Simple model of a computer

Answer 1

A computer system can be divided into 5 components:

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 InterfaceExternal Bus Structurecollection of "wires" that carries power and signals between different computer componentsChannelseparate, special purpose IO processor connecting an IO device to the CPU (or "main memory"); may perform signal conversion, timing control, buffering, etc.Communicationsdirect/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 cellseach containing a binary patternunits:byte(typically 8 "bits") - characterword(typically 32 "bits" but many different sizes are found on different computer systems) - basic numeric unit; basic unit of data transferKbytes210 bytes (1024)Mbytes220 bytes (1,048,576)Gbytes230 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. ROMROM 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)
• REGISTERSMAIN MEMORYSECONDARY STORAGESPEEDvery fastfastslowDURATIONvery short-termshort-term (while program is active)long-termPOWER DOWN EFFECTdata lostRAM- data lost; ROM - data maintainedmaintainedSIZE OF UNIT TRANSFERREDbit, byte, or wordbyte or wordphysical record most commonALU ACCESSyesindirect onlyno

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)

DataOne of the major requirements of any computer system is the ability to represent and manipulate values ("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. InformationTwo terms common in any discussion of computer systems are "data" and "information". The difference in meaning between these two terms is based on the concept that "information" is "data" which has "meaning" to someone (or something) outside of the computer system.

"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) ModelA computer system can be thought of as a collection of components which together are capable of 3 operations: Input, Processing, and Output. A fourth operation, Storage, is also required for practical computer systems.

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:A computer system must include a method for accepting "data" and "instructions" from outside the system.

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

Processing:A computer system must include the ability to change or "transform" data which has been input. These "transformations" typically include (but are not limited to)

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

Output:A computer system must include the ability to send processed data to outside the system in a form that can be used by the "outside world". This "outside world" might be the human "users" of the computer system, but alternatively could be electrical or mechanical controls for automated equipment, or the "inputs" for some other system. Storage:We would not normally consider a collection to be a computer system unless it included some form of memory of previous input or processed data. For example, system composed of an electrical power supply, an on/off switch, a light bulb, and appropriate wiring to connect the other three components would not normally be considered to be a computer system (although it contains IPO elements of a basic form). Replacing the on/off switch with a "toggle button", which would reverse the current on/off "state" of the light, would give us something closer to a computer system.

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