offers A-XMP,[27] ASUS has DOCP (Direct Over Clock Profile), and Gigabyte has EOCP (Extended Over Clock Profile).[28]

XMP SPD ROM usage[29]
DDR3 Bytes Size Use
176–184 10 XMP header
185–219 33 XMP profile 1 ("enthusiast" settings)
220–254 36 XMP profile 2 ("extreme" settings)

The header contains the following data. Most importantly, it contains a "medium timebase" value MTB, as a rational number of nanoseconds (common values are 1/8, 1/12 and 1/16 ns). Many other later timing values are expressed as an integer number of MTB units.

Also included in the header is the number of DIMMs per memory channel that the profile is designed to support; including more DIMMs may not work well.

XMP Header bytes[29]
DDR3 Byte Bits Use
176 7:0 XMP magic number byte 1 0x0C
177 7:0 XMP magic number byte 2 0x4A
178 0 Profile 1 enabled (if 0, disabled)
1 Profile 2 enabled
3:2 Profile 1 DIMMs per channel (1–4 encoded as 0–3)
5:4 Profile 2 DIMMs per channel
7:6 Reserved
179 3:0 XMP minor version number (x.0 or x.1)
7:4 XMP major version number (0.x or 1.x)
180 7:0 Medium timebase dividend for profile 1
181 7:0 Medium timebase divisor for profile 1 (MTB = dividend/divisor ns)
182 7:0 Medium timebase dividend for profile 2 (e.g. 8)
183 7:0 Medium timebase divisor for profile 2 (e.g. 1, giving MTB = 1/8 ns)
184 7:0 Reserved
XMP profile bytes[29]
DDR3 Byte 1 DDR3 Byte 2 Bits Use
185 220 0 Module Vdd voltage twentieths (0.00 or 0.05)
4:1 Module Vdd voltage tenths (0.0–0.9)
6:5 Module Vdd voltage units (0–2)
7 Reserved
186 221 7:0 Minimum SDRAM clock period tCKmin (MTB units)
187 222 7:0 Minimum CAS latency time tAAmin (MTB units)
188 223 7:0 CAS latencies supported (bitmap, 4–11 encoded as bits 0–7)
189 224 6:0 CAS latencies supported (bitmap, 12–18 encoded as bits 0–6)
7 Reserved
190 225 7:0 Minimum CAS write latency time tCWLmin (MTB units)
191 226 7:0 Minimum row precharge delay time tRPmin (MTB units)
192 227 7:0 Minimum RAS to CAS delay time tRCDmin (MTB units)
193 228 7:0 Minimum write recovery time tWRmin (MTB units)
194 229 3:0 tRASmin upper nibble (bits 11:8)
7:4 tRCmin upper nibble (bits 11:8)
195 230 7:0 Minimum active to precharge delay time tRASmin bits 7:0 (MTB units)
196 231 7:0 Minimum active to active/refresh delay time tRCmin bits 7:0 (MTB units)
197 232 7:0 Maximum average refresh interval tREFI lsbyte (MTB units)
198 233 7:0 Maximum average refresh interval tREFI msbyte (MTB units)
199 234 7:0 Minimum refresh recovery delay time tRFCmin lsbyte (MTB units)
200 235 7:0 Minimum refresh recovery delay time tRFCmin msbyte (MTB units)
201 236 7:0 Minimum internal read to precharge command delay time tRTPmin (MTB units)
202 237 7:0 Minimum row active to row active delay time tRRDmin (MTB units)
203 238 3:0 tFAWmin upper nibble (bits 11:8)
7:4 Reserved
204 239 7:0 Minimum four activate window delay time tFAWmin bits 7:0 (MTB units)
205 240 7:0 Minimum internal write to read command delay time tWTRmin (MTB units)
206 241 2:0 Write to read command turnaround time adjustment (0–7 clock cycles)
3 Write to read command turnaround adjustment sign (0=pull-in, 1=push-out)
6:4 Read to write command turnaround time adjustment (0–7 clock cycles)
7 Read to write command turnaround adjustment sign (0=pull-in, 1=push-out)
207 242 2:0 Back-to-back command turnaround time adjustment (0–7 clock cycles)
3 Back-to-back turnaround adjustment sign (0=pull-in, 1=push-out)
7:4 Reserved
208 243 7:0 System CMD rate mode. 0=JTAG default, otherwise in peculiar units of MTB × tCK/ns.
E.g. if MTB is 1/8 ns, then this is in units of 1/8 clock cycle.
209 244 7:0 SDRAM auto self refresh performance.
Standard version 1.1 says documentation is TBD.
210–218 245–253 7:0 Reserved
219 254 7:0 Reserved, vendor-specific personality code.

All data above are for DDR3 (XMP 1.1); DDR4 specs are not yet available.

AMD Extended Profiles for Overclocking (EXPO)

[edit]

AMD's Extended Profiles for Overclocking (EXPO) is a JEDEC SPD extension developed for DDR5 DIMMs to apply a one-click automatic overclocking profile to system memory.[30][31] AMD EXPO-certified DIMMs include optimised timings that optimise the performance of its Zen 4 processors.[32] Unlike Intel's closed standard XMP, the EXPO standard is open and royalty-free.[31] It can be used on Intel platforms.[31] At launch in September 2022, there are 15 partner RAM kits with EXPO-certification available reaching up to 6400 MT/s.[33]

Vendor-specific memory

[edit]

A common misuse is to write information to certain memory regions to bind vendor-specific memory modules to a specific system. Fujitsu Technology Solutions is known to do this. Adding different memory module to the system usually results in a refusal or other counter-measures (like pressing F1 on every boot). 

02 0E 00 01-00 00 00 EF-02 03 19 4D-BC 47 C3 46 ...........M.G.F
53 43 00 04-EF 4F 8D 1F-00 01 70 00-01 03 C1 CF SC...O....p.....

This is the output of a 512 MB memory module from Micron Technologies, branded for Fujitsu-Siemens Computers, note the "FSC" string. The system BIOS rejects memory modules that don't have this information starting at offset 128h.

Some Packard Bell AMD laptops also use this method, in this case the symptoms can vary but it can lead to a flashing cursor rather than a beep pattern. Incidentally this can also be a symptom of BIOS corruption as well.[34] Though upgrading a 2 GB to a 4 GB can also lead to issues.

Reading and writing SPD information

[edit]

Memory module manufacturers write the SPD information to the EEPROM on the module. Motherboard BIOSes read the SPD information to configure the memory controller. There exist several programs that are able to read and modify SPD information on most, but not all motherboard chipsets.

  • dmidecode program that can decode information about memory (and other things) and runs on Linux, FreeBSD, NetBSD, OpenBSD, BeOS, Cygwin and Solaris. dmidecode does not access SPD information directly; it reports the SMBIOS data about the memory.[35] This information may be limited or incorrect.
  • On Linux systems and FreeBSD, the user space program decode-dimms provided by i2c-tools decodes and prints information on any memory with SPD information in the computer.[36][37] It requires SMBus controller support in the kernel, the EEPROM kernel driver, and also that the SPD EEPROMs are connected to the SMBus. On older Linux distributions, decode-dimms.pl was available as part of lm_sensors.
  • OpenBSD has included a driver (spdmem(4)) since version 4.3 to provide information about memory modules. The driver was ported from NetBSD, where it is available since release 5.0.
  • Coreboot reads and uses SPD information to initialize all memory controllers in a computer with timing, size and other properties.
  • Windows systems use programs like HWiNFO,[38] CPU-Z and Speccy, which can read and display DRAM module information from SPD.

Chipset-independent reading and writing of SPD information is done by accessing the memory's EEPROM directly with eeprom programmer hardware and software.

A not so common use for old laptops is as generic SMBus readers, as the internal EEPROM on the module can be disabled once the BIOS has read it so the bus is essentially available for use. The method used is to pull low the A0,A1 lines so the internal memory shuts down, allowing the external device to access the SMBus. Once this is done, a custom Linux build or DOS application can then access the external device. A common use is recovering data from LCD panel memory chips to retrofit a generic panel into a proprietary laptop. On some chips it is also a good idea to separate write protect lines so that the onboard chips do not get wiped during reprogramming. A related technique is rewriting the chip on webcams often included with many laptops as the bus speed is substantially higher and can even be modified so that 25x compatible chips can be read back for later cloning of the uEFI in the event of a chip failure.

This unfortunately only works on DDR3 and below, as DDR4 uses different security and can usually only be read. Its possible to use a tool like SPDTool or similar and replace the chip with one that has its WP line free so it can be altered in situ. On some chipsets the message "Incompatible SMBus driver?" may be seen so read is also prevented.

RGB LED control

[edit]

Some memory modules (especially on Gaming PCs)[39] support RGB LEDs that are controlled by proprietary SMBus commands. This allows LED color control without additional connectors and cables. Kernel drivers from multiple manufacturers required to control the lights have been exploited to gain access ranging from full kernel memory access, to MSR and I/O port control numerous times in 2020 alone.[40][41][42]

On older equipment

[edit]

Some older equipment require the use of SIMMs with parallel presence detect (more commonly called simply presence detect or PD). Some of this equipment uses non-standard PD coding, IBM computers and Hewlett-Packard LaserJet and other printers in particular.

See also

[edit]

References

[edit]
  1. ^ Thomas P. Koenig; Nathan John (3 February 1997), "Serial Presence Detection poised for limelight", Electronic News, 43 (2153)
  2. ^ JEDEC Standard 21-C section 4.1.4 "Definition of the TSE2002av Serial Presence Detect (SPD) EEPROM with Temperature Sensor (TS) for Memory Module Applications"
  3. ^ "TN-04-42: Memory Module Serial Presence-Detect Write Protection" (PDF). Micron.
  4. ^ Dean Kent (24 October 1998). "Ram Guide". Tom's Hardware.
  5. ^ Shimpi, Anand Lal. "PC100 SDRAM: An Introduction". www.anandtech.com.
  6. ^ Application note INN-8668-APN3: SDRAM SPD Data Standards, memorytesters.com
  7. ^ PC SDRAM Serial Presence Detect (SPD) Specification (PDF), 1.2A, December 1997, p. 28
  8. ^ a b JEDEC Standard 21-C section 4.1.2.4 "SPDs for DDR SDRAM"
  9. ^ a b JEDEC Standard 21-C section 4.1.2.10 "Specific SPDs for DDR2 SDRAM"
  10. ^ "Understanding DDR3 Serial Presence Detect (SPD) Table".
  11. ^ JESD21-C Annex K: Serial Presence Detect for DDR3 SDRAM Modules, Release 4, SPD Revision 1.1
  12. ^ JESD21-C Annex K: Serial Presence Detect for DDR3 SDRAM Modules, Release 6, SPD Revision 1.3
  13. ^ Delvare, Jean. "[PATCH] eeprom: New ee1004 driver for DDR4 memory". LKML. Retrieved 7 November 2019.
  14. ^ a b JEDEC. "Annex L: Serial Presence Detect (SPD) for DDR4 SDRAM Modules" (PDF).
  15. ^ JEDEC. "EE1004 and TSE2004 Device Specification (Draft)" (PDF). Retrieved 7 November 2019.
  16. ^ JESD21-C Annex L: Serial Presence Detect for DDR4 SDRAM Modules, Release 5
  17. ^ "JESD400-5B(JESD400-5B)". jedec. 2023. Retrieved 31 December 2023.
  18. ^ JEDEC Standard 21-C section 4.1.2.11 "Serial Presence Detect (SPD) for DDR3 SDRAM Modules"
  19. ^ JEDEC Standard 21-C section 4.1.2 "SERIAL PRESENCE DETECT STANDARD, General Standard"
  20. ^ JEDEC Standard 21-C section 4.1.2.5 "Specific PDs for Synchronous DRAM (SDRAM)"
  21. ^ DDR2 UDIMM Enhanced Performance Profiles Design Specification (PDF), Nvidia, 12 May 2006, retrieved 5 May 2009
  22. ^ http://www.nvidia.com/docs/CP/45121/sli_memory.pdf [bare URL PDF]
  23. ^ Enhanced Performance Profiles 2.0 (pp. 2–3)
  24. ^ "What Is Intel Extreme Memory Profile (Intel XMP)?". Intel. Retrieved 26 September 2022.
  25. ^ "Memory Profile Technology - AMP up your RAM". AMD. 2012. Retrieved 8 January 2018.
  26. ^ Martin, Ryan (23 July 2012). "AMD introduces its XMP-equivalent AMP - eTeknix". eTeknix. Retrieved 8 January 2018.
  27. ^ "MSI is worlds first brand to enable A-XMP on Ryzen for best DDR4 performance, launches new models". MSI. 21 March 2017. Retrieved 8 January 2018.
  28. ^ Tradesman1 (26 August 2016). "What does XMP, DOCP, EOCP mean - Solved - Memory". Tom's Hardware Forums. Retrieved 8 January 2018.{{cite web}}: CS1 maint: numeric names: authors list (link)
  29. ^ a b c "Intel Extreme Memory Profile (XMP) Specification, Rev 1.1" (PDF). Intel. October 2007. Archived from the original (PDF) on 6 March 2012. Retrieved 25 May 2010.
  30. ^ "AMD Extended Profiles for Overclocking". AMD. Retrieved 26 September 2022.
  31. ^ a b c Roach, Jacob (6 September 2022). "What is AMD EXPO and should my DDR5 have it?". Digital Trends. Retrieved 26 September 2022.
  32. ^ Bonshor, Gavin (30 August 2022). "AMD EXPO Memory Technology: One Click Overclocking Profiles For Ryzen 7000". AnandTech. Retrieved 26 September 2022.
  33. ^ "AMD announces EXPO technology for DDR5 memory overclocking". VideoCardz. 30 August 2022. Retrieved 26 September 2022.
  34. ^ "Packard Bell LJ65 RAM upgrade". Tom's Hardware Forum. 9 January 2014.
  35. ^ "dmidecode: What's it good for?". Linux.com | The source for Linux information. 29 November 2004.
  36. ^ "decode-dimms(1)". Debian Manpage. Retrieved 16 December 2020.
  37. ^ "decode-dimms". www.freebsd.org. Retrieved 24 January 2021.
  38. ^ "HWiNFO - Professional System Information and Diagnostics". HWiNFO.
  39. ^ "VENGEANCE RGB PRO series DDR4 memory | Desktop Memory | CORSAIR". www.corsair.com. Retrieved 26 November 2020.
  40. ^ ActiveCyber. Viper RGB Driver Local Privilege Escalation (Technical report). CVE-2019-18845 – via MITRE Corporation.
  41. ^ ActiveCyber. CORSAIR iCUE Driver Local Privilege Escalation (CVE-2020-8808) (Technical report). CVE-2020-8808 – via MITRE Corporation.
  42. ^ ActiveCyber. ACTIVE-2020-003: Trident Z Lighting Control Driver Local Privilege Escalation (Technical report). CVE-2020-12446 – via MITRE Corporation.
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