Hi,
Or rather, Windows as a Service.
In theory, a 32-bit processor can address up to 64 GB of RAM thanks to PAE
(Physical Address Extension) depending on motherboard and operating system
in use. However, for licensing reasons, 32-bit Windows releases are limited
to slightly above 3 GB of RAM even though the processor can work with about
4.1 billion items at once (source: Windows internals, Seventh Edition part
1); there are other factors involved as well (see below).
In order to use Windows 10 (or for that matter, Windows 8 and later), the
processor must support PAE (see above), SSE2 (Streaming SIMD Extension
version 2), and nx (no execute) for both 32-bit and 64-bit systems, which
has been supported by processors since 2003 (really old Pentium 4 and AMD
processors are hereby excluded). This combination guarantees memory security
to some extent. Additionally, 64-bit systems intended for Windows 8.1 and
later require certain processor instructions to enforce stronger security
and to let Windows use more virtual memory (specifically, compare exchange
128, prefetch, and certain CPU register movement commands, supported by
processors since 2005 or so). Certain Windows 10 features will absolutely
require 64-bit systems (including some crucial enterprise-oriented
features), and the next feature update to Windows 10 includes a feature that
depends on both CPU features and motherboard support (Windows Sandbox, to be
exact, which requires 64-bit processors with more recent virtualization
capabilities which the motherboard must expose to operating systems via
firmware settings).
As for largest RAM one can install (or rather use), as I said above, the OS
may mandate certain limits. The other variable is motherboard: current
motherboards will let you install up to 128 GB of RAM (really high end, that
is), while some boards destined for data centers will accept terabytes of
main memory. Currently 64-bit Windows 10 Home will work with 128 GB of RAM,
while Pro and up will happily take in up to 2 terabytes (2048 GB; there is a
specific version of Windows 10 Pro that'll let you use server-grade
processors and up to 6 TB of RAM for really intensive tasks).
As for use of more resources: yes, some internal Windows features will let
64-bit systems and apps work with more resources. However, you need to
remember that, as processor's native word size changes (how many bits of
information it can process at once), so does RAM requirements to some
extent. On 32-bit systems, a processor can work with up to 4 bytes (8 bit
per byte, thus 32 bits) of information, whereas 64-bit processors will ask
apps to send data in 8 byte chunks (64 bits). In theory, this means 64-bit
apps will require twice more RAM than 32-bit version, and this is aptly
reflected in Windows 10 minimum RAM requirement (1 GB for 32-bit, 2 GB for
64-bit). In reality, 64-bit apps do not take twice more RAM than 32-bit apps
because operating systems and processors can work with smaller data sizes
(the internals of this is best suited for a computer hardware forum than
this one, I think).
Cheers,
Joseph