A11-A SIMPLE DESCRIPTION OF MINI--THE PDP SERIES OF SMALL COMPUTERS

 

By    pragyansharma polavarapu 

 (A)INTRODUCTION

(1)The  MINI computers of 1960s and 1970s were  really  very small  compared to the old giant electronic calculating machines like ENIAC of 1940s . The old electronic  calculator-computer machines like the respected ENIAC   were of the size of  big halls in houses. Wonder of wonders,the MINIs  of 1960 and 1970s became reduced to the  size of  just  table-top band radios! The transformation was made possible solely after the discovery of  tiny sand particle-sized  “TRANSISTOR” (silicon triode) and its use  in the MINIs .  Hundreds or even thousands  of transistor  triodes were used in creation of  hundreds of logic circuits in registers and processors inside the computer.

(2)The transistor was invented in 1947 after a series of researches on tiny “crystal diodes” made from semiconductor materials like Germanium and Silicon (both non-metallic elements). The first  transistors were junction diodes, created by joining  “doped” p-type and n-type semiconductor wafers. Doping means entering atoms of other selected elements into crystal lattice structure of Germanium/Silicon by a carefully controlled accurate chemical/physical processes.  Doped silicon wafers of n-type have excess electrons . Doped silicon wafers of p-type are dificient in electrons. Joining of the p-type and n-type materials  creates  triodes. They are   of extremely minute size(of the size of sand particles or even smaller )  compared to the huge triodes created with “thermionic tubes”. The thermionic triodes used in old computers of 1940s were of the size of electric bulbs and made the old computers to be of a house size.  The less than sand grain sized transistors used in MINIS performed more efficiently than the thermionic tube triodes.

(3)The MINI computers of 1960s started using the   transistor triodes and created the “MINI  computer revolution” . The MINIs  were  popular  for about three decades  in period 1960 to 1980s .But they too were  costly at about 20,000 dollars and were not within reach of common people.

 (4)In one respect the mini can be compared to  a big mansion  of say  fifty  rooms. Just as the  mansion  is constructed out of tiny  bricks, a computer’s digital brain  is also constructed using hundreds of thousands (now millions) of  tiny sub microscopic “electronic bricks” called transistors. The first single transistors were rigidly fixed in tiny  glass jackets and dozens of them  rigidly fixed on Bakelite boards in  electric circuit diagrams and connected by hair thin metal lines printed on the Bakelite boards . This technology  of wiring the  logic circuits with transistors on Bakelite boards later developed in to 50 to 60 billion worth multi-layered highly sophisticated”printed circuit board”(PCB) technology.

 (5)As  already said the MINI   computer  came in the  size of an old multiband  table radio . It has a small processing unit containing many inter-connected tiny PCBs containing assemblies of thousands of transistor triodes.such a processing unit (equivalent to ----of modern desktop computer )was roughly of size of a modern fritz. The MINI had  also a  key board like that of  type writer to directly type “software instructions”(commands to computer’s digital brain given in a highly developed mathematics based software language) . One small room with a table and chair was sufficient.

(6)Inside  the MINI  computer, the software architecture and  engineering plan  was  almost exactly the same  as in the  standard IAS architecture of the ENIAC of 1940s . The   MINI  computers which appeared in 1960s looked very sophisticated and appeared to be pointing to a new computer era. The MINIs  were used only by senior engineers mainly for  remotely controlling chemical  and industrial processes.

 (7) the first MINI s made of transistor circuits---,like the  PDP-8 series  poroduced by DE corporation---were   a thousand times  more powerful than  the old computers of  of 1940s. Compared to price of one million dollars for the giant size machines like ENIAC  and  EDVAC, the  PDP-8  machines were priced at around 20,000 dollars!  The later PDP models  costed only around 5000-6000 dollars ! The first pdp-8 with its  related  electronic parts weighed only about 100 kg while some later models weighed much lower ,some weighing only about 25 kg! The MINI, in a compact beautiful size fitting into a researcher’s room, created a technical revolution and most surely also  an intellectual  revolution.  Scientists and engineers were excited  about the  technical potentialities of the radio-size new wonder machine called  computer  .

 

(8) The primary software plan and architecture  of   electronic calculating machine (the IAS  model) was  invented while creating the ENIAC of 1940s. Since then this standard technical  plan is implemented  in all the hundreds of millions of computers  even of today.

( B )OTHER  FEATURES

(1)But the most wonderful development in computer technology , developed by the  MINI   computers was “interactive computing”. It is a great revolutionary idea , next only to the  “IAS architecture” of 1940s mentioned above.  

“Interactive computing”  turned the MINI  computer into a truly magical  machine with a robot brain and  greatly popularized computer among engineers.Two MINI computers, connected through a communication channel ,could interact like friends. Each  could act independently  and interact with the other computer.

(2)The most important  condition for Interactive computing is that  a live  “FEEDBACK LOOP” for communication between the computers should exist . It can be a series of software command loops or  some extra hardware . Sensors in  each of the interacting computers  awaken the other computer to particular tasks. This technology perhaps led to the development of “CLIENT-SERVER” type  software. Among two computers ,one   would first create  an “output data” for  the other computer. The receiving  computer analyses the  data received by it and instantly  creates a new  output and send to the first computer.Such interactive sessions would continue as long as necessary.

(3) In 1960s the  most useful  “CLIENT-SERVER TECHNOLOGY” was  developed  perhaps based on the principle of interactivecomputing.  Many users could simultaneously utilize the  same mainframe computer by a procedure  called “TIME SHARING”.

We know that  a computer does logical and mathematical work in millionth of second units .For  a  computer,a “second” could be divided in to several hundred pieces each containing a tiny   “time slice”. For  humans such “time slice” may be unmanageably small ,but it is big for the computer’s CPU which works in millionth of second units .  It is a big time slice.  A few such time slices are  alloted  to each human user . Each user’s quota of time  gets repeated thousands of times in each second and he even feels that he is the only person utilizing the entire time of the  “SERVER” (the chief central computer). The client/server environment  is also type of  interactive computing .

( 4 ) Perhaps, only after the idea of “interactive computing” became popular in  MINI s, other great technologies like MSDOS,  WINDOWS ,WORD PROCESSING , ICON  based computing (using MOUSE and DIALOGUE BOXES  ) etc were developed. The basic idea under all such technologies is existence of a  “feedback loop” to convey data signals to both the interacting computers. This means that one computer’s output influences “next action”  in the other  computer and creates the feeling that both computers,like humans, are able to converse.

( 5 ) In modern days the  special highly standardized  codes  called  “SOFTWARE LANGUAGES” are used to send commands to the digital brain of computer. Various software languages like FORTRAN, BASIC ,COBOL were developed. These languages with their RESERVED WORDS  are in advance loaded in the  computer and managed the entire working of the computer  most accurately. 

The old software languages like BASIC and COBOL construct software programs resembling  single room houses .The  modern soft ware languages like C  and JAVA can construct  programs resembling strong multistoried houses(STRUCTURED PROGRAMMING). Languages like C ⁺⁺,JAVA ⁺⁺ are far more stronger like engineers using new machinery and new techniques  to construct still bigger houses.

(6)In radio or television,after  we hear/see a program the program  simply “evaporates into thin air”and disappears without trace like water flowing out of an open pipe . But in computer  a  program (text file, picture file,sound file,video file ) after they are read/seen/heard by us are  stored not just for hours and days but even years. They are stored in computer’s files and do not  disappear until we erase them .

MISCELLANEOUS

(1)Several models   named PDP-8/S, PDP-11,PDP-12,PDP-14 etc were released . Each new model had some new facility perhaps suited for a  particular groups of users. It is said that about 300,000 PDP machines were sold . This indicated that the PDP machines were useful  for various types of commercial/scientific/technical/ data processing  purposes.

 (2)The most important point is that with the availability of a small tabletop computer of the size of a old valve radio, further research about many potentialities small computer got accelerated. Small  networked computer systems appeared for interactive use in many fields of science  and inaugurated  the dawn of  the modern era of IT as we see today.

(3) In the early MINI  computers the magnetic and other data storage devices could store only small quantities of data . But they were really pathways to great research in computer theory.  “Magnetic core memories”  made of thousands of extremely small  magnetized  ferrite rings 1.5 mm to 2.5 mm in diameter were interconnected  through hair thin wire paths/printed metal lines etc . The magnetic rings were arranged in vertical/horizontal rows with switch on/switch off facilities.

 (4)Later  large storage devices like magnetic tapes  and optical discs were created. The technology of converting text data/picture data and sound data into digital  strings of billions of 0s and 1s was  invented.  In modern computers such huge data is nowadays stored in button size computer chips  containing hundreds of millions of transistor storage units (flash memories).Whole books (thousands of pages),whole  photo albums can be  stored. Even entire  videos and commercial films are stored in such digital storage devices.