Understanding Computer Memory

Learn About Random Access Memory Technologies

What is computer memory? DRAM: A computer memory chip is actually an integrated circuit (IC), consisting of billions of transistors and capacitors. The transistors act as a switch to transfer data while the capacitors hold this particular data as a static charge (a capacitor has the ability to hold an electrical charge between a dielectric substance). The type of memory we are talking about is called DRAM, or “Dynamic Random Access Memory.” The transistors and capacitors are paired up to form “memory cells” within the chip itself. Dynamic RAM requires constant refreshing of electrical charge by an onboard memory controller, otherwise the data is erased. This is why rebooting your PC will clear all data in memory (helpful when a program causes the system to lock up). The term “random access” refers to being able to locate, read and write data to any memory cell on the RAM chip regardless of where its located, meaning it’s not sequential, such as the older VHS movies which required you to fast forward or rewind to get to a different segment of a video.

The older standards of DRAM modules are long obsolete. They used 30 and 72 pin SIM configurations. SIM means “single inline memory module”, meaning that the memory chips were installed on only one side of the module but not the other. Information is generally processed by fetching instructions (data) from the hard disk, loading these instructions into RAM, and then processing the data stored in RAM from the main system micro-processor. In some cases data is also processed directly from the hard disk drive, this is the case with “virtual memory” and “page files” in operating systems.Older operating systems such as Windows XP relied heavily on virtual memory, since RAM at the time was still in its primitive stages, and was very expensive to produce, as most solid state, flash based storage mediums are. Nontetheless, solid state technology is constnatly being refined, and new and better ways of manufacturing it have brought down its once inconceivable price.

SDRAM:

“Synchronous Dynamic Random Access Memory”, unlike earlier forms of computer memory, SDRAM had the ability to synchronize to the system clock. It had problems though, particularly because of its design. It could only transfer data once per each clock cycle. This was called “single data rate” ram for this very reason. Most of the SDRAM modules consisted of 168-Pin DIMMs. DIMM stands for “Dual Inline Memory Module”, meaning that the memory module itself had memory chips on both sides of the cartridge. SDRAM was always rated by bus speed. If you see markings that state PC133, PC100, etc, just know they are referring to the speed of the system bus. In this case PC133 means 133Mhz, and PC 100 means 100Mhz respectively. This RAM, like its predecessors is long outdated and you will be hard pressed to actually come across it today.

DDR, DDR2, and DDR3, etc:

The original DDR SDRAM used a 184 Pin configuration and was usually measured by its actual speed in MHz, although many times also measured by its theoretical maximum throughput (PC2700). DDR stands for “Double Data Rate” and is also a synchronous form of dynamic random access memory. Unlike SDRAM, DDR transferred data twice for each one full clock cycle, once as the frequency rises, and again as the frequency drops, effectively doubling the data rate of data transmission to and from RAM. This being said, a DDR memory module rated at 200MHz would effectively transfer data at a rate of 400MHz. How? Well, remember, it transfers data twice for each clock cycle! Most get very confused by this. People go out, by RAM, notice that its only running at 200MHz, yet it states 400MHz on the cartridge and packaging itself.

Continue To Part 2 (RAM)