CompTIA A_ Certification All-In-One Exam Guide, Seventh Edition - Michael Meyers [68]
* * *
NOTE Bits and bytes are abbreviated differently. Bytes get a capital B whereas bits get a lowercase b. So for example, 4 KB is four kilobytes, but 4 Kb is four kilobits.
Which Pattern Goes to Which Row?
The second question is a little harder: “Which pattern goes to which row of RAM?” To understand this, let’s take a moment to discuss binary counting. In binary, only two numbers exist, 0 and 1, which makes binary a handy way to work with wires that turn on and off. Let’s try to count in binary: 0, 1…what’s next? It’s not 2—you can only use zeros and ones. The next number after 1 is 10! Now let’s count in binary to 1000: 0, 1, 10, 11, 100, 101, 110, 111, 1000. Try counting to 10000. Don’t worry; it hardly takes any time at all.
Super; you now count in binary as well as any math professor. Let’s add to the concept. Stop thinking about binary for just a moment and think about good old base 10 (regular numbers). If you have the number 365, can you put zeros in front of the 365, like this: 000365? Sure you can—it doesn’t change the value at all. The same thing is true in binary. Putting zeroes in front of a value doesn’t change a thing! Let’s count again to 1000 in binary. In this case, add enough zeros to make 20 places:
00000000000000000000
00000000000000000001
00000000000000000010
00000000000000000011
00000000000000000100
00000000000000000101
00000000000000000110
00000000000000000111
00000000000000001000
Hey! This would be a great way to represent each line of RAM on the address bus, wouldn’t it? The CPU identifies the first byte of RAM on the address bus with 00000000000000000000. The CPU identifies the last RAM row with 11111111111111111111. When the CPU turns off all of the address bus wires, it wants the first line of RAM; when it turns on all of the wires, it wants the 1,048,576th line of RAM. Obviously, the address bus also addresses all of the rows of RAM in between. So, by lighting up different patterns of ones and zeros on the address bus, the CPU can access any row of RAM it needs.
Essentials
Modern CPUs
Modern CPUs retain the core structures of the Intel 8088, such as registers, instruction sets, and, of course, the arithmetic logic unit (ALU)—our friend, the Man in the Box. But in the decades of the personal computer, many manufacturers have risen to challenge Intel’s dominance—some have even survived—and all processor makers have experimented with various processor shapes, connectors, and more. The amazing variety of modern CPUs presents unique challenges to a new tech. Which processors go on which motherboards? Can a motherboard use processors from two or more manufacturers? Aren’t processors all designed for PCs and thus interchangeable?
This section maps out the modern processor scene. It starts with a brief look at the manufacturers so you know who the players are. Once you know who’s making the CPUs, we’ll go through the generations of CPUs in wide use today, starting with the Intel Pentium. All modern processors share fundamental technology first introduced by Intel in the Pentium CPU. I use the Pentium, therefore, to discuss the details of the shared technology, and then add specific bonus features when discussing subsequent processors.
Manufacturers
When IBM awarded Intel the contract to provide the CPUs for its new IBM PC back in 1980, it established for Intel a virtual monopoly on all PC CPUs. The other home-computer CPU makers of the time faded away: MOS Technology, Zilog, Motorola—no one could compete directly with Intel. Over time, other competitors have risen to challenge Intel’s market-segment share dominance. In particular, a company called Advanced Micro Devices (AMD) began to make clones of Intel CPUs, creating an interesting and rather cutthroat competition with Intel that lasts to this day.
Intel
Intel