Katana VentraIP

Serial presence detect

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).

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.

dmidecode

On 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.

Linux

OpenBSD has included a driver () since version 4.3 to provide information about memory modules. The driver was ported from NetBSD, where it is available since release 5.0.

spdmem(4)

reads and uses SPD information to initialize all memory controllers in a computer with timing, size and other properties.

Coreboot

systems use programs like HWiNFO,[38] CPU-Z and Speccy, which can read and display DRAM module information from SPD.

Windows

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.

Transducer electronic data sheet

Serial Presence Detect Standard, General Standard

SPD Rev1.0 for DDR SDRAM

SPD Rev1.2 for DDR2 SDRAM

SPD Rev1.3 for DDR2 SDRAM

SPECIALITY DDR2-1066 SDRAM

Linux package

i2c-tools

Archived 19 May 2007 at the Wayback Machine

Instructions on how to use lm-sensors or i2c-tools to read the data

 – explanation of various timing values

Memory Performance: 16GB DDR3-1333 to DDR3-2400 on Ivy Bridge IGP with G.Skill