A Brief History of Digital Hardware


When it began in 1957, DEC's engineers built logic modules, such as simple AND and OR gates, but by 1959, the engineers realized that these modules could become the basis of a computer. That is when the company built its first computer and called it the PDP-1. PDP is an acronym for programmable data processor; the word computer was still missing from DEC's terminology. In that era, fundamental computer architecture was still fluid, and DEC engineers were experimenting to find the optimum configuration. At that time the best combination of word size, register configuration, and instruction set had yet to be determined. Furthermore, the silicon technology was changing rapidly. The PDP-1, -4, -7, -9, and -15 were 18-bit machines; the PDP-5, -8, and -15 were 12-bit machines; and the PDP-6 and -10 were 36-bit machines. In many cases, these machines were being developed in parallel. The engineers did not achieve the best blend of features until the PDP-11, a 16-bit complex instruction set computer (CISC), which was released in 1970. DEC built more than 600,000 PDP-11s in various forms over the next 20 years. That machine is still manufactured and sold today, but not by Compaq/HP; it is licensed to Mentec.

By the mid-1970s, even though the PDP-11 was a tremendous success, DEC engineers recognized that its address space was too small, only 128K bytes, to keep up with software demands. In 1978 the VAX (Virtual Address eXtension to the PDP-11) was released. The VAX is a 32-bit CISC with more than 300 instructions. This machine was another hit for Olsen and DEC.

Once again, in 1993, the small computer was rocked by the AXP (not an acronym, just three letters) developed by DEC. This is a 64-bit RISC, an architecture deemed necessary because the industry had outgrown the VAX, just as it outgrew the PDP-11. The engineers believed the VAX had too little growth potential in CPU speed and address space. The AXP was later renamed the Alpha.

DEC was in decline, however. The introduction of the Alpha was far behind Sun's SPARC (a 32-bit RISC) designed in 1985 and HP's RISC work as well. In the late 1980s, the SPARC had effectively replaced DEC in the engineering workstation market. Even though Sun's 64-bit RISC was introduced about the same time as the Alpha, Sun's customer base remained loyal. DEC defined the "small" [2] computer industry (i.e., small compared with IBM's 360 mainframe series). DEC led that industry until the late 1980s.

[2]Digital engineers first coined the term minicomputer for the PDP-8 to describe their product line. The PDP-8 was the first computer to be priced at less than $10,000.




Getting Started with OpenVMS System Management
Getting Started with OpenVMS System Management (HP Technologies)
ISBN: 1555582818
EAN: 2147483647
Year: 2004
Pages: 130
Authors: David Miller

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