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The History Of Computers During My Lifetime - The 1970's

by Jason Patterson
(jason@pattosoft.com.au)

The First General Purpose Microprocessor - The Intel 4004

By the time I was born (1972), Intel had already released the world's first generally available DRAM chip (the Intel 1103), and the world's first EPROM (the Intel 1702).

In 1971, responding to a request for a chip for a new calculator, and with incredible overkill, Intel built the world's first single chip general purpose microprocessor. Then it bought back the rights for $60,000. The 4-bit Intel 4004 ran at a clock speed of 108 kHz and contained 2300 transistors. It processed data in 4 bits, but its instructions were 8 bits long. The 4004 addressed up to 1 Kb of program memory and up to 4 Kb of data memory (as separate entities). It had sixteen 4-bit (or eight 8-bit) general purpose registers, and an instruction set containing 46 instructions.

UNIX and the C Programming Language

Meanwhile, at the other end of the industry, two talented programmers at AT&T Bell Laboratories (Brian Kernighan and Dennis Ritchie) invented the C programming language. C was far from being the first high level language, but its pointer arithmetic and low-level approach made it the first language which could completely replace assembly language programming, even for most of the internals of an operating system. C was the first systems programming language - no longer did an operating system need to be tied to a particular piece of hardware.

Simultaneously, other programmers at Bell Labs were busy building MULTICS - the ultimate operating system. In a rebellion against the size and complexity of MULTICS, Ken Thompson and Dennis Ritchie began building the UNIX operating system. Thanks to the C language, less than two man years were spent on the main system software. Several of the key features of UNIX - multitasking (which they called time-sharing), virtual memory, multi-user design and security - did not reach the personal computer market for another ten years, and didn't reach the mainstream IBM PC for almost twenty.

UNIX began life in 1970 on Digital's PDP-7, but it soon migrated to the larger PDP-11. By the time UNIX began to become popular (1974), a well configured PDP-11 had 768 Kb of core memory, two 200 Mb moving head disks (hard disks), a reel to reel tape drive for backup purposes, a dot-matrix line printer and a bunch of [dumb] terminals. This was a high end machine, and even a minimally configured PDP-11 cost about $40,000. Despite the cost, 600 such installations had been put into service by the end of 1974, mostly at universities.

The C language went on to become the dominant language used for both systems and application development in the 1980's. UNIX and the C language were intimately tied from the very beginning - the standard C library was essentially the original UNIX operating system API.

The Winchester Hard Disk Drive

In 1973, IBM developed what is considered to be the first true sealed hard disk drive. The drive was called the "Winchester" after the rifle of the same name. It used two 30 Mb platters. Over the following decade, sealed hard disks (often called Winchester disks) took their place as the primary data storage medium, initially in mainframes, then in minicomputers, and finally in personal computers starting with the IBM PC/XT in 1983. By the late 1980's hard disk capacity had improved by almost a thousand fold, with single hard disks able to store Gigabytes of data.

CP/M

Developed by Gary Kildall in 1974, CP/M stood for Control Program for Microcomputers. It was the first operating system to run on machines from different vendors. It also became the preferred operating system for software development on small systems. In the mid 1970's, CP/M looked like it would rule forever, but unfortunately the early personal computers chose not to use CP/M, electing instead to provide a BASIC interpreter as their primary "operating system".

The First Personal Computer - MITS Altair

Although the Altair wasn't actually the first personal computer, it was the first to grab attention. MITS sold 2000 of them in 1975 - more than any computer before it. Costing only $439, the Altair was a kit which you had to build yourself. It was based on Intel's 8-bit 8080 processor and included 256 bytes of memory (expandable to a few Kb), a set of toggle switches and an LED panel. If you wanted a keyboard, screen or storage device you had to buy expansion cards! For 4 and 8 Kb Altairs, MITS offered a BASIC interpreter. This interpreter was the first product developed by Bill Gates' and Paul Allen's new company, Microsoft.

Vector Supercomputers Arrive - The Cray-1

In 1976, Seymour Cray founded Cray Research and introduced the Cray-1, the fastest computer in the world at that time. The Cray-1 had the historically unique distinction of being simultaneously the fastest in the world, the most expensive, and the computer with the best price/performance.

The Cray-1 wasn't the first vector computer, but it was the first to have fast normal (scalar) performance as well as fast vector performance. Its efficient, pipelined design meant that the Cray-1 did everything fast. This was probably the most significant reason for its success - some customers bought it even though their problems were not vectorizable, purely for its fast general performance. Whatever the reason, the Cray-1 was the first successful vector supercomputer, and created a whole new market for high end vector machines and vectorizing compilers.

The Apple II

Steve Jobs and Steve Wozniak's Apple II was really the beginning of the personal computer boom. It debuted at the first West Coast Computer Faire in San Francisco in 1977. With a built-in keyboard, graphics display, and BASIC built into ROM, the Apple II was actually useful.

The Apple II was based on a MOS 6502 processor, had color graphics (a huge innovation), and used an audio cassette drive for storage. In its original configuration with just 4 Kb of RAM it cost $1298. A year later this was increased to 48 Kb of RAM with the introduction of the Apple II+. The cassette drive didn't work very well so in the end most Apple II owners bought the floppy disk drive when it was released in 1978.

MOS Technology's 6502 processor was chosen for the first Apple computers not because it was powerful, but because it was cheap. Introduced in 1975 at under $100 (compared with $375 for the similar Motorola 6800), the 6502 was a real bargain. The 6502 only had three 8-bit registers (accumulator, X and Y) plus an 8-bit stack pointer, but this made sense because at that time RAM was actually faster than processors, so it was better to optimize for RAM access rather than increase the number of registers on the chip. The instruction set contained 56 instructions which used 9 addressing modes. For a whole generation of programmers (myself included), 6502 assembly language was the second programming language they learned (BASIC was the first). Fifteen years later, the 6502 was still being used (in the Nintendo Entertainment System).

The Commodore PET

The PET was the beginning of a line of low cost Commodore computers which brought computing to the masses. Like the Apple II, the PET ran on the MOS 6502, but the PET cost only $795, which made it almost half the price of the Apple II. It included 4 Kb of RAM, monochrome graphics, and used an audio cassette drive for data storage. It also included a version of BASIC in ROM. The keyboard, cassette drive and small monochrome display all fit within the same trapezoidal one piece unit.

The Radio Shack TRS-80

Still in 1977, the TRS-80 (lovingly called the Trash-80) was the third of the first three consumer ready personal computers. The base unit was essentially a thick keyboard with 4 Kb of RAM and 4 Kb of ROM (which included BASIC). An optional expansion box enabled memory expansion. Software was distributed on audio cassettes played in from Radio Shack cassette recorders. Although it had some following, the TRS-80 was soundly defeated in the marketplace by the Apple II, and later by the Commodore 64.

Digital's VAX - The Minicomputer Revolution

Although UNIX started life in 1970 on Digital's PDP-11, Digital's VAX (introduced in 1977) became the dominant processor used to power the UNIX and VMS minicomputers which started the demise of the mainframe. VAX stood for Virtual Address eXtension to the PDP-11, and was a large and complex 32-bit CISC architecture. Processors which implemented the VAX architecture went through many revisions during its 20 year lifetime, and used a wide range of single and multi chip technologies. VAX processors scaled up to huge departmental super-minicomputers, and down to small desktop workstations. Despite this, the VAX architecture remained relatively stable throughout its lifetime, a testimony to its design.

Many people consider the VAX to be the ultimate CISC architecture - it had a huge number of instructions (over 300), including instructions for string manipulation, polynomial evaluation, and BCD. Most instructions could specify their arguments using any of the 13 addressing modes, allowing for memory-to-memory-to-memory operations! However, the complex instructions were not always the fastest way of doing things. For example, the INDEX instruction was 45% to 60% faster when by replaced by simpler VAX instructions. This was one inspiration for the RISC philosophy. Writing a compiler which did good instruction selection for the VAX was non-trivial.

The VAX-11/780 was introduced in 1977 at an entry price of about $200,000. The 11/780 had the distinction of being labeled as the speed benchmark for 1 MIPS (Million Instructions Per Second), even though its actual execution speed was only about 0.5 MIPS. Some people justified this by saying that 500,000 VAX instructions were equivalent to a million instructions for most other architectures (although I don't think it was quite that bad). Actually, the 1 MIPS label came from the fact that the VAX-11/780 was about the same speed as the IBM 370/158, which IBM marketed as a 1 MIPS machine. The VAX-11/780 became far more popular than the 370/158, so it ended up being the base machine for the relative MIPS measure and later the SPEC89 and SPEC92 benchmark suites.

VisiCalc

VisiCalc (released in 1979 running on an Apple II) was what really made people look at personal computers as business tools, not just toys. It was a very simple spreadsheet, but it did useful things and made life easier. VisiCalc was a godsend for Wall Street users. If the Apple II was the father of all personal computers, VisiCalc was the father of all personal productivity software.

      

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