The
Central Processing Unit
What Goes on Inside the Computer
The Central Processing Unit
- Control Unit (CU)
- Manages computer's operations.
- Must communicate with both the Arithmetic/Logic Unit and memory
- Arithmetic/Logic Unit (ALU)
- Arithmetic operations including addition, subtraction, multiplication,
division.
- Logical operations - comparisons (=, <, >).
- High speed, temporary storage area used by the CPU for instructions
or data.
- Accumulator register
- collects the results of computations
- Address register
- keeps track of where an instruction or data is stored in memory
- Storage register
- holds data taken from or about to be sent to memory
- General purpose register
- used for several functions, such as arithmetic operations
- Computers use the two-state binary system.
- The binary system contains two digits, 0 and 1, also represented
by on/off, yes/no, etc..
- Each 0 or 1 is called a bit (for binary digit).
- 1 bit = 1 binary digit (0 or 1, on/off)
- 1 byte = group of 8 bits = 1 character
- 1 kilobyte = 1 Kbyte = 1K = 1024 (2^10) bytes (approx. 1 thousand
bytes)
- 1 megabyte = 1 Mbyte = 1Meg = 1,024 Kbytes = 1,048,576 (2^20)
bytes (approx. 1 million bytes)
- 1 gigabyte = 1 Gbyte = 1,024 Mbytes = 1,073,741,824 (2^30)
bytes (approx. 1 billion bytes)
- Number of bits that can be held by registers and processed
as a single unit.
- Size of the word affects the processing speed of the computer.
- Mainframes typically use 32 - 64 bit words.
- Minicomputers usually use 32 bit words.
- PCs use 8 - 64 bit words.
- Define which set of bits is equivalent to which character
of data.
- ASCII (American Standard Code for Information Interchange)
- EBCDIC (Extended Binary Coded Decimal Interchange Code)
- American Standard Code for Information Interchange
- Common on PCs
- Uses 7 bits to represent each character
- "A" = 1000001
- Extended Binary Coded Decimal Interchange Code
- Used on IBM mainframes
- Uses 8 bits to represent each character
- "A" = 11000001
- Microprocessors usually contain four key components
- Control Unit and Arithmetic/Logic Unit
- Registers
- Buses
- Clock
- Silicon chips, which can be smaller than a thumbnail
- Non-volatile - remains after computer is turned off.
- Provides computer with instructions during booting.
- Store firmware programs.
- Volatile - information is lost when computer is turned off.
- Accessed by user for writing programs or storing data and
software.
- 2 types: dynamic (DRAM) & static (SRAM) - static is faster
but more expensive.
- Part of RAM can be used for caching - data & instructions
placed here prior to being needed by CPU.
- User programs instructions into chip - once programmed, can't
be changed.
- Useful for special purpose computers.
- Collections of wires used for communication among CU, ALU,
& memory.
- The bus size is usually related to the word size.
Parallel Processing
- Two or more processors, each with their own memory units work
at the same time.
- Eliminates serial processing bottleneck on single processor
CPUs.
- Parallel processors are starting to appear on some high end
computers.