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 faste
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, data bits at a rate of 10ns, compared to 60ns for the first character. SDRAM chips use a power supply voltage of 3.3 volts.
SDRAM chips use a clock which is synchronized with the CPU's clock. 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 acceded, the bit in the other is being prepared for access. This allows the SDRAM to burst the second and subsequent characters at a rate of 10 nsec. (PC-100) or 7.5 nsec. (PC-133).
SDRAM is an older interface technology that has been superseded by DDR, DDR2, or DDR3 in many applications. It may still be the right choice for designs using older microprocessors or chipsets that were designed several years ago. It may also be the right choice for use as an upgrade for systems that have already been installed in the field. You should refer to your system or microprocessor documentation to see if it does use the SDRAM interface. SDRAM modules will not work in DDR or DDR2 sockets or vice-versa so it is important to use exactly the type of module that was originally intended for your application.
DIMMs have several different options for providing signal buffering on the DIMM to improve the performance and allow the system to support more DIMMs in a system. The list below describes the different types of buffering that can be on a DIMM.
The So-DIMM is a shortened DIMM form factor that was created originally for use in notebook computers. This module has a width of 67.6mm 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).
A Registered DIMM has a chip called a Register chip on the DIMM module that will latch and buffer the address lines. Because of this Register chip, the DRAM controller will only see one load for the address lines instead of the 9 or 18 or more loads that would be present if the addresses were routed to every DRAM chips. The lighter loading will allow the DRAM controller to drive more DIMMs and at faster speeds. This type of DIMM module is commonly used in servers where there may be 8 or 16 or more DIMMs in a system. Registered DIMMs are only offered in versions with ECC.
An Unbuffered DIMM has no buffering on the DIMM. The DRAM controller will drive the address lines directly to each chip on the DIMM and the DIMM outputs will be go from the DRAM chip to the DRAM controller. This type of DIMM is commonly used on desktop and laptop PCs where the total amount of memory is limited and only one or two DIMMs are used in a system. Unbuffered DIMMs can be offered in versions without or without ECC.
• Scalability of Speeds to Reach 133 Mhz
• Available in both Unbuffered and ECC Registered Versions
• Available in 168 DIMM and 144 pin So-DIMM Form Factors
• 3.3 Volt Operating Voltage
• High density: Up to 2GB
• Ideal for Legacy Designs and Embedded Systems Designs that use simpler DRAM Controllers
There are two standard speeds for SDRAM products: PC-100 and PC-133.
PC-100 modules operate at a 100MHz clock frequency and achieve a peak bandwidth of 800MB/s.
PC-133 modules operate at a 133 MHz clock frequency and achieve a peak bandwidth of 1066MB/s.
