Disappointment with Wiki made me Blog

Wikipedia is a place of knowledge. Got disappointed when I went there I for a definition in the Glossary of Computer Hardware Terms. Noticed some definitions vague. Some confusing. Some inaccurate. Some misleading. Some wrong! As I did in the year 1988, I noticed another opportunity for me.

Having authored two Computer books, one for Hardware Engineers and another for Graduate Students of Computer Science, I decided not to go back. Let me do something for School Children. Provide simple definitions for often used Basic computer terms that are useful for non-IT Professionals and laymen too.

1. BUS CONCEPT 

What is a BUS ? Often many persons give vague definitions. 

1.0 I/O BUS in Mainframe Computers

In the year 1973, I asked this question to my boss, Late Prof. J R Isaac at IIT Mumbai. He took me near the main frame computer, EC-1030, IBM System 360 compatible mainframe computer. Opened the doors of I/O Channels frame (Shelf). He defined the Standard Input / Output BUS between the Data Channel and the I/O Controller.

He showed the physical aspect of the BUS: "A huge, thick bunch of cables carrying about 34 signals between the I/O Channel cabinet and the I/O Controllers.  The signals through these cables form the standard I/O Interface." 

These signals were of different types:

 1. OUT Data signals (Device Address / Command / Data) from the Channel to I/O Controllers, 

2. IN Data Signals (Device Address, Data and Status) from the I/O controllers to the Channel, 

3.Flags (READY, REQUEST, ADDRESS AVAILABLE, COMMAND AVAILABLE, DATA AVAILABLE, STATUS AVAILABLE etc.) 

4. Select lines, 

5.Power 

and 6.Ground.

The EC-1030 is a 32-bit main frame similar to IBM System 360/40. It had 32-bit adder. The I/O Bus had 8-bits for OUT data and 8-lines for IN Data.  

1.2 BUS Concept in Mini Computers

In 1991, In my first book, "IBM PC AND CLONES", I defined the BUS as a feature introduced in mini computers. "The bus concept for communication between CPU and all other units in a minicomputer " reduces cost.

1.3 BUS in Micro Computers

In 2004, In my second book, Computer Architecture and Organization, I defined the bus as: "In mini computers and micro computers, bus is a shared common path for several sources and destinations".

1.4 COMMON PRACTICE

In mainframes, there used to be several, multiple paths that are dedicated for Data, Address, Status, Command etc. Hence more wires, more circuits for drivers and receivers. Hence high cost. In mini computers, the bus is a link for communication between the functional units: CPU, Memory, I/O Controllers. In micro computers, there is an internal bus and external bus. Popular Computer Bus types are VME Bus, ISA, EISA, PCI etc.

1.5 CONCLUSION

 "A BUS is a common path shared by multiple subsystems or components to send / receive signals." 

When we say 8-bit Data Bus, we mean there are 8 buses for 8 data bits. In other words, each dat bit is a bus.  For each bus signal, there will be a driver circuit at the sending end and receiver / buffer circuit at the receiving end.