Lesson 2-1: Central Processing
Unit (CPU)
A CPU’s speed is measured in megahertz (MHz) or, for newer models, in gigahertz (GHz). A megahertz equals millions of cycles per second; a gigahertz equals billions of cycles per second. Higher numbers equate to higher speeds. You might see an Intel Pentium 4 at 3.06 GHz, a Pentium III at 1.40 GHz, and a Celeron at 2.20 GHz. Another common measure of a CPU is how many bits it can handle at a time. A bit is the
tiniest piece of information processed by a computer. Eight bits make up one byte, and one byte equals one character. Computers used to handle 8 or 16 bits; now they’re up to 32 and 64 .
Most people know that a computer has memory, but The first thing you need to know is that, at its most basic level, a computer only understands the concept of “on and off.” On is represented by the number one (1); off is represented by the number zero (0). Everything that a computer does is based on this combination of ones and zeros, which is known as the binary system. These ones and zeros are digits, known as bits,
which are the smallest memory unit. The term bit is short for binary digit. The second thing you need to know is that a computer saves information in bytes, not bits. So what is a byte? The term byte is short for binary digits eight. So one byte is made up of eight bits. And a byte is the equivalent of a character, which can be a letter, a number, or a symbol. So let’s say that you’re a self-involved poet whose latest creation is simply titled “I.” That one-word title would equal one byte. A kilobyte (abbreviated K or KB) equals 1,024 bytes or characters. After the kilobyte, the next largest unit is the megabyte. A megabyte (abbreviated M or MB)
equals 1,048,576 bytes or characters. If you were a novelist, your latest bestseller would equal a megabyte. The next unit after the megabyte is the gigabyte. A gigabyte (abbreviated G or GB) equals 1,073,741,824 bytes or characters. Let’s pretend you are a researcher. A whole shelf of books devoted to your favorite subject would be the equivalent of a gigabyte.
The following table summarizes all the units of memory.
• RAM (random-access memory)
When someone at a computer superstore tells you how much memory a new computer has, they’re really talking about RAM. RAM is the computer’s main memory, which it uses to process information. Whenever you work with a file on your computer, you’re using RAM. And the data in that file is temporarily stored in RAM. However, RAM is volatile, which means that the data is stored only as long as the computer has power. Once you shut off your computer, the data is gone. However, you can and should save your data (read: your file). That’s where storage comes in, but more on that later. For now, think of RAM like a notebook: You can read from it and write to it. Technically, it could be called “read and write memory.” And, as with a notebook, you can overwrite it many, many times—provided you have an eraser!
• ROM (read-only memory)
ROM is the computer’s low-level memory, which it uses to perform its most basic functions. This memory is permanent; the data remains even if you shut off the computer. This only makes sense because ROM is required to restart your computer. You never hear people discuss how much ROM you have because the manufacturer usually installs it, and you never touch it. It does all the behind-the-scenes work and then disappears once you’re underway, much like a party planner. You can also think of ROM like a novel: You
can read from it, but you can’t write to it (and thus, its name).
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