1950 to 1959: Starting the Ascent of Digital Computers and Software - The Technical and Social History of Software Engineering - page 89

also dozens of ALGOL-like languages based on some of the defined features, such
as SIMULA.
Early computers were coded in machine language , which is so highly complex
that errors were rampant and hard to find and fix. Assembly languages introduced
mnemonic source instructions that were somewhat easier to understand than bin-
ary numbers or machine language.
Originally, assembly languages had a one-to-one correspondence with machine
languages in that each source statement was translated into a single machine in-
struction. Later, the concept of macro-assembly languages expanded the scope of
assembly source-code statements.
A macro instruction was a method that allowed a number of statements to be
created and named separately. The collected statements were called macros ; a
macro instruction is still a quick way of adding reusable features to an application.
The First Commercial Computers
A commercial computer is a computer that is built specifically to be sold or leased
to paying customers rather than for internal use within the organization that built
it.
The history of early commercial computers is ambiguous and confusing when
you try to pin down who developed the first commercial computer. The U.S. his-
torical literature claims that the UNIVAC I was the first commercial computer
sold to paying clients. Some U.K. literature claims that the LEO I computer was
delivered a month prior to the UNIVAC I. Another British machine, the Ferranti
Mark I, also claims to have been delivered before UNIVAC I.
Table 4.1 shows the delivery dates of early digital computers.
Table 4.1 Early Digital Computer Delivery Dates
Regardless of who built the first commercial digital computer, the idea of com-
puting as a business tool was rapidly expanding. There would soon be dozens of