Midterm 2 Summary.doc

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14 Dec 2013
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Technology Guide 1: Computer Hardware
Decisions about hardware focus on three interrelated factors: Capability (power and
appropriateness for the task), Speed, and Cost.
Hardware refers to the physical equipment used for the input, processing, output and storage
activities of a computer system. It consists of the following:
oCentral processing unit (CPU) manipulates the data and controls the tasks performed by
the other components.
oPrimary storage internal to the CPU; temporarily stores data and program instructions
during processing.
oSecondary storage external to the CPU; stores data and programs for future use.
oInput technologies accept data and instructions and convert them to a form that the
computer can understand.
oOutput technologies present data and information in a form people can understand.
oCommunication technologies provide for the flow of data from external computer
networks (e.g. the Internet and intranets) to the CPU, and from the CPU to computer
networks.
Central Processing Unit (CPU)
Central processing unit (CPU) performs the actual computation or “number crunching” inside
any computer. The CPU is a Microprocessor (Intel Pentium 4 or Centrino) made up of millions
of microscopic transistors embedded in a circuit on a silicon chip.
Control unit sequentially accesses program instructions, decodes them and controls the flow of
data to and from the ALU, the registers, the caches, primary storage, secondary storage and
various output devices.
Arithmetic-logic unit (ALU) performs the mathematic calculations and makes logical
comparisons.
Registers are high-speed storage areas that store very small amounts of data and instructions for
short periods of time.
The CPU can process only Binary form – data and
instructions only consists of 0 and 1.
Machine instruction cycle: The cycle of computer
processing, whose speed is measured in terms of the
number of instructions a chip processes per second. It
occurs millions of times per second or more. Processing
speed depends on the following four factors of chip
design:
Clock speed – the preset speed of the computer clock that times all chip activities, measured in
megahertz (MHz, millions of cycles per second) and gigahertz (GHz, billions of cycles per
second). The faster clock speed, the faster the chip or computer speed.
Word length: The number of bits (0s and 1s) that can be processed by the CPU at any one time.
It can be 32-bit or 64-bit word lengths, and the larger the word length, the faster the chip or
computer speed.
Bus width: The size of the physical paths down which the data and instructions travel as
electrical impulses on a computer chip. The wider or bigger the bus, the more data can be
transferred and the faster the processing.
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The number of transistors on the chip depend on the Line width - the distance between
transistors (in nanometres, billionths of a meter). The smaller the line width, the more number of
transistors on the chip, and the faster the chip or computer speed.
Moore’s Law predicted in 1965 that microprocessor complexity would double approximately
every two years, (his prediction has been amazingly accurate) as a result of the following
changes:
oIncreasing miniaturization of transistors.
oDecreasing line width - making the physical layout of the chip’s components as compact
and efficient as possible.
oUsing materials for the chip that improve the conductivity (flow) of electricity, e.g.
gallium arsenide and silicon germanium.
oTargeting the amount of basic instructions programmed into the chip. Tow most common
microprocessor architectures are CISI (complex instruction set computing) and RISI
(Reduced instruction set computing)
oPlacing multiple processors on a single chip – Multicore chips, e.g. Intel Core 2 Duo or
Intel Dual-Core.
Microcontrollers are computer chips, embedded in products and technologies (cell phone, toys,
etc.), that usually cost less and work in less-demanding applications than microprocessors.
Computer Memory
There are two basic categories of computer memory: Primary Storage and Secondary Storage.
Primary stores small amounts of data and information that will be immediately used by the CPU.
Secondary stores much larger amounts of data and information (an entire software program, for
example) for extended periods of time.
Memory Capacity:
oBit: Short for binary digit (0s and 1s), the only data that a CPU can process.
oByte: An 8-bit string of data, needed to represent any one alphanumeric character or
simple mathematical operation.
oKilobyte (KB): approximately one thousand bytes.
oMegabyte (MB): approximately one million bytes (1,048,576 bytes, or 1,024 x 1,024).
oGigabyte (GB): approximately one billion bytes, actually 1,073,741,824 bytes (1,024 x
1,024 x 1,024 bytes).
oTerabyte: approximately One trillion bytes.
oPetabyte: Approximately 1015 bytes.
oExabyte: Approximately 1018 bytes.
Primary Storage
Primary storage or main memory stores three types of information for very brief periods of
time:
1. Data to be processed by the CPU
2. Instructions for the CPU as to how to process the data
3. Operating system programs that manage various aspects of the computer’s operation.
Primary storage takes place in chips mounted on the computer’s main circuit board, called the
motherboard. All data and instructions in primary storage have been translated into binary code.
Four main types of primary storage:
1. Registers: registers are part of the CPU with the least capacity, storing extremely limited
amounts of instructions and data only immediately before and after processing.
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2. Random Access Memory (RAM): The part of primary storage that holds a software
program and small amounts of data when they are brought from secondary storage. RAM
is temporary and volatile – lose data if power is off. Two main type of RAM: Dnaymic
RAM (DRAM – slow but cheap) and Static RAM (SRAM fast but expensive). Other type
is Magnetic RAM (MRAM, less electricity consumed, combined high speed of SRAM,
storage capacity of DRAM and the nonvolatility of flash memory)
3. Cache Memory: A type of high-speed primary storage that enables the computer to
temporarily store blocks of data that are used more often and that a processor can access
more rapidly than main memory (RAM). There are three types of Cache memory: Level 1
(L1), Level 2 (L2), Level 3 (L3). L1 and L2 caches are located in the processor, and L3
cache is located on motherboard, L1 is smaller and faster than L2, which is in turn smaller
and faster then L3.
4. Read-Only Memory (ROM): Type of primary storage where certain critical instructions
are safeguarded; the storage is nonvolatile and retains the instructions when the power to
the computer is turned off. Flash memory is a form of rewritable read-only memory that
is compact, portable, and requires little energy.
Secondary Storage
Secondary Storage is memory capacity that can store very large amounts of data for extended
periods of time. The overall trends in secondary storage are toward more direct-access methods,
higher capacity with lower costs, and increase portability. It has the following characteristics:
oIt is nonvolatile.
oIt takes much more time to retrieve data because of the electromechanical nature.
oIt is cheaper than primary storage.
oIt can take place on a variety of media
Magnetic Media
Magnetic Tape is a secondary storage medium kept on a large open reel or in a smaller cartridge
or cassette. It’s an old technology, but popular because of it’s a cheapest storage medium and can
handle enormous amounts of data. However, it uses the slowest method for retrieving data
because the data are placed on the tape sequentially, i.e., Sequential access – data access in
which the computer system must run through data in sequence in order to locate a particular
piece. So, magnetic tape is best or data which rarely use or does not need immediate access to.
Magnetic Disks are a form of secondary storage on a magnetized disk divided into tracks and
sectors that provide addresses for various pieces of data; also called Hard Disks or Hard Drives.
(a form of secondary storage that stores data on platters divided into concentric tracks and sectors,
which can be read by a read/write head that pivots across the rotating disks). Hard Disks are the
most commonly used because of low cost, high speed, and large storage capacity.
Data stored and access in hard disks is Direct access - data access in which any piece of data be
retrieved in a non-sequential manner by locating it using the data’s address. Be aware of loss data
occur by a disk crash. Most PCs use two high-performance disk interface standards: Enhanced
Integrated Drive Electronic (EIDE, inexpensive, good performance, supports to 4 disks, tapes or
CD-ROM) and Small Computer System Interface (SCSI, more expensive, faster and support
more devices, more common uses for graphics, server-based or large database)
Magnetic diskettes or Floppy disks is a form of easily portable secondary storage on flexible
Mylar disks. Much slower than hard disks, less capacity (only 1.44 MB), individually cheap but
cost more in term of its small storage. Big advantage is portable.
Optical Storage Devices
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