377:, meaning that the act of reading a row also causes the data in it to be erased. To make the data permanent, any reading has to be followed by the DRAM writing the same data back to that row. To accomplish this, separate latches for the entire row have to be included, and the data is written back to the row while the CPU is reading out the requested byte. When one considers the process as a whole, this means the DRAM is repeatedly reading entire rows of data, selecting a single byte from that data and discarding the rest, and then writing it all back again.
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258:(VDC), which sends a timing signal to the memory and receives data in the correct sequence as it draws the screen. Because the CPU and VDC access the memory simultaneously on different ports, dual-ported RAM does not require the CPU to pause while the VDC uses memory, thereby eliminating the associated
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input. To work with such a display it is extremely important that the video hardware output a very accurately timed signal. At the speeds that contemporary memory worked at, reading data to feed to the video hardware used up much of the possible performance of the memory devices. This conflicted with
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VRAM operates by not discarding the excess bits in the row. Instead, the data read into the row storage is also sent to a second set of latches and an associated bit shifter. From that point, the data can be read out a bit at a time by triggering the shifter, and doing so only requires a single pin.
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system, which set a new standard for graphics displays. Prior to the development of VRAM, dual-ported memory was quite expensive, limiting higher resolution bitmapped graphics to high-end workstations. VRAM improved the overall framebuffer throughput, allowing low cost, high-resolution, high-speed,
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Two general solutions were used to avoid timing issues. For higher-priced systems, the video systems had their own dedicated memory and used a separate system for the CPU to store data into it. This eliminated any possibility of contention for memory, but at the cost of requiring separate memory in
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Dual-ported RAM was common from the mid-1980s into the mid-1990s. After that date, new forms of high-performance memory began to be used that eventually replaced dual-ported designs. As these other forms of memory are also known as video memory, and thus VRAM, it sometimes confused with this older
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Such operation is described in the paper "All points addressable raster display memory" by R. Matick, D. Ling, S. Gupta, and F. Dill, IBM Journal of R&D, Vol 28, No. 4, July 1984, pp. 379–393. To use the video port, the controller first uses the DRAM port to select the row of the memory array
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technologies gradually became affordable, dense, and fast enough to displace VRAM, even though it is only single-ported and more overhead is required. Nevertheless, many of the VRAM concepts of internal, on-chip buffering and organization have been used and improved in modern graphics adapters.
385:, meaning that the CPU and graphics still have to interleave their accesses to the chip, but as a whole row of data is read out to the graphics driver, and that row might represent multiple scan lines on the screen, the number of times it has to interrupt the CPU can be greatly reduced.
405:, in strict address order, from the shift register to the video port. For simplicity, the graphics adapter is usually designed so that the contents of a row, and therefore the contents of the shift-register, corresponds to a complete horizontal line on the display.
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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 in a serial fashion. This makes it easy to interface with a
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in 1980, with a patent issued in 1985 (US Patent 4,541,075). The first commercial use of VRAM was in a high-resolution graphics adapter introduced in 1986 by IBM for its
322:(GUIs) that required high resolution and high overall performance, made the performance of the video system an increasingly difficult problem. Complex systems like the
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The solution was to use memory that could be access by the CPU and video hardware at the same time. It was invented by F. Dill, D. Ling and R. Matick at
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315:", but it had the advantage of being less expensive and allowing the CPU to more rapidly update the display and thus provide more interactivity.
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that limited the speed that changes to the screen could be made, making interactive graphics difficult. The other solution, used by most
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emerged to carefully control access to memory and reduce contention, but while these reduced the problem they did not eliminate it.
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By the early 1980s, the introduction of much higher-resolution monitors that demanded larger framebuffers, and the newly introduced
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color graphics. Modern GUI-based operating systems benefitted from this and thus it provided a key ingredient for proliferation of
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Through the 1990s, many graphic subsystems used VRAM, with the number of megabits touted as a selling point. In the late 1990s,
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Please help update this article to reflect recent events or newly available information.
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an era when memory was very expensive. It also almost always communicated over a slow
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that is to be displayed. The VRAM then copies that entire row to an internal
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or a simple conversion of a television that accepted
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101:. Unsourced material may be challenged and removed.
242:(DRAM), which was once commonly used to store the
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366:the requested data so it can be read on the
64:Learn how and when to remove these messages
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342:(GUIs) throughout the world at that time.
262:and improving overall system performance.
215:Learn how and when to remove this message
161:Learn how and when to remove this message
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859:Computer-related introductions in 1980
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498:SM55161A 262144×16 bit VRAM data sheet
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99:adding citations to reliable sources
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186:This article needs to be
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273:Samsung Electronics VRAM
256:video display controller
869:20th-century inventions
297:central processing unit
110:"Dual-ported video RAM"
504:, Austin Semiconductor
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282:Early computers used
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228:Dual-ported video RAM
95:improve this article
864:American inventions
673:Hybrid Memory Cube
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373:DRAM devices are
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112: –
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106:Find sources:
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84:This article
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854:Types of RAM
621:(Mobile DDR)
557:Asynchronous
506:, retrieved
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481:, retrieved
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331:IBM Research
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93:Please help
88:verification
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47:Please help
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579:Synchronous
399:shift clock
393:which is a
375:destructive
346:Description
324:Amiga Agnus
313:wait states
284:dynamic RAM
260:wait states
244:framebuffer
240:dynamic RAM
238:variant of
236:dual-ported
848:Categories
508:2009-03-02
483:2017-06-07
462:References
448:static RAM
391:row-buffer
352:capacitors
305:system bus
288:television
151:April 2009
121:newspapers
50:improve it
828:Bandwidth
769:XDR2 DRAM
592:DDR SDRAM
56:talk page
764:XDR DRAM
682:Graphics
569:EDO DRAM
564:FPM DRAM
422:See also
403:data bit
368:data bus
797:UniDIMM
661:HBM-PIM
627:(FCRAM)
364:latches
278:History
234:) is a
188:updated
135:scholar
751:Rambus
636:RLDRAM
551:(DRAM)
137:
130:
123:
116:
108:
811:Lists
759:RDRAM
739:GDDR7
734:GDDR6
729:GDDR5
724:GDDR4
719:GDDR3
714:GDDR2
704:SGRAM
699:MDRAM
666:HBM3E
651:HBM2E
631:eDRAM
619:LPDDR
587:SDRAM
502:(PDF)
434:Notes
335:RT PC
142:JSTOR
128:books
802:CAMM
792:DIMM
787:SIMM
709:GDDR
694:WRAM
689:VRAM
656:HBM3
646:HBM2
612:DDR5
607:DDR4
602:DDR3
597:DDR2
360:byte
356:cell
232:VRAM
114:news
641:HBM
450:or
246:in
97:by
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