Graphics Card Memory

The video memory, often referred to as VRAM, or when discussing graphics cards as simply "RAM," is the amount of local memory available to the graphics card to store images before they are sent to the monitor.

Video memory is most expressed in megabytes or gigabytes of RAM. A "512 meg" graphics card is understood to have 512 Megabytes of Video Memory, while a "1 gig" graphics card has 1 Gigabyte of Video Memory.

The first 3D graphics cards with on-board video memory were released in the early '90s, and had 4 megs of RAM. Today, the fastest commercially available graphics cards can offer up to 6 gigs, or over 1,000 times the amount of the first graphics cards released on the market.

Graphics Card Memory Function

The video RAM is much like a notepad - it's a place where the graphics card can temporarily store information for later use. The types of information that a graphics card stores in the video memory include:

And more. This is why games often take a long time to load - all the textures and light sources must be read from the hard drive into the video memory. Since the hard drive sends and receives information much slower than the video RAM, this process often accompanies the notorious "loading" bar in the center of the screen while the video RAM swaps information in and out.

By pre-loading textures, images, physics calculations, and various other bits of information integral to the image production process, the GPU does not have to access the hard drive or the system memory to find the bits of information it needs to send images to the display adapter; everything it needs it right there inside the graphics card.

In this sense, pre-loading is not only a tremendous timesaver, it is vital to three-dimensional image processing. If there were no video memory to hold all of this information, allowing the GPU quick access, then everything would have to be read from the hard drive, and real-time rendering would be impossible.

Video RAM is also sometimes referred to as the "Frame Buffer," since the job of the video memory is to hold images in place while the Graphics Processing Unit (GPU) performs the calculations.

Types of Video Card Memory

All video memory manufactured today is a specialized form of DRAM (Dynamic Random Access Memory) built with graphics applications in mind. It is dual-ported, meaning data can be read from and written to the RAM at the same time, making it much faster than standard RAM.

EDO-RAM

Initial VRAM variants were based on EDO-RAM, or Extended Data-Out Dynamic Random Access Memory. EDO-RAM does not wait for all of the processing of the first bit before continuing to the next one. As soon as the address of the first bit is located, EDO DRAM begins looking for the next bit, making it faster than previous versions of RAM used for graphics cards.

SDRAM

The advent of SDRAM, or Synchronous Dynamic Random Access Memory, gave birth to the burst mode concept of RAM function, greatly improve performance beyond EDO-RAM. It does this by continuing to scan a row containing the requested bit while moving rapidly through the columns, reading each bit as it goes.

By continuously scanning, any data needed by the CPU or GPU will most likely already be in sequence. SDRAM is commonly used as standard RAM in desktop computers today.

DDR-SDRAM

Double Data Rate Synchronous Dynamic Random Access Memory, usually referred to as simply "DDR," was released in 2000 and upped the ante yet again.

Compared SDRAM, DDR allows higher data transfer rates by more strictly and accurately controlling the timing of the electrical data and clock signals.

DDR utilizes "double pumping," which is a transference of data on both the rising and falling points of the clock signal, and allows the clock signal to be lowered while still increasing overall data flow. Lowering clock frequency increases overall data flow speed in the pathway between the RAM and the RAMDAC.

Double Data Rate refers to the fact that, due to double pumping, DDR SDRAM can achieve twice the bandwidth, and therefore twice the memory transference, of SDRAM at the same frequency.

DDR2 and DDR3

Since 2000, two new iterations of DDR SDRAM have hit the market, each faster and allowing for a larger total RAM pool than previous versions.

It should be noted that DDR2 and DDR3 are not backwards-compatible, meaning that a stick of DDR2 and a stick of DDR3 will not work properly in conjunction with one another.

DDR4

Slated for release in 2015, the newest version of RAM is expected to run at 1.2 V or less, which is, amazingly, actually lower than the 1.5 V charge of DDR3 RAM. In addition, DDR4 will handle in excess of 2 billion data transfers per second, making it the fastest RAM on the planet.