FPM (Fast Page Mode) and EDO (Extended Data Out) technologies are older technologies popular in the late 1980's and early 1990's. These technologies should not be used for new designs, but STEC can still provide many modules using these technologies for older designs that may still be in production or for replacement parts for customer's systems that are installed in the field.

SDRAM (Synchronous DRAM) is the common term to classify PC66 (1997), PC100 (1998) and PC133 SDRAM (1999/2000). SDRAMs are based on standard dynamic RAM chips, but have sophisticated features that make them considerably faster. First, SDRAM chips are fast enough to be synchronized with the CPU's clock, which eliminates wait states. Second, the SDRAM chip is divided into two cell blocks, and data is interleaved between the two so that while a bit in one block is being accessed, the bit in the other is being prepared for access. This allows SDRAM to burst the second and subsequent, contiguous characters at a rate of 10ns, compared to 60ns for the first character. SDRAM chips use a power supply voltage of 3.3 volts.

Double Data Rate (DDR) is an advancement over SDRAM technology that increases memory bandwidth and performance while maintaining competitive pricing. DDR is the evolutionary technology that succeeded the previous standard Synchronous DRAM technology, which is now called SDR (Single Data Rate). DDR achieves its performance by transferring data on both the rising edge and the falling edge of the clock. Standard speeds for DDR include PC-2100 (7.5 ns clock), PC-2700 (6.0 ns clock), and PC-3200 (5.0 ns clock). Chips with DDR technology also save power because they run at 2.5 or 2.6 volts rather than the higher voltages used by the earlier technologies.

DDR2 is an evolutionary enhancement over DDR. This technology is currently the largest selling technology today and offers the best cost per bit. Most new systems designs today would likely choose to use DDR2. It takes advantage of the DDR improvements to transfer data on both edges of the clock. However, it further improves the speeds to provide standard transfer rates of PC2-3200 (5.0 ns clock), PC2-4200 (3.75 ns clock), PC2-5300 (3.0 ns clock), and PC2-6400 (2.5 ns clock). DDR2 chips save further power over the previous technologies because these chips use a standard voltage of 1.8 volts.

DDR3 continues the evolution of the double data rate technologies to provide continued improvements in performance. The DDR3 technology is just being introduced and is not projected to be cost competitive with the DDR2 technology until 2009 or 2010. However, it does offer increased transfer rates of PC3-6400 (2.5 ns clock), PC3-8500 (1.875 ns clock), PC3-10600 (1.5 ns. Clock), and PC3-12800 (1.25 ns clock). So system designs that are performance driven may want to start looking at this technology. DDR3 also saves power by lowering the power supply voltage to 1.5 volts.

In order to ensure that there are no compatibility problems when using STEC DRAM modules with Intel motherboards, STEC will qualify certain modules at CMTL (Computer Memory Test Labs) on certain Intel motherboards. For those customers using those motherboards, this will ensure full compatibility and minimize technical issues. Motherboard Qualified Memory can potentially be any technology type or form factor. These modules do have a fixed bill-of-materials which STEC will not change without first resubmitting the new BOM to CMTL for re-qualification.

The full-sized DIMM form factor was the original form factor that was created for DRAM modules. It is in wide use with desktops, servers, and systems used in embedded and telecommunications applications. This module is 133.5 mm wide and is 30 mm or more tall. Standard full-sized DIMM form factors have been defined with pin counts of 168 (SDRAM), 184 (DDR), and 240 (DDR2 and DDR3).

The Very Low Profile (VLP) DIMM was created to save height for space constrained systems, including blade servers and ATCA (Advanced Telecommunications Architecture) applications. The DIMMS are also 133.5 mm wide and have the same pinout as the DDR, DDR2, and DDR3 full-sized DIMMs. However, these modules will typically have a height between 18-19 mm. This shortened height allows the designer to use a vertical socket and still fit the DIMM into his constrained chassis space.

The So-DIMM is a shortened DIMM form factor that was created originally for use in notebook computers. This module has a width of 67.6 mm and these will typically use a horizontal socket when designed into the system. The original So-DIMM was defined without ECC for use in notebooks. But additional versions that include ECC have been created for embedded, telecomm, and other applications that require additional reliability. The So-DIMM can come in versions with pin-counts of 144 pins (SDRAM), 200 pins (DDR and DDR2), and 204 pins (DDR3).

The mini-DIMM is a relatively new form factor that was invented to provide the benefits of a shortened DIMM length but still provide additional pin-count to support new features in the DDR2 technology. Mini-DIMMs are currently available for only DDR2 in a 244-pin module and will always include ECC. These modules are 82 mm long. It is likely that future extensions to the DDR3 standard will also provide this form factor for DDR3 technologies.

The VLP mini-DIMM is a new form factor that combines the shorter length of the mini-DIMM with the shorter height of the VLP DIMM. This form factor is a good solution for highly space constrained systems that only need a small to moderate amount of memory. The typical size of a VLP mini-DIMM is 82 mm long with a height between 18-19 mm.