Windows Vista was a shock to many Windows users, as its hardware requirements represented a steep upgrade over those required to run Windows XP: most 32-bit versions required a 1GHz processor, 1GB RAM, DirectX 9 graphics, and 40 GB of mass storage with 15GB free. But those 2006-era requirements looked much less steep once Windows 7 rolled out in 2009: it required almost the same system specs, but now 16GB of available disk space instead of 15. Windows 8 again stuck with the same specs and, at its release, so did Windows 10.
But the Windows 10 Anniversary Update (referred to in documentation as version 1607, so it ought to ship in July) changes that, with the first meaningful change in the Windows system requirements in almost a decade. The RAM requirement is going up, with 2GB the new floor for 32-bit installations. This happens to bring the system in line with the 64-bit requirements, which has called for 2GB since Windows 7.
The changed requirements were first spotted by Nokia Power User and WinBeta.
These hardware demands are only particularly relevant for system builders; they'll need to meet the new specs for machines that ship with Windows 10 preinstalled. Windows will still install and run on machines with less than 2GB; it'll just run better on systems with more memory.
This isn't the only hardware change that comes this summer. The initial Windows 10 specifications said that after July 28, all new systems must ship with Trusted Platform Module (TPM) 2.0. The TPM is used for various cryptographic purposes, including storing disk encryption keys. Until this cut-off date, OEMs could choose between TPM 1.2 and 2.0; TPM 2.0 adds a number of additional encryption capabilities to the 1.2 version.
The new specs also change the acceptable screen sizes for Windows 10. Previously, Windows 10 Mobile could ship on phones and tablets with screens up to 7.9 inches, with full Windows 10 on devices with screens of 8 inches or greater. Both of these ranges are now expanded, with Windows 10 Mobile accepted on screens less than 9 inches, and desktop Windows 10 now allowed on anything with a screen of 7 inches or greater.
Previous updates to the specs enabled the support for Qualcomm's new Snapdragon 820 in Windows Mobile. However, ARM support remains stubbornly restricted to 32-bit, with no 64-bit support for any of the 64-bit ARM processors. Microsoft representatives said at its Build conference in 2015 that a 64-bit ARM compiler was in development, and the company hinted that it would become available by the end of last year. It seems that it is still not finished.
Update: Several readers have pointed out that in addition to these spec changes, Windows 8 introduced some additional requirements from the processors, mandating the support of SSE2 and non-executable memory. While this had no impact at all on preinstalled software (as processors without these features had long since ceased production), they did have some significance for those hoping to upgrade very old machines to the new operating system.