1. Basic Computer Architecture Models

The 5 Component Model

1. Hardware
2. Software
3. Data
4. Procedures
5. Personnel

In studying Computer Systems' Architecture, only the first 3 of these are of direct interest.

Hardware

• Processor
  • a.k.a. CPU / Central Processing Unit
  • Components:
    1. ALU / Arithmetic Logic Unit: arithmetic & Boolean logic operations
    2. CU / Control Unit: instruction processing sequencing and control
    3. Interface Unit: (internal) bus structure
  • Alternate View
    1. Execution Unit: instruction circuits (including ALU)
    2. Control Unit: instruction retrieval, sequencing, and EU sub-circuit selection
    3. Registers: limited, quick-access data "containers" and "flags"
    4. Internal Bus Interface
• Input & Output Devices
  • Actual electrical or electro-mechanical IO devices (e.g. keyboards, printers, video monitor) will not be considered as significant in our study of Computer Systems' Architectures.
• Input & Output Interface

  External Bus Structure

  collection of "wires" that carries power and signals between different computer components

  Channel

  separate, special purpose IO processor connecting an IO device to the CPU (or "main memory"); may perform signal conversion, timing control, buffering, etc.

  Communications

  direct/indirect connection to other computer systems based on pre-agreed upon "protocol" (shared rules for how communication is to take place

• Storage / Memory
• (Main) Memory / Primary Storage

  addressed cells

  each containing a binary pattern

  units:

  byte

  (typically 8 "bits") - character

  word

  (typically 32 "bits" but many different sizes are found on different computer systems) - basic numeric unit; basic unit of data transfer

  Kbytes

  2¹⁰ bytes (1024)

  Mbytes

  2²⁰ bytes (1,048,576)

  Gbytes

  2³⁰ bytes (1,300,109,824)

  usage:

  • "active" data and instructions (i.e. instructions and data currently being processed
  • John vonNeumann & stored program concept vs. Babbage's engine with separate data and instruction stores

  RAM vs. ROM

  ROM is non-modifiable (by normal computer operation)

• (Secondary) Storage
  • long-term (inactive) data and program storage
  • examples: disk, tape, CD
  • units: typically stored in "blocks" of multiple words/bytes (physical records)

• 	REGISTERS	MAIN MEMORY	SECONDARY STORAGE
  SPEED	very fast	fast	slow
  DURATION	very short-term	short-term (while program is active)	long-term
  POWER DOWN EFFECT	data lost	RAM- data lost; ROM - data maintained	maintained
  SIZE OF UNIT TRANSFERRED	bit, byte, or word	byte or word	physical record most common
  ALU ACCESS	yes	indirect only	no

Software

• System Software
  • Operating System
  • Utilities (may be built into OS or external programs)
• Application Software
  • Application tools: word processors, spreadsheet managers, etc.
  • Corporate applications: in-house systems e.g. inventory management
• High-level vs. Machine-level Software
  • High-level: "source" instructions in a language such as COBOL
  • Machine-level: binary patterns with no immediate human meaning
  • High-level instructions must be converted into Machine-level instructions before they can be processed by a "processor"; this conversion is a one-to-many process
• Instruction Classes
  • data transfer (copying data)
  • data transform (modifying data)
  • instruction flow control (changing the default sequence)

Data

In general, digital computers (the only type considered in this course) represent values as patterns of "off" and "on" signals. Each value requires a different pattern (or, at least, a pattern which is different from any other value of the same type). Different types of values generally are represented using different "encoding schemes". An "encoding scheme" specifies how many "off" and "on" signals are required for each value, and provides a unique pattern of signals for each possible value.

Data vs. Information

"Information" is "data" which has meaning. The most common task of a computer system (especially when the input source and the output destination are the same) is to transform data into information. In fact, this is sometimes used as the basis for alternative definitions of a computer system .

The concept of "meaning" can be difficult. Generally, we think of "meaning" as implying that something with intelligence exists for which the "data" has meaning. When the output of a computer system is the automated control of some other system (as in CAD, Computer Aided Manufacturing), we end up debating, the unresolved question of what is meant by "intelligence".

1. The IPO(S) Model

Note that the IPO(S), Input-Process-Output(-Storage), model is applied to at least two different areas:

1. the collection of "equipment" that makes up a computer system
2. the "actions" that a computer system is capable of performing.

Input:

Power or energy sources required to enable operation of the computer system are not "inputs".

Processing:

• selecting subsets of the data
• counting and accumulating totals of selected data values
• re-arranging the sequence or "format" of data

Output:

Storage:

For the purposes of this course memory (or "storage") will be considered to be an essential element of any computer system.