VIDEO RAM

Presented by GHOLAMREZA KAKAMANSHADIPANJAB UNIVERSITY, CHD, INDIA

Nov. 2014

REZA.MANSHADI@GMAIL.COM

Video RAM

• Video adapters rely on their own onboard memory

that they use to store video images while processing

them.

• The AGP specification supports the use of system

memory for 3D textures, this feature is infrequently

supported, now that video cards routinely ship with

32MB, 64MB, or more of onboard memory.

• Many low-cost systems with onboard video use theuniversal memory architecture (UMA) feature to sharethe main system memory. In any case, the memory onthe video card or borrowed from the system performsthe same tasks.

• The amount of memory on the adapter or used byintegrated video determines the maximum screenresolution and color depth the device can support.You often can select how much memory you want on aparticular video adapter; for example, 32MB, 64MB,and 128MB are common choices today.

• Adding more memory is not guaranteed to speed

up your video adapter, it can increase the speed

if it enables a wider bus (from 64 bits wide to

128 bits wide) or provides non display memory

as a cache for commonly displayed objects.

• It also enables the card to generate more colors

and higher resolutions and, for AGP cards allows

3D textures to be stored and processed on the

card, rather than in slower main memory.

Memory Types Used in Video Display Adapters

• VRAM and WRAM are dual-ported memory types

that can read from one port and write data through

the other port.

• This improves performance by reducing wait times

for accessing the video RAM compared to FPM

DRAM and EDO DRAM.

• SGRAM, SDRAM, DDR, and DDR-IISDRAM which are derived from popularmotherboard memory technologies havereplaced VRAM, WRAM, and MDRAM ashigh-speed video RAM solutions.

• Their high speeds and low production costshave enabled even inexpensive video cards tohave 16MB or more of high-speed RAMonboard.

Video RAM Speed

• Video cards with the same type of 3D graphicsprocessor chip (GPU) onboard might use differentspeeds of memory.

• For example, two cards that use the NVIDIA GeForceFX 5200 the Prolink PixelView and the Chaintech A-FX20 use different memory speeds. The Prolink carduses 4ns memory, but the Chaintech card uses 5nsmemory.

• Sometimes, video card makers also match differentmemory speeds with different versions of the samebasic GPU, as with ATI’s Radeon 9800 XT and 9800Pro. The 9800XT has a core clock speed of 412MHz,versus the 9800 Pro’s 380MHz clock speed.

RAM Calculations

• The amount of memory a video adapter needsto display a particular resolution and colordepth is based on a mathematical equation.

• A location must be present in the adapter’smemory array to display every pixel on thescreen, and the resolution determines thenumber of total pixels.

• For example, a screen resolution of1024×768 requires a total of 786,432 pixels.

• If you want to display that resolution with only two colors, you would need only 1 bit of memory space to represent each pixel.

• If the bit has a value of 0, the dot is black, and if its value is 1, the dot is white.

• If you use 24 bits of memory space to control each pixel, you can display more than 16.7 million colors because 16,777,216 combinations are possible with a 4-digit binary number (224=16,777,216).

• If you multiply the number of pixels necessaryfor the screen resolution by the number of bitsrequired to represent each pixel, you have theamount of memory the adapter needs to displaythat resolution.

1024×768 = 786432 pixels×24 bits per pixel

= 18,874,368 bits

= 2,359,296 bytes

= 2.25MBAt 1024×768 resolution requires exactly 2.25MB of RAM on the video adapter.

Amounts of only

256KB, 512KB, 1MB, 2MB, or 4MB

Video Display Adapter Minimum Memory Requirements for 2D

Operations

2D graphics operations, such as photo editing, presentation graphics,

desktop publishing, and Web page design.

video adapter with 4MB can display 65,536 colors in 1600×1200 resolution mode

But to display 16.8 million colors, you would need to upgrade to 8MB

you would need to replace your current video card with a new one with more memory

• 3D video cards require more memory for a

given resolution and color depth because the

video memory must be used for three buffers:

the front buffer, back buffer, and Z-buffer.

Note

• If your system uses integrated graphics and youhave less than 256MB of RAM, you might beable to increase your available graphics memoryby upgrading system memory (system memory isused by the integrated chipset).

• Most recent Intel chipsets with integratedgraphics automatically detect additional systemmemory and adjust the size of graphics memoryautomatically.

Note

• The earliest AGP cards had relatively small

amounts of onboard RAM, but recent and all

current implementations of card-based AGP

use large amounts of on-card memory and use

a memory aperture to transfer data more

quickly to and from the video card’s own

memory.

THE END