Almost everything about SPD-EEPROM …
To this day, there are still SDRAM DIMMs operating at 66 MHz frequencies that are not equipped with the SPD-EEPROM chip, which contains the most important time parameters and data on the chips used in the module and their manufacturer. The modules at 66 MHz worked flawlessly, allowing memory expansion by adding DIMM modules from other manufacturers or another type of execution. But at frequencies of 100 MHz and higher, the situation is radically changing.
Anticipating the complexity of the functioning of systems with SDRAM from different manufacturers, as well as to facilitate the installation of SDRAM in the system, Intel has developed a specification for serial EEPROM memory. The presence of EEPROM memory on DIMM modules that meet the PC100 specification is a prerequisite, because It contains the exact characteristics of the memory chips that the BIOS needs for the correct system configuration. When the system starts, the Intel 440 chipset sequentially reads the bytes from the EEPROM to identify the SDRAM module and sets the system parameters so that it works correctly with this type of memory.
All SDRAM modules that operate at a frequency of 100 MHz must be performed according to the technology developed by Intel, which takes into account signal delay, input impedance, input and output capacitance, and track inductance. In systems operating at a frequency of 100 MHz and higher, when expanding the memory, one has to think about the characteristics of the module being added to the system, about the manufacturers of SDRAM chips installed on the module, about the coincidence of the time parameters of the modules, about the location of the SDRAM in the slot 1, 2 system, 3 or 4 (it is rare!). Therefore, the Intel PC100 specification defines the need for the presence of EEPROM on the module and describes in detail all the parameters that must be entered by the DIMM manufacturer in the EEPROM memory.
It must be remembered that there are a lot of manufacturers of SDRAM modules. They are produced by companies that spent a little more than $ 20,000 on the purchase of an installation station, and about 5 thousand on a module shelf life tester. As a rule, such companies do not receive first-class SDRAM chips and, accordingly, the parameters of the finished SDRAM module are not the best. Introducing the PC100 specification, Intel hoped that the need to comply with very stringent technical requirements would reduce the number of manufacturers of SDRAM modules, but the state of the SDRAM PC100 market in Ukraine shows that limiting the circle of manufacturers even for Intel is not so simple.
Many manufacturers simply stick the “PC100” label on their SDRAM modules and sell them as fully complying with the PC100 specification. However, there are ways to convict them of lies, and in this publication we will try to offer you a way to avoid fraud.