DRAM Packages

Physical DRAM Packages Physically, the main memory in a system is a collection of –Chips or –Modules containing chips that are usually plugged into the motherboard. These chips or modules vary in their electrical and physical designs and must be compatible with the system into which they are being installed to function properly.

CPU and Chipset The CPU and motherboard architecture (chipset) dictates a particular computer ’ s physical memory –Capacity, –Speed and –Data bus width requirements that can be installed.

Individual Memory Chips Originally, systems had memory installed via individual chips. They are often referred to as dual inline package (DIP) chips because of their designs. The original IBM XT and AT had 36 sockets on the motherboard for these individual chips, and then more of them were installed on the memory cards plugged into the bus slots.

DIP Packages

Apple-I single board computer

Problems of using DIP Memory Chips Time-consuming, and Labor-intensive way to deal with memory, They crept out of their sockets over time.

Solution The alternative to this at the time was to have the memory soldered into either the motherboard or an expansion card. Made memory troubleshooting difficult.

Module What was necessary was a chip that was both soldered and removable, and that is exactly what was found in the module called a SIMM.

Different types of Module For memory storage, most modern systems have adopted the –SIMM (single inline memory module), –DIMM (dual inline memory module), or –RIMM (Rambus Inline Memory Module) as an alternative to individual memory chips.

Modules These small boards plug into special connectors on a motherboard or memory card. The individual memory chips are soldered to the module, so removing and replacing them is impossible. Instead, you must replace the entire module if any part of it fails. The module is treated as though it were one large memory chip.

SIMM (Single In-line Memory Module) 30-pin SIMM has 8-bit data bus 72-pin SIMM has 32-bit data bus May have several chips (ex: 2, 3, 8, 9)

Bank of Memory A bank of memory must contain the same amount of bits as the data bus of the CPU/System.

Number of Modules make a Memory Bank

A typical 30-pin SIMM Dimensions The one shown here is 9-bit, although the dimensions would be the same for 8-bit.

30-pin and 72-pin SIMM Pictures

A typical 72-pin SIMM

A typical 168-pin SDRAM DIMM

A typical 184-pin DDR DIMM

A typical 184-pin RIMM

SDRAM-DIMM vs. DDR-DIMM vs. RIMM

Characteristics of 168-pin SDRAM DIMM The DIMM uses serial presence detect (SPD). It consists of a small EEPROM or Flash memory chip on the DIMM that contains specially formatted data indicating the DIMM ’ s features. This serial data enables the motherboard to autoconfigure to the exact type of DIMM installed.

Characteristics of 168-pin SDRAM DIMM DIMMs can come in several varieties, including –unbuffered or buffered and –3.3V or 5V. All PC systems use unbuffered DIMMs. DIMM designs for PCs are almost universally 3.3V. If you install a 5V DIMM in a 3.3V socket, it would be damaged, but fortunately, keying in the socket and on the DIMM prevents that.

168-pin DRAM DIMM notch key definitions

RDRAM bus layout showing a RIMM and one continuity module

The markings on a typical memory chip

Installing SIMM Align the module (notch and protrusions in the socket). The notch on this SIMM is shown on the left side. Insert the SIMM at a 45° angle and then tilt it forward until the locking clips snap into place.

Removing SIMM Pull plastic tabs outward Push the top at an angle away from the socket Pull out of the socket

Installing DIMM / RIMM Align the module (notch and protrusions in the socket) Insert at a straight angle (90º) Push until the ejector tab locks into place in the notch on the side of the DIMM.

Removing DIMM / RIMM Push out the ejector tabs and the DIMM will pop out.

72-pin SODIMM (Small Outline DIMMs) 72-pin SODIMMs are typically used in the Pentium-II Laptop computer system

144-pin SODIMM (Small Outline DIMMs) 144- SODIMMs are typically used in the PC66 and PC100 SDRAM Laptop compatible computers

100-pin SODIMM (Small Outline DIMMs) 100- PIN DIMMs are primarily used in printers

144- PIN Micro-DIMMs 144- PIN Micro-DIMMs are primarily used in digital assistants, subnotebooks and notebook computers.

200- Pin DDR-SODIMM