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HARDWARE
DATA AND PROGRAM REPRESENTATION
Chapter Objective 1:
Most digital computers work in a two-state, or binary, fashion. It is convenient to think of these binary states in terms of 0s and 1s. Computer people refer to these 0s and 1s as bits.
Converting data to these 0s and 1s is called digital data representation.
While most individuals use the decimal number system to represent numbers and
perform numeric computations, computers use the binary numbering system. Text-based
data can be represented with one of several fixed-length binary codes. Two possible coding
schemes are ASCII (American Standard Code for Information Interchange) and
EBCDIC (Extended Binary-Coded Decimal Interchange Code). These systems repre-
sent single characters of data—a numeric digit, alphabetic character, or special symbol—
as strings of bits. Each string of eight bits is called a byte. Unicode is a newer coding
system that can represent text in all written languages, including those that use alphabets
different from English, such as Chinese, Greek, and Russian.
The storage capacity of computers often is expressed in kilobytes (KB), or thousands of
bytes; megabytes (MB), millions of bytes; gigabytes (GB), billions of bytes; and terabytes
(TB), trillions of bytes. Other possibilities are the petabyte (PB), about 1,000 terabytes; the
exabyte (EB), about 1,000 petabytes; the zettabyte (ZB), about 1,000 exabytes; and the
The binary system can represent not only text but also graphics, audio, and video data.
Machine language is the binary-based code through which computers represent program
instructions. A program must be translated into machine language before the computer can
execute it.
INSIDE THE SYSTEM UNIT
Chapter Objective 2:
PCs typically contain a variety of hardware components located inside the system unit.
For instance, chips are mounted onto circuit boards, and those boards are positioned in slots on the motherboard or system board—the main circuit board for a PC. Every PC has
a central processing unit (CPU)—also called a processor or a microprocessor when
referring to PCs—attached to its motherboard that performs the processing for the com- puter. CPU chips differ in many respects, such as what types of PCs the CPU is designed for, its clock speed, and word size. They can also be multi-core CPUs, such as the dual-
core
(two cores) and quad-core (four cores) CPUs now available. Another difference is
the amount of cache memory—memory located on or very close to the CPU chip to help
speed up processing. Other important differences are the general architecture of the CPU
and the bus speed and width being used. The overall processing speed of the computer
determines its performance. One of the most consistent measurements of overall perform-
ance is a benchmark test.
The main memory chips for a PC are commonly referred to as RAM (random access
memory). RAM is volatile and used to temporarily hold programs and data while they are
needed. RAM is available in different types and speeds. ROM (read-only memory) are
memory chips that store nonerasable programs. Flash memory is nonvolatile memory that
can be erased and reprogrammed in blocks. Flash memory chips can be found in PCs and
mobile devices; flash memory chips can also be used for storage with portable PCs, digital
cameras, and other smaller devices. Registers are memory built into the CPU chip to hold
data before or during processing.
CHAPTER 2 THE SYSTEM UNIT: PROCESSING AND MEMORY
Most desktop PCs contain internal expansion slots, into which users can insert
Chapter Objective 3:
expansion cards to give the computer added functionality. A computer bus is an electronic
path along which bits are transmitted. The parts of the system bus (the frontside bus and the memory bus) move data between the CPU and RAM, and expansion buses connect the
CPU to peripheral devices. Common buses include PCI, PCI Express (PCIe), AGP,
HyperTransport, Universal Serial Bus (USB), and FireWire.
System units typically have external ports that are used to connect peripheral devices
to the computer. Notebook and tablet PCs may have fewer ports than desktop PCs. Hand-
held PC and mobile device users often add new capabilities with Secure Digital (SD) cards
or other types of flash memory cards. ExpressCard modules can be used to add additional
capabilities to PCs containing an ExpressCard slot. Some handheld PCs and mobile
devices have a proprietary expansion system.
HOW THE CPU WORKS
CPUs today include at least one arithmetic/logic unit (ALU), which performs integer
Chapter Objective 4:
arithmetic and logical operations on data, and most include at least one floating point unit
(FPU), which performs decimal arithmetic. The control unit directs the flow of electronic
traffic between memory and the ALU/FPU and also between the CPU and input and output devices. Registers—high-speed temporary holding places within the CPU that hold pro- gram instructions and data immediately before and during processing—are used to
enhance the computer’s performance. The prefetch unit requests data and instructions
before or as they are needed, the decode unit decodes the instructions input into the CPU,
internal cache stores frequently used instructions and data, and the bus interface unit
inputs data and instructions from RAM.
The CPU processes instructions in a sequence called a machine cycle, consisting of
four basic steps. Each machine language instruction is broken down into several smaller
instructions called microcode, and each piece of microcode corresponds to an operation
(such as adding two numbers located in the CPU’s registers) that can be performed inside
the CPU. The computer system has a built-in system clock that synchronizes all of the
PC’s activities.
MAKING COMPUTERS FASTER AND BETTER NOW AND IN
THE FUTURE

There are several possible remedies for a computer that is performing too slowly, including Chapter Objective 5:
adding more memory, performing system maintenance to clean up the PC’s hard drive, buying a larger or additional hard drive, and upgrading the computer’s Internet connection or video card, depending on the primary role of the computer and where the processing bottleneck appears to be. To make computers work faster overall, computer designers have developed a number of strategies over the years, and researchers are continually working
on new strategies. Some of the strategies already being implemented include improved
architecture, pipelining, multiprocessing, parallel processing, and the use of improved
materials.
One possibility for future computers is nanotechnology research, which focuses on
Chapter Objective 6:
building computer components at the individual atomic and molecular levels. Some products (such as NRAM and bikes) using carbon nanotubes are currently on the market.
Quantum computing and optical computers are other possibilities being researched,
along with three-dimensional (3D) chips.