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Each screen character is represented by two bytes aligned as a 16-bit word accessible by the CPU in a single operation. The lower (or character) byte is the actual code point for the current character set, and the higher (or attribute) byte is a bit field used to select various video attributes such as color, blinking, character set, and so forth. [6]
Dual-ported video RAM (VRAM) is a dual-ported RAM variant of dynamic RAM (DRAM), which was once commonly used to store the Framebuffer in Graphics card, . Dual-ported RAM allows the CPU to read and write data to memory as if it were a conventional DRAM chip, while adding a second port that reads out data.
Video random-access memory (VRAM) is dedicated computer memory used to store the pixels and other graphics data as a framebuffer to be rendered on a computer monitor. [1] It often uses a different technology than other computer memory, in order to be read quickly for display on a screen.
Set text-mode cursor shape AH=01h CH = Scan Row Start, CL = Scan Row End Normally a character cell has 8 scan lines, 0–7. So, CX=0607h is a normal underline cursor, CX=0007h is a full-block cursor. If bit 5 of CH is set, that often means "Hide cursor". So CX=2607h is an invisible cursor. Some video cards have 16 scan lines, 00h-0Fh.
The color information for each point thus displayed on the screen is pulled directly from the framebuffer during the scan, creating a set of discrete picture elements, i.e. pixels. Framebuffers differ significantly from the vector displays that were common prior to the advent of raster graphics (and, consequently, to the concept of a framebuffer).
Video memory was shared with the first 128 KiB of RAM. The exact size of the video memory could be reconfigured by software to meet the needs of the current program. An early hybrid system was the Commodore Amiga which could run as a shared memory system, but would load executable code preferentially into non-shared "fast RAM" if it was available.
Similar displays in the Task Manager of Windows Vista and later have been changed to reflect usage of physical memory. In Task Manager's "Processes" display, each process's contribution to the "total commit charge" is shown in the "VM size" column in Windows XP and Server 2003. The same value is labeled "Commit size" in Windows Vista and later ...
WDDM drivers allow video memory to be virtualized, [6] and video data to be paged out of video memory into system RAM. In case the video memory available turns out to be insufficient to store all the video data and textures, currently unused data is moved out to system RAM or to the disk. When the swapped out data is needed, it is fetched back.