Windows 10 won't help PC sales this year - in fact, it might hurt

The upcoming release of Microsoft's new operating system, Windows 10, will slow, not boost, PC sales growth this year, market research firm Gartner wrote in a new report Monday.

According to the report, the global PC shipment market is expected to shrink 4.5% this year from the previous year, to a total of 300 million units worldwide. That's a drop of 1.3 percentage points from Gartner's last estimate.

Gartner said the "continued slowdown in PC purchases in Western Europe, Russia, and Japan" have contributed to the lower forecast.

But the release of Windows 10 will also play into it.

"The release of Windows 10 on 29th July will contribute to a slowing professional demand for mobile PCs and premium ultramobiles in 2015, as lifetimes extend by three months," Gartner analyst Ranjit Atwal wrote.

In plain English? Most people who want Windows 10 will just update the software, taking advantage of Microsoft's offer of a free upgrade for all Windows 7 and Windows 8.1 users, rather than buying a new PC. That will extend the average lifetime of current PCs by three months, Gartner believes.

But by the fall, a new wave of Windows 10 PCs at lower prices might spur growth. "However, as suppliers and buyers adjust to new prices, Windows 10 could boost replacements during 2016."

The tablet and clamshell market is also expected to contract this year, the report said. Total global shipments will drop 5.3% to 214 million units in 2015, although before bouncing back in 2016 to 228 million total units shipped.

"The tablet market is hit by fewer new buyers, extended life cycles and little innovation to encourage new purchases...The tablet has become a 'nice to have' device, and there is no real need for an upgrade as regularly as for the phone," Gartner analyst Robert Cozza said.

The mobile phone market is expected to grow slightly, but at a slowing rate of 3.3% this year.

As a result, Gartner slashed its growth forecast for the total devices market to 1.5% this year, down from the previous forecast of 2.8% growth it released last quarter. It also said total spending on devices will see a 5.7% decline - the first time since 2010 - to $606 million in 2015.

The new forecasts are in-line with what other companies have warned recently. Chipmaker AMD just announced on Monday that it expects an 8% drop in revenue this quarter from last year, cutting nearly $50 million in its quarterly revenue forecast. Intel CEO Brian Krzanich said in May that he thinks the PC market to be "flat to slightly down mid single-digits over the long-term," despite the Windows 10 upgrades expected this year.

Here's the chart with Gartner's predictions of number of devices shipped, in millions.