The following material is from the Computer History Museum Historical Computers

1944-Harvard Mark-1 Conceived by Harvard professor Howard Aiken, and designed and built by IBM, the Harvard Mark-1 was a room-sized, relay-based calculator. The machine had a fifty-foot long camshaft that synchronized the machine’s thousands of component parts. The Mark-1 was used to produce mathematical tables but was soon superseded by stored program computers.

1946- February, the public got its first glimpse of the ENIAC, a machine built by John Mauchly and J. Presper Eckert that improved by 1,000 times on the speed of its contemporaries. Start of project: 1943Completed: 1946Programmed:plug board and switches Speed:5,000 operations per second Input/output:cards, lights, switches, plugs Floor space:1,000 square feet Project leaders:John Mauchly and J. Presper Eckert.

Punch Cards The IBM card format, designed in 1928, had rectangular holes, 80 columns with 12 punch locations each, one character to each column. Card size was exactly by mm.IBM1928 The top two positions of a column were called zone punches, 12 (top) and 11. These often encoded plus and minus signs. The lower ten positions represented (from top to bottom) the digits 0 through 9. Originally only numeric information was coded, with 1 or 2 punches per column: digits (digit [0-9]) and signs (zone [12,11] ). Later, codes were introduced for upper-case letters and special characters. A column with 2 punches (zone [12,11,0] + digit [1-9]) was a letter; 3 punches (zone [12,11,0] + digit [2-4] + 8) was a special character.

IBM Keypunch Machine 026

In 1953, Jay Forrester invented “coincident current addressing”, which made core memory practical. In this scheme, the current needed to magnetize the core is split between two wires (one horizontal, the other vertical). Only the core at the intersection of two electrified wires will change magnetization. In order to read a single core, a third wire is threaded through all the cores of a plane. When a core is magnetized to a “0,” a pulse occurs on this sense wire only if that core had been a “1” and not if it was already a “0.” This is destructive readout, since if it was a “1” it now needs to be rewritten. Consequently, it takes two cycles to read core memory, one to read the contents and another to reset it to its original state Early computers were limited because there was no way to build reliable and high-speed memory memory. Magnetic core solved these problems and subsequently became the dominant form of computer memory for more than 20 years. Core memory uses a 3-dimensional array of tiny ferrite rings to store data or programs. Each ring stores a single bit and is magnetized in either a clockwise or counterclockwise direction, representing a “0” or a “1” respectively. The cores are magnetized by a current flowing in wires that are threaded through each core. The direction of the current determines the direction of the magnetization

1951-The UNIVAC I delivered to the U.S. Census Bureau was the first commercial computer to attract widespread public attention. Although manufactured by Remington Rand, the machine often was mistakenly referred to as the "IBM UNIVAC." Remington Rand eventually sold 46 machines at more than $1 million each.F.O.B. factory $750,000 plus $185,000 for a high speed printer. Speed:1,905 operations per second Input/output:magnetic tape, unityper, printer Memory size:1, digit words in delay lines Memory type:delay lines, magnetic tape Technology:serial vacuum tubes, delay lines, magnetic tape Floor space:943 cubic feet Cost:F.O.B. factory $750,000 plus $185,000 for a high speed printer Project leaders:J. Presper Eckert and John Mauchly

1961-IBM 1301 Disk Storage Unit is released. The IBM 1301 Disk Drive was announced on June 2nd, 1961 for use with IBM’s 7000-series of mainframe computers. Maximum capacity was 28 million characters and the disks rotated at 1,800 R.P.M. The 1301 leased for $2,100 per month or could be purchased for $115,500. The drive had one read/write arm for each disk as well as flying heads, both of which are still used in today’s disk drives.

IBM 1311 Disk Storage Drive is announced. Announced on October 11, 1962, the IBM 1311 was the first disk drive IBM made with a removable disk pack. Each pack weighed about ten pounds, held six disks, and had a capacity of 2 million characters. The disks would rotate at 1,500 RPM and were accessed by a hydraulic actuator with one head per disk. The 1311 offered some of the advantages of both tapes and disks.

ASCII — American Standard Code for Information Interchange — permitted machines from different manufacturers to exchange data. ASCII consists of 128 unique strings of ones and zeros. Each sequence represents a letter of the English alphabet, an Arabic numeral, an assortment of punctuation marks and symbols, or a function such as a carriage return.

Transistors and Transistor based circuit boards

IBM announced the System/360, a family of six mutually compatible computers and 40 peripherals that could work together. The initial investment of $5 billion was quickly returned as orders for the system climbed to 1,000 per month within two years. At the time IBM released the System/360, the company was making a transition from discrete transistors to integrated circuits, and its major source of revenue moved from punched-card equipment to electronic computer systems

Hewlett-Packard entered the general purpose computer business with its HP-2115 for computation, offering a computational power formerly found only in much larger computers. It supported a wide variety of languages, among them BASIC, ALGOL, and FORTRAN.

Magnetic Drums Developed in the 1950s, magnetic drums were the first mechanical “direct access” storage devices. Typically, drums were made of a nickel-cobalt substrate coated with powdered iron. Data was recorded by magnetizing small surface regions organized into long tracks of bits. Unlike tape, data could be accessed randomly without having to skip large sections of unwanted information. Prior to the development of magnetic core memory, drums were used as main memory for several low cost computers such as the IBM 650, LGP-30 and Bendix G-15.

Magnetic Tapes Magnetic tape has been used to store digital information since at least 1951 when Presper Eckert and John Mauchly used it in the UNIVAC I computer. Their tape was made of metal, but later tapes have been made mostly of plastic. Some users of punched cards were initially reluctant to use tape because they could no longer see their data. IBM’s invention of the “vacuum channel” tape drive and improved magnetic materials resulted in reliable large-capacity tapes, which even reluctant customers eventually adopted. Tape data formats vary widely, and bit density has increased dramatically. Tape has now been largely replaced by hard disks for secondary storage, but it is still used for backing up of data.

Magnetic Disks In the 1950s, engineers attempted to develop a device that would provide efficient secondary storage, but also, unlike tape drives, provide random access to data. IBM succeeded by inventing the magnetic disk at their San Jose laboratories in Developed as part of a larger system known as RAMAC, the first Model 350 disk drive contained inch diameter disks and stored a total of five megabytes. IBM later added removable disk platters to its drives as featured on the IBM These platters provided archival data storage. IBM also was the first to hermetically seal both platters and read/write heads in a single enclosure in its Model 3340 Winchester disk drive. Today, all disk drive manufacturers employ this design convention. A sampling of the wide variety of disk shapes and sizes can be seen here.

1972 – PDP 11/40 Minicomputer DEC developed the PDP-11 as a family of 16-bit minicomputers that could grow with customers as their computing needs increased. From the first PDP- 11/20 in 1970 through the PDP-11/94 in 1990, DEC produced a variety of compatible machines and sold over 500,000. Much like the 12-bit PDP-8 before it, DEC further integrated the PDP-11 family until in 1982 it had placed one of its largest models, the PDP-11/70, on two large- scale integrated circuits. Since the PDP-8 and PDP-11 systems were subject to export restrictions, Soviet bloc computer companies commonly cloned the systems and packaged them under different names. Memory Type:Core Speed:1.25 MHz + Memory Size:56K+ Cost:$20,000 + Memory Width:(16-bit)

The Commodore PET (Personal Electronic Transactor) — the first of several personal computers released in 1977 — came fully assembled and was straightforward to operate, with either 4 or 8 kilobytes of memory, two built-in cassette drives, and a membrane "chiclet" keyboard.

The Apple II became an instant success when released in 1977 with its printed circuit motherboard, switching power supply, keyboard, case assembly, manual, game paddles, A/C powercord, and cassette tape with the computer game "Breakout." When hooked up to a color television set, the Apple II produced brilliant color graphics.

1981- IBM Personal Computer Although IBM’s first personal computer arrived nearly ten years after others were available, the IBM Personal Computer (PC) instantly legitimized and expanded the market. Unlike most other contemporary IBM products, the PC incorporated both hardware (the Intel 8088 microprocessor) and software made by other companies. IBM published design details in their manuals that encouraged others to make copies or “clones” of the original machine, often with improved functionality. The IBM PC architecture quickly became an industry standard. Memory Type:SemiconductorSpeed:4.77 MHz Memory Size:16KCost:$1,565 Memory Width:(8-bit)

1982 -Commodore introduces the Commodore 64. The C64, as it was better known, sold for $595, came with 64KB of RAM and featured impressive graphics. Thousands of software titles were released over the lifespan of the C64. By the time the C64 was discontinued in 1993, it had sold more than 22 million units and is recognized by the 2006 Guinness Book of World Records as the greatest selling single computer model of all time.