RAM
'RAM' used to be the common name for DRAM: Dynamic Random Access Memory. A memory chip that stores information as electrical charges in capacitors. Plug-in modules (DIMM's= dual in-line memory module) with ever increasing size (32, 64, 128, 512 Mbyte); communicate through the Memory Bus, Northbridge chip and Front-Side-Bus with the main chipset. Originally a-synchronous, now synchronous versions prevails. Clockspeed in state-of-the-art PCs is up to 533 MHz.
SDRAM or SDR-DRAM
Single-Data-Rate DRAM with clock speeds between 66 and 133 MHz (PC66-, PC100- and PC133-SDRAMS), introduced by Intel 1996/'97
RDRAM or DirectRambus-DRAM
Faster SDRAM version (PC800 +, Intel 1999). Modules are called RIMMs (Rambus In-line Memory Modules). Presently mainly used in high-end-desktops ('workstations').
DDR-DRAM or Double-data-rate DRAM
Standard defined by JEDEC ('Joint Electronic Devices Engineering Council'. Features double data transfer channels to the FSB to increase transfer speed (only 'works' with a double data rate also for the FSB). Speed champion in March 2002 is DDR-DRAM Pentium 4 with a Quad-Pumped-Bus, working at 100 MHz clock speed (FSB400) transferring 3,2 Gbyte/s.
Mid 2002 a FSB533 is expected to deliver 4,3 Gbyte/s at 133 MHz. These rates are for standard DIMMs (plug-in) used as main storage for the CPU; for DDR-DRAMs integrated in the PCB of e.g. video cards clockspeeds up to 333 MHz and data transfer speeds up to 10.7 Gbyte/s are theoretically possible. Maximum capacity realised today (March 2002) is 1 Gbyte in Intel's i845 chipset (2GB theoretically feasible with the i845).
Less current types
EDRAM (Enhanced DRAM), ESDRAM, HSDRAM: DRAM types by US-manufacturer Ramtron and its daughter Enhanced .
VCM or VC-SDRAM: Virtual Channel Memory Static DRAM. NEC development with DRAM featuring integrated SRAM.
Future types
DDR333/PC2700, DDR-II, DDR-III: future DRAM concepts being developed by JEDEC.
Courtesy of the French Energy Agency ADEME, Future Electronics project.
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