Types of RAM on your PC
Introduction
The type of RAM doesn't matter nearly as much as how much of it you've got, but using plain old SDRAM memory today will slow you down. There are three main types of RAM: SDRAM, DDR and Rambus DRAM.
SDRAM (Synchronous DRAM)
Almost all systems used to ship with 3.3 volt, 168-pin SDRAM DIMMs. SDRAM is not an extension of older EDO DRAM but a new type of DRAM altogether. SDRAM started out running at 66 MHz, while older fast page mode DRAM and EDO max out at 50 MHz. SDRAM is able to scale to 133 MHz (PC133) officially, and unofficially up to 180MHz or higher. As processors get faster, new generations of memory such as DDR and RDRAM are required to get proper performance.
DDR (Double Data Rate SDRAM)
DDR basically doubles the rate of data transfer of standard SDRAM by transferring data on the up and down tick of a clock cycle. DDR memory operating at 333MHz actually operates at 166MHz * 2 (aka PC333 / PC2700) or 133MHz*2 (PC266 / PC2100). DDR is a 2.5 volt technology that uses 184 pins in its DIMMs. It is incompatible with SDRAM physically, but uses a similar parallel bus, making it easier to implement than RDRAM, which is a different technology.
Rambus DRAM (RDRAM)
Despite its higher price, Intel has given RDRAM its blessing for the consumer market, and it will be the sole choice of memory for Intel's Pentium 4. RDRAM is a serial memory technology that arrived in three flavors, PC600, PC700, and PC800. PC800 RDRAM has double the maximum throughput of old PC100 SDRAM, but a higher latency. RDRAM designs with multiple channels, such as those in Pentium 4 motherboards, are currently at the top of the heap in memory throughput, especially when paired with PC1066 RDRAM memory.
DIMMs vs. RIMMs
DRAM comes in two major form factors: DIMMs and RIMMS.
DIMMs are 64-bit components, but if used in a motherboard with a dual-channel configuration (like with an Nvidia nForce chipset) you must pair them to get maximum performance. So far there aren't many DDR chipset that use dual-channels. Typically, if you want to add 512 MB of DIMM memory to your machine, you just pop in a 512 MB DIMM if you've got an available slot. DIMMs for SDRAM and DDR are different, and not physically compatible. SDRAM DIMMs have 168-pins and run at 3.3 volts, while DDR DIMMs have 184-pins and run at 2.5 volts.
RIMMs use only a 16-bit interface but run at higher speeds than DDR. To get maximum performance, Intel RDRAM chipsets require the use of RIMMs in pairs over a dual-channel 32-bit interface. You have to plan more when upgrading and purchasing RDRAM.
Other Memory Types
- Credit Card Memory: Credit card memory is a proprietary self-contained DRAM memory module that plugs into a special slot for use in notebook computers.
- PCMCIA Memory Card: Another self-contained DRAM module for notebooks, cards of this type are not proprietary and should work with any notebook computer whose system bus matches the memory card's configuration.
- CMOS RAM: CMOS RAM is a term for the small amount of memory used by your computer and some other devices to remember things like hard disk settings.This memory uses a small battery to provide it with the power it needs to maintain the memory contents.
- VRAM: VideoRAM, also known as multiport dynamic random access memory (MPDRAM), is a type of RAM used specifically for video adapters or 3-D accelerators. The "multiport" part comes from the fact that VRAM normally has two independent access ports instead of one, allowing the CPU and graphics processor to access the RAM simultaneously. VRAM is located on the graphics card and comes in a variety of formats, many of which are proprietary. The amount of VRAM is a determining factor in the resolution and color depth of the display. VRAM is also used to hold graphics-specific information such as 3-D geometry data and texture maps. True multiport VRAM tends to be expensive, so today, many graphics cards use SGRAM (synchronous graphics RAM) instead. Performance is nearly the same, but SGRAM is cheaper.
How much RAM?
The amount of RAM memory used in modern desktop and laptop computers is expressed in megabytes (MB) and gigabytes(GB). A gigabyte (1GB) is 1024MB. Most desktop and laptop computers that came with Windows XP preinstalled came with 512MB. However, this increased to gigabytes when Windows Vista was released in January 2007. A computer with Windows Vista preinstalled should have a minimum of 2GB or RAM memory to run comfortably, however, 1GB of RAM memory in computers running a 32-bit version of Windows 7 should suffice, because the 32-bit versions of Windows 7 can run on a comparatively low-spec netbook computer, most of which currently only have 1GB of memory.
32-bit versions of Windows cannot use more than about 3.5GB of memory; 64-bit versions of Windows can support far more memory than most home users require. However, up to 4GB of memory, the 64-bit versions require twice as much memory as the 32-bit versions, so the minimum a 64-bit version should have is 2GB for Windows 7 and 4GB for Windows Vista. Most computers in use currently use a 32-bit version of Windows.
To find out which bit version of Windows you have, in Windows XP go Start => Control Panel and look for System and look on the General tab of the System Properties window. In Windows Vista choose the Classic View in the Control Panel. In Windows 7, just enter the word system in the Start => Search programs and files box to be provided with a clickable link to the System Properties window.
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