It is hard to say exactly when the modern computer was invented. Starting in the 1930s and through the 1940s， a number of machines were developed that were like computers. But most of these machines did not have all the characteristics that we associate with computers today. These characteristics are that the machine is electronic， that it has a stored program， and that it is general purpose.
Perhaps the most influential① of the early computer-like devices was the Electronic Numerical Integrator and Computer， or ENIAC. It was developed by J. Presper Eckert and John Mauchly at the University of Pennsylvania. The project began in 1943 and was completed in 1946. The machine was huge； it weighed 30 tons and contained over 18，000 vacuum tubes.
First-generation computers were characterized by the use of vacuum② tubes as their principal electronic component. Vacuum tubes are bulky and produce a lot of heat， so first-generation computers were large and required extensive air conditioning to keep them cool. In addition， because vacuum tubes do not operate very fast， these computers were relatively slow.
Other software developments during the first computer generation include the design of the FORTRAN programming language in 1957. This language became the first widely used high-level language. Also， the first simple operating systems became available with first-generation computers.
In the second generation of computers， transistors replaced vacuum tubes. Although invented in 1948， the first all-transistor computer did not become available until 1959. Transistors are smaller and less expensive than vacuum tubes， and they operate faster and produce less heat. Hence， with second-generation computers， the size and cost of computers decreased， their speed increased， and their air-conditioning needs were reduced.
Many companies that had not previously③ sold computer entered the industry with the second generation. One of these companies that still makes computers is Control Data Corporation (CDC). They were noted for making high-speed computers for scientific work.
The technical development that marks the third generation of computers is the use of integrated circuits or ICs in computers. An integrated circuit is a piece of silicon (a chip) containing numerous transistors. One IC replaces many transistors in a computer； result in a continuation④ of the trends begun in the second generation. These trends include reduced size， reduced cost， increased speed， and reduced need for air conditioning.
The fourth generation of computers is more difficult to define than the other three generations. This generation is characterized by more and more transistors being contained on a silicon chip. First there was Large Scale Integration (LSI)， with hundreds and thousands of transistors per chip， then came Very Large Scale Integration (VLSI)， with tens of thousands and hundreds of thousands of transistors. The trend continues today.
We may have defined our last generation of computers and begun the era of generationless computers. Even though computer manufacturers talk of “fifth” and “sixth”-generation computers， this talk is more a marketing play than a reflection of reality.
Advocates of the concept of generationless computers say that even though technological innovations⑤ are coming in rapid succession， no single innovation is， or will be， significant enough to characterize another generation of computers.
Some idea of what might be happening in the near future in supercomputer design can be gleaned⑥ from a press release issued by the US Department of Energy (DoE). It came out of the SUPERCOMPUTING 2002 Conference held last November in Baltimore， MD. The press release announced that the DoE had awarded IBM a 290 (USD) million contract to build the two fastest supercomputers in the world with a combined peak speed of 460 TFlops. To get an idea of the speed computing throughput 460 teraflops represents， the press release states that these two systems will have more than one-and-a-half times the combined processing power of all 500 machines on the recently announced TOP 500 List of Supercomputers.
① influentialadj. 有影响的；有权势的
② vacuumn. 真空[C]
③ previouslyadv. 事先；以前
④ continuationn. (间断后的)再开始；继续不断；延续
⑤ innovationn. 革新，改革，创新[U]
⑥ gleanv. 点滴搜集(消息、材料等)
计算机的历史与未来
很难确切地说现代计算机是什么时候发明的。从20世纪30年代到40年代，制造了许多类似计算机的机器。但是这些机器大部分没有今天我们所说的计算机的所有特征——机器是电子的，具有储存的程序，而且是通用的。
也许早期最具影响力的类似计算机的装置应该是电子数字积分计算机，或简称ENIAC。它是由宾夕凡尼亚大学的J. Presper Eckert和John Mauchly研制的。该工程于1943年开始，并于1946年完成。这台机器极其庞大，重达30吨，而且包含18，000多个真空管。
第一代计算机的特色是使用真空管为其主要电子器件。真空管体积大且发热严重，因此第一代计算机体积庞大，并且需要大量的空调设备保持冷却。此外，因为真空管运行不是很快，这些计算机运行速度相对较慢。
在第一代计算机期间，软件方面的其他的进展包括1957年FORTRAN语言的设计。这种语言成为第一种广泛使用的高级语言。同时，第一个简单的操作系统随着第一代计算机而出现。
在第二代计算机中，晶体管取代了真空管。虽然发明于1948年，但第一台全晶体管计算机直到1959年才成为现实。晶体管比真空管体积小、价格低，而且运行快而发热少。因此，随着第二代计算机的出现，计算机的体积和成本降低、速度提高，且它们对空调的需要减少。
许多先前不经销计算机的公司随着第二代计算机的出现进入计算机行业，其中今天仍然制造计算机的公司之一是控制数据公司(CDC)，他们以制造用于科学工作的高速计算机而著名。
作为第三代计算机标志的技术发展是在计算机中使用集成电路或简称IC。一个集成电路就是包含许多晶体管的一个硅片(芯片)。一个集成电路代替了计算机中的许多晶体管，导致了始于第二代的一些趋势的继续。这些趋势包括计算机体积减小、成本降低、速度提高和对空调的需要减少。
第四代计算机比其他三代更难以定义。这一代计算机的特征是一个芯片上包含越来越多的晶体管。首先，出现了一个芯片上具有数百和数千个晶体管的大规模集成电路(LSI)，接着出现了一个芯片上具有数万和数十万个晶体管的超大规模集成电路(VLSI)。这个趋势在今天仍在持续。
我们可能已经定义了我们最新一代计算机而且开始了计算机的无代时代。即使计算机制造商谈到 “第五”和 “第六”代计算机，这些说法更多是市场行为，而不是真实的反映。
无代计算机使科技革新接二连三地迅速出现，没有一种革新是，或将是足够重要，作为另一代计算机的特征。
从美国能源部发行的通告中，可以收集一些有关在不久的将来超级计算机设计中可能发生的事情的概念。它来自在马里兰州巴尔的摩市召开的2002年超级计算会议。该通告称能源部已给IBM拨款2.9亿美元建造世界上最快的两部超级计算机，其最高综合速度为每秒460兆兆次。为了理解每秒460兆兆次速度的含义，通告解释：这两个系统将会具有最近发布的500强超级计算机的总处理能力的1.5倍还多。