(Reuters) - Worries about how fast the computing world will transition to Nvidia Corp's NVDA.O next generation "Turing" graphic chips helped knock 20 percent off the value of its shares on Friday, after results pointed to a huge glut of unsold older generation chips.

FILE PHOTO - The logo of technology company Nvidia is seen at its headquarters in Santa Clara, California February 11, 2015. REUTERS/Robert Galbraith

The world’s biggest maker of graphics cards for computer gaming pinned the blame for a disappointing holiday forecast on unsold “Pascal” chips piling up with distributors and retailers after the evaporation of the cryptocurrency mining boom.

Wall Street analysts, responding to Thursday’s results, said poor sales were likely to continue for at least a couple of quarters until the generally well-reviewed Turing technology takes hold with software and hardware makers.

“We think that history will show Turing as a breakthrough product,” Morgan Stanley analyst Joseph Moore wrote in a client note. “But it will take time for software to take full advantage of the chip.”

Shares in Nvidia were set to open at their lowest in a year, falling 18 percent in trading before the opening bell. At least 14 brokerages lowered their price targets on the company, with BMO Capital Markets the most dour, cutting its price target to $175 from $225.

None of the 37 brokerages covering the stock cut their ratings, however. Twenty-six now have a “buy” or higher rating on the stock and the rest are on “hold.”

Nvidia's Turing chips feature ray tracing here technology that helps game creators to make real-time cinema-quality visuals by simulating the physical behavior of light.

Electronic Art's EA.O Battlefield V, set for release later this month, will support Nvidia's ray tracing technology and a series of other blockbuster titles should follow next year.

Turing-based GPUs have been widely stocked out in response, but in the transition Nvidia has also stopped shipping some of its mid-priced Pascal graphics processing units (GPUs) to retailers to reduce the inventory glut in its supply chain, weakening revenues.

Nvidia said on Thursday it expected current-quarter revenue of $2.7 billion, plus or minus 2 percent, well below analysts’ average estimate of $3.40 billion, according to IBES data from Refinitiv.