CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [79]
Intel Core Duo (see the “Intel Core” section later in the chapter.)
A mobile processor uses less power than an equivalent desktop model. This provides two advantages. First, the battery in the laptop lasts longer. Second, the CPU runs cooler, and the cooler the CPU, the fewer cooling devices you need.
Almost every mobile processor today runs at a lower voltage than the desktop version of the same CPU. As a result, most mobile CPUs also run at lower speeds—it takes juice if you want the speed! Mobile CPUs usually top out at about 75 percent of the speed of the same CPU’s desktop version.
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TIP Intel uses the marketing term Centrino in the laptop market to define complete mobile solutions, including a mobile processor, support chips, and wireless networking. There is no Centrino CPU, only Centrino solutions that include some type of Intel mobile CPU.
Reducing voltage is a good first step, but making a smart CPU that can use less power in low-demand situations reduces power usage even more. The first manifestation of this was the classic System Management Mode (SMM). Introduced back in the times of the Intel 80386 processor, SMM provided the CPU with the capability to turn off devices that use a lot of power, such as the monitor or the hard drives. Although originally designed just for laptops, SMM has been replaced with more advanced power-management functions that are now built into all AMD and Intel CPUs.
CPU makers have taken power reduction one step further with throttling—the capability of modern CPUs to slow themselves down during low demand times or if the CPU detects that it is getting too hot. Intel’s version of throttling is called SpeedStep, and AMD’s version is known as PowerNow!
Early 64-Bit CPUs
Both AMD and Intel now produce 64-bit CPUs. A 64-bit CPU has general-purpose, floating point, and address registers that are 64 bits wide, meaning they can handle 64-bit-wide code in one pass—twice as wide as a 32-bit processor. And they can address much, much more memory.
With the 32-bit address bus of the Pentium and later CPUs, the maximum amount of memory the CPU can address is 232 or 4,294,967,296 bytes. With a 64-bit address bus, CPUs can address 264 bytes of memory, or more precisely, 18,446,744,073,709,55 1,616 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 (260). A 64-bit address bus can address 16 exabytes of RAM.
No 64-bit CPU uses an actual 64-bit address bus. Every 64-bit processor gets its address bus clipped down to something reasonable. The Intel Itanium, for example, only has a 44-bit address bus, for a maximum address space of 244 or 17,592,186,044,416 bytes. AMD’s Phenom II, on the other hand, can allow for a 48-bit physical address space for 248 or 281,474,976,710,656 bytes of memory.
Initially, both AMD and Intel raced ahead with competing 64-bit processors. Interestingly, they took very different paths. Let’s look at the two CPUs that made the first wave of 64-bit processing: the Intel Itanium and the AMD Opteron.
Intel Itanium (Original and Itanium 2)
Intel made the first strike into the 64-bit world for PCs with the Itanium CPU. The Itanium was more of a proof-of-concept product than one that was going to make Intel any money, but it paved the way for subsequent 64-bit processors. The Itanium had a unique 418-pin pin array cartridge (PAC) to help house its 2- or 4-MB Level 3 cache (Figure 5-49).
Figure 5-49 Intel Itanium (photo courtesy of Intel)
The Intel Itanium 2 was Intel’s first serious foray into the 64-bit world. To describe the Itanium 2 in terms of bus sizes and clock speeds is unfair. The power of this processor goes far deeper. Massive pipelines, high-speed caching, and literally hundreds of other improvements make the Itanium 2 a powerful CPU for high-end PCs. The Itanium 2 uses a unique form