Article Number: 000148441
Random access memory (RAM) is the computer memory that stores information a program needs while it runs. Random-access memory refers to data storage that allows the stored data to be accessed in any order that is, at random, not just in sequence. In contrast, other types of memory devices (such as magnetic tapes, disks, and drums) can access data on the storage medium only in a predetermined order due to constraints in their mechanical design.
Adding memory is one of the easiest, most cost effective ways to boost your computer's performance because most computers are shipped with a minimal amount of memory.
SIMMs (Single Inline Memory Modules) are an older packaging style for RAM. SIMMS are the first memory sticks that were mass produced (Figure 1).
Before SIMMs, most memory was installed directly on the motherboard and there was not much room for upgrade. Different types of SIMMs include: non-parity, parity, fast page and EDO.
The speed for SIMMs is measured in nanoseconds (abbreviated 'ns' or 'nsec'), usually 15ns or less. Check your system documentation to determine RAM specifications for your system.
DIMMs (Dual Inline Memory Module) were the next major improvement in memory technology after SIMM. DIMMs feature 168 pins and offer 64-bit of bandwidth, eliminating the need for installing SIMM memory in pairs for Pentium systems. (Figure 1) DIMMs are 5.375" long and 1.5" high with 8 - 16 of the smaller TSOP (thin, small outline package) chips.
DIMM later evolved to become SDRAM (Synchronous DRAM), which was a derivative of Synchronous Graphics RAM (SGRAM), a very fast but expensive type of video card memory. SDRAM comes in ECC and non-ECC format. ECC memory is similar to parity in that it checks for and traps memory errors. ECC has the added capability of fixing small errors, allowing the system to continue, whereas parity memory halts the system as soon as an error is discovered.Speed
SDRAM was synchronized to the bus speed of the system's FSB (front-side bus), causing a 25% leap in performance. The speed is measured by frequency in megahertz (MHz). SDRAM is generally manufactured as PC100 or PC133 (100MHz and 133MHz, respectively). It is not a good idea to mix PC100 and PC133 SDRAM. Check your system documentation to determine the specifications for your system.
RIMMs (Rambus Inline Memory Module) briefly became the memory of choice on high-end systems in early 2000 (Figure 1).
There are two types of Rambus systems. Initially, systems shipped with a single-channel setup. Subsequent systems use a dual-channel configuration which is better optimized for faster performance. On dual channel systems, two identical RIMMs per channel bank are required for best performance, but the systems will work with single or mixed configurations at reduced performance. RDRAM also comes in ECC and non-ECC format.
Unlike SDRAM, RDRAM operates on a serial circuit, meaning that all memory slots have to be populated for the circuit to close and the memory to be accessible. If only one RIMM is used, then the other slot(s) have to be populated with a CRIMM (Continuity Rambus Inline Memory Module), which is just a module with no memory (Figure 2).
RDRAM speed is measured in megahertz, and Rambus is named according to the speed. Thus, PC800 RDRAM runs at 800MHz. As with SDRAM, it is not a good idea to mix speeds of RDRAM.
DDR SDRAM (Double Data Rate SDRAM) is virtually the most advanced memory technology currently available (Figure 1). Like SDRAM, DDR was born out of the rapid advancements in graphics architecture, introduced with NVIDIA's first GeForce256 video card.
Unlike SDRAM, which performed its read/write functions on the rise of each system clock, DDR memory performs its read/write functions on both the rising and falling edge of each system clock, effectively doubling the memory performance for another huge leap in overall performance.Speed
The speed is measured in megahertz (MHz). DDR-DSRAM is available in a growing number of speeds ranging from, 100 MHz or PC1600 up to 566 MHz or PC4500 with possibly faster speeds eventually added over time.
For more information about DDR-SDRAM speeds, please refer to Dell Knowledge Base article: "How do I determine the data rate, or speed of a DDR SDRAM memory module? "
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14 Nov 2023