1. The Central Processing Unit: What Goes on Inside the Computer
Chapter 4
The Central Processing Unit: What Goes on Inside the Computer

2. CPU CPU - central processing unit
electronic circuitry designed to execute instructions
composed of control unit and ALU
all computers must have at least one
control unit - coordinates and controls all parts of the computer system
manages the machine cycle
ALU (arithmetic logic unit) - performs required arithmetic and logic operations
registers - special-purpose, high-speed, temporary storage associated with CPU

3. Terms associated with the CPU
system unit - case that houses the electronic components of the computer
motherboard - circuit board that typically contains the CPU, support chips, RAM, and expansion slots
microprocessor - an integrated circuit that contains the control unit and ALU of a CPU

4. Terms associated with the CPU
machine cycle - steps performed by the CPU to execute an instruction
fetch, decode, execute, store
system clock - internal clock that pulses at a fixed rate to synchronize computer operations
instruction set - specific group of instructions a CPU is designed to understand
bus - set of electrical paths that transport signals from one part of the system to another
bus width - number of bits that can be carried at one time

5. Processor Speeds
microprocessor speeds - usually determined by clock speed
measured in megahertz (MHz) and gigahertz (GHz)
may also be expressed in MIPS or megaflops
cache - very high speed memory used to store instructions that have been recently or frequently used

6. Strategies to Improve Speed
RISC - reduced instruction set approach to processor design
parallel processing - multiple processors working simultaneously
capable of processing speeds in teraflops
strategy used for designing and building supercomputers

7. Data Representation
Everything stored in the computer is represented using the binary system (base 2) - sequences of 0’s and 1’s
bit - an single binary digit (0 or 1)
byte - a group of 8 bits
needed to store a character
word - number of bits processed by the CPU as a unit

8. Larger measures of storage
Kilobyte (KB) - about 1,000 bytes
megabyte (MB) - about 1 million bytes
gigabyte (GB) - about 1 billion bytes
terabyte (TB) - about 1 trillion bytes

9. Collating Codes
collating code (coding scheme) - a common scheme for assigning a specific series of bits to a specific character
ASCII - most widely used code
used by most PC’s
EBCDIC - used mostly on IBM mainframes
Unicode - uses 2 bytes/character
can handle alphabets used throughout the world

10. Memory
Memory - part of the computer that holds program instructions and data currently being used
also referred to as -
primary storage, primary memory, main memory, internal memory, internal storage
closely associated with the CPU
composed of RAM and ROM

11. RAM - random access memory
used to store instructions and data for currently active programs
can be accessed very quickly by the CPU
usually volatile - power must be on to retain contents
can be erased and written over
128MB common for current PC’s

12. ROM - read only memory
contains programs and data that are permanently stored
can be accessed, but cannot be changed
used to store boot routine (activated when computer is turned on)
nonvolatile - does not lose its contents when the power is turned off