Microsoft seems to have dropped support for PCs running Intel Pentium III processors. According to a report by ZDNet, the reason for this is because Pentium III-powered PCs do not support SSE2 or Streaming SIMD Extensions 2. For perspective, Intel announced Pentium 4 back in August 2000 along with support for SSE2. This allowed the processor “to process multimedia in parallel, thereby speeding performance”. Four years after the launch, SSE2 was available in “every mainstream processor”. The problem started with the March 2018 security fix for Windows 7 with code KB4088875 where the company noted that it does not support PCs without SSE2 support.
The company updated the corresponding knowledge base article for the security fix pointing out that it “is working on a resolution and will provide an update in an upcoming release.” Later, the company changed the line to “Update your machines with a processor that supports SSE2 or virtualize those machines.” This effectively meant that the security fix did not support Pentium III. It is not surprising that Microsoft has dropped support for processors that do not support SSE2 as the company announced SSE2 as one of the three mandatory CPU features to run its new operating system.
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Windows 10 comes with same requirements of mandatory support for SSE2. As pointed out by the report, Microsoft is well in its rights to drop support for older products as its policy notes that “older products may not meet today’s more demanding security requirements.” The policy goes on to add that “Microsoft may be unable to provide security updates for older products.”
It is likely that Windows 7 machines that are running on Pentium III processors are unable to install cumulative security patches for the system because of not supporting minimum “security requirements”.