The Register has heard from HP and the rumours are indeed true; you will be able to pre-orderd devices from them with which will arrive with Windows 10 installed on July 29th, they will even cover shipping within the US for you.  Retail stores are unlikely to have them that early, more likely you will see them arriving the following week depending on when the store's scheduled shipping date is.  The mid-August into October date that was quoted is specifically for business customers and does not apply to the stores or the website.  The tight turn around gives you a look at how desperate computer retailers are, and Microsoft as well for that matter, to increase flagging sales.

"HP got on the phone with The Register on Wednesday to shed light on how it plans to roll out PCs with Windows 10 preinstalled. The IT giant said you can expect at least some of its hardware to be available with the new OS on the day that it launches – July 29."

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