CS224 COMPUTER ARCHITECURE AND ORGANIZATION
Review of Computer Systems :
The Evolution of Computers
Development of the technologies used to fabricate the processors, memories and I/O units of computers has been divided into four generations:
1st Generation (1945-1955) :
o Vacuum tubes were used to perform logic operations and to store data.
o The key concept of a stored program was introduced by John Von Neumann.
o Programs and their data were located in the same memory, as they are today
o Assembly language was used to prepare programs and was translated into machine language for execution
o Basic arithmetic operations were performed in a few milliseconds using vacuum tube technology to implement logic functions.
o This provided 100- to 1000- fold increase in speed relative to the earlier mechanical and relay based electro mechanical technology.
o Mercury delay – line memory was used at first, and I/O functions were performed by devices similar to type writers.
o Magnetic core memories and magnetic tape storage devices were also developed.
2nd Generation (1955-1965):
o Transistor was invented at AT&T Bell Laboratories
o Magnetic core memories and magnetic drum storage devices were used
o High level languages, such as Fortran was developed, making the preparation of application programs much easier
o System programs called compilers were developed to translate these high-level language programs into the corresponding assembly language program, which was then translated into the executable machine language form.
o Separate I/O processors were developed that could operate in parallel with the central processor that executed programs, thus improved overall performance.
3rd Generation (1965-1975):
o IC (Integrated Circuit) Technology was introduced where the many transistors were fabricated on a single silicon chip
o IC memories replaced magnetic core memories
o Other developments included the introduction of microprogramming, parallelism, and pipelining.
o Operating system software allowed efficient sharing of computer system by several user programs.
o Cache and Virtual memories were developed
o Cache memory makes the main memory appear faster than it really is
o Virtual memory makes it appear larger
o System 360 mainframe computers from IBM and the line of PDP minicomputers from Digital Equipment Corporation were dominant commercial products of the third generation.
4th Generation (1975 to Present):
o Very Large Scale Integrated (VLSI) Technology allowed a complete processor to be fabricated on a single chip is microprocessor. Intel Company played major role.
o Organizational concepts such as concurrency, pipelining, caches and virtual memories evolved to produce the high-performance computing systems
o Portable notebook computers, desktop personal computers and workstations, interconnected by LAN, WAN and Internet have become dominant mode of computing.
