These technical notes are provided as a service to our customers.

Above is a 30 PIN SIMM. It has 30 gold pins on the front and the back. It comes in either a one MEG or four Megabyte Strip. Most computers use this in a set of four. Length is 3.5 inches long and the height varies. This is the technology used in the early 1980's.

Animated GIF by Donnie Heath.

Above is a 72 PIN SIMM. It has 72 gold or tin pins on the front and the back. Most mother board manufacturers such as Intel are requesting that you use tin leads to avoid plating. It comes in either a Four 1X, Eight 2X, Sixteen 4X or thirty-two 8X Megabyte Strip. Most 486Based computers can use these one at a time and can use either parity X36 or non parity X32 RAM. Most Pentium based computers use this in a set of two. Pentiums use these in either EDO or non parity X32 arrangements. Length is 4.25 inches long and the height varies. This is the technology used in the early 1990's.

SOJ Video RAM. Known as a 256K X 16 SOJ Can either be EDO or Non EDO check your video card manual to be sure. If you don't know then use non EDO. Length is 1 inch by 7/16ths wide.  These are also used to make most memory strips.  They use SOJ modules of different densities to make SIMM strips and DIMM strips.

SDRAM DESCRIPTION

SDRAM DIMM SyncDRAM , which is another type of PC memory architecture. This provides a significant performance improvement over conventional Fast Page Mode (FPM) or Extended Data Output (EDO). A key difference found in SyncDRAM is that it is synchronized to the system clock signal, which means that all operations run at the same speed as the processor bus, i.e. 60 or 66MHz. Up to 100 and 133 MHz This is compared to conventional memory architectures which run asynchronously to the processor bus. Due to this synchronization, data bits are retrieved faster and thereby increase system performance.

PC applications commonly access DRAM data in 4-quad word (Qword) burst lengths. Optimum system performance is achieved when data is fed to the processor on par with the system clock. Data access from an L2 cache comes close to meeting this requirement as typical only one or two wait states are inserted while accessing the first data. However, the remaining three Qwords are delivered on a par with the processor speed, denoted as a 2/1/1/1 burst rate. When, however, the requested data must come directly from DRAM, the burst rate is degraded. Assuming the burst is from a DRAM page that is already open (page hit), the achievable burst rate at 66MHz using 60ns FPM DRAMs is 5/3/3/3 cycles; for EDO DRAMs it is 6/2/2/2. SyncDRAMs can reduce burst rates to 7/1/1/1 for L2 cache misses. While SyncDRAM takes more time to locate the first data bit, it then is faster at retrieving the next three Qwords. Furthermore, it really excels at back to back reads which assumes a page hit:

SDRAM
Synchronous DRAM (SDRAM) is “in synch” or synchronized to the system clock that controls the CPU. The clock that controls the microprocessor also controls the SDRAM, thus eliminating wait states and reducing data retrieval times. This synchronization allows the memory controller to know on which clock cycle data requests will be available. Data is thus input to the rising edge of the clock instead of with every two clock cycles (like EDO) or every three clock cycles (like FPM). SDRAM also utilizes multiple memory banks that function simultaneously, in addition to a burst mode feature that addresses an entire block rather than just one piece of data. SDRAM is currently in production.

• What is RDRAM* memory?
  Direct Rambus RDRAM memory uses a new technology that increases processor-to-memory bandwidth up to 1.6 GB/sec.

  
  2.5V, 168-pin (64/128 Mbit Non-ECC or 72/144 Mbit ECC), 400 MHz, 356 MHz, and 300 MHz RDRAM RIMM* modules. The devices are known as PC800, PC700, and PC600 respectively.

  Note: There can be no empty RIMM connectors. RIMM connectors without a RIMM installed must be populated with Continuity RIMMs. The Continuity RIMMs are used to provide signal paths for the memory modules.

Registered DIMMs have Control chips along with the 8 OR 9 SOJ chips.  They are located below ase U11 U12 and U13.

What is  SPD?
When a computer system boots up, it needs to “detect” the configuration of the memory modules in order to run properly. SPD (Serial Presence Detect),  uses an EPROM to store information about the module. The SPD then tells the computer what kind of   RAM is installed in the system

The difference between 2-clock and 4-clock RAM.
SDRAM requires clock lines running from the system clock to the memory module. Two clock means there are two clock lines running to the module, and four clock means there are four clock lines running to the module. Four clock designs are faster because they allow less chips per clock line, enabling a quicker interface with data.

PC 100 MHz Bus used on Intels Seattle SE440BX Mother board.

Intel  introduced the PC 100 main memory bus in their system designs in 1995.  PC 100 is a faster main memory bus. At 100MHz, PC 100 is roughly 33% faster than the earlier 66MHz main memory bus. To match this faster 100MHz bus speed, 100MHz SDRAM modules will be the required memory technology for PC 100.  SDRAM speed ranges from PC66 to PC100 to PC133. 

Systems with CPU's from 233 to 333 have a 66 MHz bus. CPU's 350 MHz and above use a 100 MHz bus even number speeds above 500 are usually PC100 and speeds like 733 or 933 are PC133.

Definition: Just what is a Bus?

The bus is the main communication avenue in a PC. The bus is the primary data traffic lane from the CPU to all key subsystems. It consists of various parallel connections  to which the CPU, memory, and all input-output devices are connected. The bus can send data in either direction between any two system devices. For example, a 16-bit bus transfers two bytes at a time over 16 wires, a 32-bit bus transfers four bytes at a time over 32 wires. Much like a highway, more lanes equals greater traffic flow.

  What is DDR?

A dual inline memory module (DIMM) consists of a number of memory components that are attached to a printed circuit board. The gold pins on the bottom of the DIMM provide a connection between the module and a socket on a larger printed circuit board. The pins on the front and back of a DIMM are not connected, providing two lines of communication paths between the module and the system.

184-pin DIMMs are used to provide DDR SDRAM memory for desktop computers. Each 184-pin DIMM provides a 64-bit data path, so they are installed singly in 64-bit systems. 184-pin DIMMs are available in PC1600 DDR SDRAM or PC2100 266 DDR SDRAM or PC2700 known as 333.

The number DDR components on a 184-pin DIMM may vary, but they always have 92 pins on the front and 92 pins on the back for a total of 184. 184-pin DIMMs are approximately 5.375" long and 1.375" high, though the heights may vary. While 184-pin DIMMs and 168-pin DIMMs are approximately the same size, 184-pin DIMMs have only one notch within the row of pins.

A DDR SDRAM DIMM will not fit into a standard SDRAM DIMM socket.

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Some prices may be different than the prices in the Retail store. Quanities may be limited and RAM prices are good only for inventory on hand. You will be notified if there are any problems with your order. We only ship to United States addresses. Not all pictures have been added but we are working on it.

Computer & Software Outlet of Winston-Salem  North Carolina.

A Division of Jemak, Inc Other trade names include Salem Salvage and Surplus.

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Last modified: May 25, 2004