Early Experiences in Computing

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Anyway back to computers. The computer being developed by BTM was called The HEC

The HEC
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A later version of the HEC
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which was a First Generation Computer. Like all computers it had to be programmed, but programming was then as much an art as a science. The machine basically comprised of a Programme Controller and Arithmetic Unit (the CPU) and Storage in the form of a Magnetic Drum (the Drum).

Remember this was before the days of Solid State storage and the modern RAM. The Drum was divided into 64 Tracks each consisting of 16 words. Each of the 1024 words consisted of 40 binary bits, holding either Instructions or Data. All programming was in the form of a Binary Machine Code, no high level languages existed.

Execution of a program consisted of reading an Instruction from the Drum into the CPU, executing the Instruction which then consist of reading Data from the Drum. The Data was then processed before being written back to the Drum. Finally part of the Instruction contained the address of the next Instruction which was then read from the Drum.

At all times the programmer had to remember the addresses of where data and instructions were stored. A further point to remember is that the Drum is a mechanical device rotating at a relatively slow speed so it might take up to a full revolution before the required address passed the reading heads and the required Instruction/Data was read. As the rotational speed of the drum was fixed it was known how long it took for each address to be read, also it was defined how long each instruction type took to execute.

To optimum programming the machine, it was ideal if at a given instant the programmer knew exactly where, in it's rotation, the drum was so that he could ensure that Instruction or Data required was about to pass under the read heads. If you can imagine the surface of the Drum, it would consist of Instructions and Data scattered all over it's surface. Instructions and Data were stored in pure binary Data having been converted during input while Instructions were input as Binary. An Instruction would consist of : Operand address, Function to be performed and the Next Instruction address.

Data and Instructions were input from Punched Cards and Final results could be either Punched out on new cards or Printed on the integral Printer.

Apart from Computers, the company also manufactured Electronic Calculators,

A 541 Calculator
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still based on Thermionic Valves. These were machines that would read a Punched Card (at 100 cards per minute) containing Data, perform a calculation on the Data and Punch the answer back onto the same Punched Card. Data was handled in the form of 'Bini Ten' which meant that each digit was stored occupying four bits rather like Hexadecimal but instead of a single stream of bits there were four streams running in parallel round the machine.

The Author working on 541
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These four streams allowed handling sterling money values with 12 pennies = 1 shilling and two 10 shillings = 1 pound. The earlier versions were very simple only allowing multiplication on an input Multiplier and Multiplicand arriving at a Product.

The 550 Development Team
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This was achieved with three registers, but later versions had more than three registers allowing carry over or accumulations from successive Punched Cards.

The 550 Calculator
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The 555 Calculator
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The latest version of this machine had a Magnetic Drum for Data storage. Programming of Calculators was in the form of Plug Boards.

A Plug Board
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A Plug Board was a form of patch panel where each step of a program was defined by inserting plug links. There would be a different Plug Board for each application performed and changing an application just required inserting different Plug Boards.

At this point I will dwell on a contention that existed on the definition of a Computer. A Computer was defined as a machine that could modify it's operation based on the results of previous operations within the Program. This is an ability to make a Decision. In a stored program computer this can be achieved by changing an instruction i.e. writing a modified instruction into the programme. In the case of the latest Calculator, where the instructions were pre-set by the Plugboard, it was impossible to change this. All that could be done was to select a different set of instructions which had been already defined. Still this is a form of decision making.

In the late 1950s transistors came on the scene which resulted in the Second Generation Computers. The machine I was personally concerned with was known as the 1300 Series.

The 1300 Computer
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This was much larger, physically, than the HEC and required a very large room dedicated for it. Apart from an enlarged Magnetic Drum there was a RAM in the form of a Core Store and Magnetic Tape Storage which greatly increased the storage capacity. This machine also ran in the 'Bini Ten' mode. Input was by Punched Cards (now running at 600 cards per minute) and Paper Tape was added as a later option. By modern standards the internal storage capacity was tiny. The Drum held 12,000 words, each bank of Core Store held 400 words, there could be up to 5 banks. Magnetic Tape capacity was prodigious a reel being up to 3,600 feet long and there could be up to eight Tape Decks. Programming now used moved into the realm of high level languages and one of the earliest available was Cobol. There were 200 of these machines built and they found there way into Large Companies and Public Utilities. The reason for the demise of this particular machine was purely technological advance and the development of Integrated Circuits.

The next series of Computers I was concerned with was known as the 1900 Series.

A 1900 Computer
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This was still physically large but comprised of a number of individual units which were only connected by cables compared with the 1300 which was bolted together as one central mass. The 1900 Series used Octal as the internal method of holding data. Programs were usually input in the form of Paper Tape whilst Data was normally on Punched Cards. High level languages available included Cobol, Fortran, Pascal amongst others and programming became more of what we now know. Operating Systems came into use i.e. George III, and the machine was able to run more than one program at once using resource sharing. A Standard Interface was developed allowing a mix of peripherals

A 1900 Computer
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with a minimum of program changes.

As time progressed successive machines were introduced becoming physically smaller while the capacity and speed increased. The machines were still known as Mainframes as they are still known today.

Up to 1975 I had been concerned primarily with designing, building and maintaining machines, but at this point I moved onto system design, analysis and programming. An area I stayed in until I retired in 1995.

In the late 1970s the PC as we know it came on the scene. The first machine I had was a SWTP6800. This was based on the Motorola 6800 and came in the form of a kit. For input/output I used a Teletype as no Video was available. This machine had a Basic Interpreter program and was my first association with this language. Then the Commodore PET 2001 came on the scene, I still have mine be it tucked away in the Garage. We all know the Commodore story from then on so I will not dwell in this area. ICL produced it's first PC, be it based on the RAIR Black Box, which used C/PM.

By this time I had become a Home Worker i.e. I no longer had to travel to work, only go to my office in my house. Maybe I even had the privilege of programming your Poll Tax or Rates. Programming then consisted of writing programmes on coding sheets, sending the sheets to a site for punching on cards or paper tape and subsequent running on a Mainframe. The result of the run then being posted back to me. It was also possible to dial-in to a mainframe using a Typewriter type terminal with built in Acoustic Coupler. Speeds were only up to 300 baud and line interference could be a problem resulting in loss of connection.

The PC brought the power of the Mainframe back to the Desktop and, as they say, the rest is history.

To summarise, during my 40 plus years in computing I have seen an industry grow from a fledgeling into one that now touches all aspects of life and we could not do without it. I have seen electronics grow from large Thermionic Valves with their high voltages and power requirements to devices with almost unlimited capacity running on a button battery. I have travelled and been able to see the most intimate side of business, and if I had my time again I would not change a thing.

If any readers have had associations with these machines I would like to hear from them. Also if they would like to know more please don't hesitate to contact me. I can be reached at: francis.townsend@bigfoot.com and I have a Home Page (be it simple) at: http://www.ftownsend.freeserve.co.uk

Happy computing to you all.