lote 
rom 
ric 
| to 
rge 
of 
of 
lal 
S. 
are 
lar 
any 
. by 
ies 
eir 
MS. 
eir 
es: 
out 
was 
had 
mer 
be 
sed 
of 
uch 
and 
age 
ers 
ls. 
red 
his program through punched cards or paper tape and controlled its operation 
through console switches. Debugging was performed by single-stepping through 
the program and watching the console lights and changing individual bits in 
the program. Once the program was working and operational, trained operators 
loaded the programs one at a time and mounted cards or tapes to provide the 
data. The programs were run in a batch stream, one after the other. The 
concepts of operating system and interactive user interface were 
non-existent. 
Stage II: 31965-1985 
In time, symbolic assemblers were developed to convert mnemonic codes and 
labels to machine code, and later high level languages were developed to 
convert mathematical expressions into the language of the computer. As 
computers became more sophisticated and popular, a profession that once 
consisted entirely of scientists and engineers began attracting eager but 
less computer-knowledgeable people. A buffer was needed between this new 
breed of programmer and the machine. Also, to improve the efficiency of 
resource utilization, it became desirable to handle more than one job at a 
time. The process of assigning each job a specific amount of time, during 
which it had total control of all the computer system resources, was no 
longer effective as the systems became larger. Thus was born the executive, 
or master program, to schedule jobs and to mediate among jobs contending for 
resources. Next, the operating system evolved, together with libraries of 
control and communication instruction sets, utility programs and development 
tools. 
The application programmer no longer had to worry about the details of 
input/output or the scheduling of resources. He did not really have software 
portability, as the utilities and operating system features were (and still 
are) largely vendor-specific. A degree of "upward compatibility" was 
provided to enable a given application to operate on the newer, more powerful 
computers introduced by each vendor. Proprietary operating systems are still 
the order of the day. Although UNIX continues to gain popularity, especially 
in academic circles, there is still no single standard. Thus, users are 
encouraged to purchase ever more powerful machines without having to rewrite 
their software, provided they stay with a particular hardware manufacturer. 
Stage III: 1985- 
In the past, most organizations using computers found it relatively easy to 
make a central decision on which manufacturer's equipment to buy. The choice 
of manufacturers may not have been easy, but the need to make the decision 
centrally was clear. Computers were big and expensive, required extensive 
internal support and ran a limited, well-defined set of applications. Nov, 
computers are smaller, less expensive, more powerful, more flexible and more 
functional. 
Large mainframes will continue to be needed as network controllers, central 
database | managers and superproblem solvers. However, there is some 
displacement taking place by networks of personal computers. It is no longer 
uncommon to find a netvork of hundreds of PCs served by a single large disk 
for storage and a few central printers for output. 
Today the industry is obsessed with the ideas of "user friendliness" and 
"industry compatibility". It is becoming increasingly important that 
software products be easy to learn without the need for instruction beyond 
that contained in the manuals supplied with the software. Moreover, it is 
more important than ever for software to run on as many computers as 
593