Talk:Serial presence detect

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Key values include[edit]

  • Memory type (i.e. DDR, SDR, etc)
  • Number of banks
  • Data width (64 or 72 bits)
  • Voltage interface
  • RAM cycle time
  • ECC/non-ECC
  • CAS latencies supported
  • RAS precharge
  • RAS to CAS delay
  • Module bank density
  • Manufacturer JEDEC ID code (Corsair's is 7F 7F 9E 00 00 00 00)
  • Manufacturing location
  • Module part number


russian articles[edit] —Preceding unsigned comment added by (talk) 19:04, 6 November 2007 (UTC)

Parallel Presence Detect notes[edit]

(Some chicken scratches to be turned into an article at some point)

Usually called just presence detect, this used some spare pins on 72-pin SIMMs. They were either open-circuit (pulled high by motherboard resistors) or shorted to ground. All pins open meant "no SIMM inserted" References:

Pins assigned as follows:

  • The first 4 bits on pins 67–70 encode the size and speed.
  • Pin 72 is the ground pin generally connected to.
  • Pin 48 grounded marks an ECC SIMM. Open marks non-ECC. Parity is unclear.
  • Pin 11 is PS5, for extension

Pins 67-70:

PPD decode table
PD4 (70) PD3 (69) PD2 (68) PD1 (67) PD5 (11)
GND GND open 100 ns
GND open 80 ns
open GND 70 ns
open open 60 ns
GND open GND 32 MB
open GND GND 16 MB
open open GND  ???
GND GND open 4 MB
GND open open 2 MB
open GND open 1 MB
open open open 8 MB

Pin 11 mostly changes the capacity, but also causes the 100 ns speed grade to be re-interpreted. This is the JEDEC encoding, apparently IBM and others made up their own. (talk) 15:57, 7 May 2009 (UTC)

SPD information readers[edit]

This section listing various software is very helpful. However, when working with memory, there is a common need to read SPD data without installing an OS -- the memory may not be reliable, it may not be configured correctly, etc. Are there DOS/freeDOS SPD readers? Do any Linux LiveCD distros come with an SPD reader? What would be a good way to make a minimal bootable USB flash drive with SPD read-out function?

Memtest86/86+ has an SPD reading function, but it doesn't work very well (yet)... What the world needs is a good SPD reader that is self-contained bootable like Memtest86, can be put on floppy, can be a boot-time option on CDs, etc. - (talk) 15:28, 27 May 2009 (UTC)

Programs such as CPU-Z allow saving a hex copy of the SPD data. Memtest86 also provides access to the raw hex. But CPU-Z goes a little too far in interpreting and dumbing-down the data. Memtest86 provides no interpretation. (System Speed Test 4.78 does an interesting job of interpretation, and allows access to SPD from DOS, very handy.) Are there any tools (online, javascript, or local) for intpreting such blocks of SPD data, showing the hex as an interpreted data structure? - (talk) 20:50, 15 July 2009 (UTC)

DIMM_ID 2001 from Vanguard Microelectronics Limited is a free DOS program that can also access at least SDRAM SPD data.

The Perl program Memory Serial Presence Detect Decoder by Philip Edelbrock et al. seems to be the most current tool for translating raw SPD hex to human terms. Where is the documentation for this program? - (talk) 02:23, 16 July 2009 (UTC)

Here is the current source: Perl program - (talk) 15:11, 16 July 2009 (UTC)
Downloading the "Original Format" at the bottom of the page is weird, gets an old version without hexdump options. Downloading the "Plain Text" at the bottom of the page seems to work well, giving a very current version, just like that shown on the webpage. It is also possible to download archived distribution tarballs that contain somewhat older versions that still have hexdump options. Reading the source file is full of great details about how to interpret the SPD data.
It is not at all easy to find out how to use/invoke the program; this is all there is:
           "  -c, --checksum          Decode completely even if checksum fails\n",
                "  -x,                     Read data from hexdump files\n",
                "  -X,                     Same as -x except treat multibyte hex\n",
                "                          data as little endian\n",
                "  -h, --help              Display this usage summary\n";
- (talk) 16:12, 16 July 2009 (UTC)

System Speed Test 32 Ver 4.78 is a free DOS program by Vladimir Afanasiev (included in UBCD since version 2.1 2004) that is able to access and display some SPD data. It can also make a report file containing more detailed SPD data. The program can be put on a FreeDOS bootable floppy disk and run directly. - (talk) 13:05, 18 July 2009 (UTC)

What Linux LiveCD distros include lm_sensors and i2c-tools? - (talk) 13:16, 18 July 2009 (UTC)

SPD information writers[edit]

What hardware and software would allow ordinary mortals to change the SPD info?

What equipment is used commercially to write and read SPD parameters? - (talk) 23:27, 27 May 2009 (UTC)

SPDTool can be used to modify the contents of the SPD EEPROM on memory modules.
SPDTool works on all 32-bit and 64-bit versions of Windows 2000/XP/2003/Vista. - (talk) 02:34, 1 July 2009 (UTC)


Please add laptop SPD So-DIMM info. - (talk) 02:24, 28 May 2009 (UTC)

SDRAM and DDR3 parameter tables[edit]

The detailed DDR1 AND DDR2 parameter tables in the article are very useful -- but we need SDRAM and DDR3 parameter tables also, or good annotation of the existing tables clearly stating what is the same and what is different. - (talk) 02:27, 16 July 2009 (UTC)

DDR4 SPD Table[edit]

Does anyone have the time/expertise to add a DDR4 SPD table? (talk) 11:10, 3 May 2017 (UTC)

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