1.6. Read and translate the text the minicomputer as a control component

Since the beginning of the sixties one has become ac­customed to phenomenal growth in general-purpose digital computers as each year has brought in more powerful and larger systems. These general-purpose data processing ma­chines have required special environmental conditions, large operational and support teams¹ and special maintenance. During the same period, a rather curious development has taken place in the small computer field where machines have been getting smaller in size with improved perform­ance at steadily declining costs. Today such machines, al­though identical in basic concept, are named "minicom­puters" to differentiate them from their big brothers. The "mini" can be plugged into a 13 A point,² placed on a table in the corner of a laboratory and is accessible to anyone with zeal to learn a relatively simple programming language and typing. The steady trend in lower cost, smaller size, higher reliability machines backed up by sophisticated pe­ripherals and software is opening up new application areas undreamt before. We are now observing an exciting period in this field, as new components and technologies are rap­idly finding their way into minicomputer construction -and almost every month, a new development is announced.

Minicomputers first appeared about the beginning of the sixties. Their progress followed closely the development of digital circuit technology. First transistors, then inte­grated circuits and now M.S.I.³ and L.S.I.⁴ circuits are being used in their construction.

The minicomputer applications cover a wide range such as — industry, telecommunications, business, laboratory, and other applications.

It is not easy to define a minicomputer on the basis of its construction principle or performance. Regardless of the diminutive title, its computational power is by no means negligible; in fact, in some respects it is superior to the large-scale general-purpose computer. For example, many mi­nicomputers have considerably higher peripheral transfer rates.

1.7. Read and translate the text programs and algorithms

The computer is required to manipulate data in accor­dance to some desired specification. The set of rules of manipulation the equations, both arithmetical and logical, which the machine performs is often called an algorithm. This al­gorithm is "programmed" into the machine. There are a num­ber of levels of computer programming, ranging from the basic (binary) instructions which organize the machine to "high level" language such as FORTRAN. High level languages are English like and therefore much simpler to write; such programs are then converted (by processing in the computer) to an appropriate set of machine code in­structions.

In general the computer is so fast that it can process a number of algorithms by time multiplexing, i.e. more than one D.D.C.¹ loop can be closed. The second D.D.C. can thus be performed in time sequence. This multiplexing will be controlled by the computer program.

Hardware and Software

The basic electronic components that go to make up a computer are called the "hardware". The set of instructions to be performed by the machine, i.e. the programs, is termed the "software". Many tasks can be performed by either hardware or software. For example multiplication can be performed by repeated additions using the hardware addi­tion facility fundamental to all machines; this is under con­trol of a special program and is therefore a software method of multiplication. On the other hand a special electronic multiplier unit can be added to the machine to perform hard­ware multiplication. The hardware device is much faster but also more expensive!

Minicomputers Versus Special Purpose Devices

The basic design problem can often be solved by using a computer, but has more often in the past been solved by using specifically developed special purpose devices. This approach was most reasonable because of the high price of computers, but is no longer such a valid argument.

What advantage is there in using a computer? The answer is quite simple: flexibility. At the design stage of a piece of equipment the specification is set for the controller (using the word loosely). When the specification is commissioned this may be alright but most likely would be bet­ter if modified. But modifications to special purpose machinery are expensive! Not so using a computer; one merely has to change the program — not the hardware at all! It does in fact mean that development of the controller can move along with developments and new requirements in the overall system — it is common initially to program only for a basic minimum requirement and to develop from there. This flexibility available through the media of changing the program, which can be "loaded" in minutes normally, means that the same computer can be used to do another completely different work schedule when it is not being used for the job it was primarily intended for. This would seldom happen in a dedicated industrial system, but may well occur in research and development departments. In this sense the "mini" can be claimed to be a general purpose machine, but this is not the usual sense of the phrase applied to com­puters.