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CompTIA A+ Certification All-in-One Exam Guide

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64-Bit Processing

Over successive generations of microprocessors, engineers have upgraded

many physical features of CPUs. The EDB gradually increased in size, from

8- to 16- to 32- to 64-bits wide. The address bus similarly jumped, going

from 20- to 24- to 32-bits wide (where it stayed for a decade).

The technological features changed as well. Engineers added new and

improved registers, for example, that used fancy names like multimedia

extensions (MMX) and Streaming SIMD Extensions (SSE). A mighty shift

started several years ago and continues to evolve: the move to 64-bit

computing.

Most new CPUs support 64-bit processing, meaning they can run a

compatible 64-bit operating system, such as Windows 10, and 64-bit

applications. They also support 32-bit processing for 32-bit operating

systems, such as some Linux distributions, and 32-bit applications. The

general-purpose registers also make the move up to 64-bit. The primary

benefit to moving to 64-bit computing is that modern systems can support

much more than the 4 GB of memory supported with 32-bit processing.

With a 64-bit address bus, CPUs can address 2 64 bytes of memory, or

more precisely, 18,446,744,073,709,551,616 bytes of memory—that’s a lot

of RAM! This number is so big that gigabytes and terabytes are no longer

convenient, so we now go to an exabyte (2 60 ), abbreviated EB. A 64-bit

address bus can address 16 EB of RAM.

In practical terms, 64-bit computing greatly enhances the performance of

programs that work with large files, such as video editing applications. You’ll

see a profound improvement moving from 4 GB to 8 GB or 16 GB of RAM

with such programs.

EXAM TIP The primary benefit of 64-bit computing is to support more

than 4 GB of memory, the limit with 32-bit processing.

x86 CPUs from the early days can be lumped together as x86 CPUs,

because they used an instruction set that built upon the earliest Intel CPU

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