The development of the computer - Mainframes, Midrange Computers, Personal Computers, Palmtops (Personal Digital Assistants).

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Contents

Title                                                                                Page Number

Mainframes                                                                                2

Midrange Computers                                                                        3

Personal Computers                                                                        4

Palmtops (Personal Digital Assistants)                                                 5

Glossary


Information Technology Coursework

Mainframes

Mainframes have been around for decades. They were the first systems to power businesses. They often took up extremely large spaces, were expensive to buy and required large amount of power and effort, using water-cooling or air conditioning systems to keep them at optimum temperature.

Mainframes are multi-user systems. They allow many users, from hundreds to thousands to work at the same time on different tasks.

Mainframes use the CISC instruction set. This stands for Complex Instruction Set Computer. It uses 18 different instruction formats, with system instructions being of variable length, 16bits, 32bits and 48bits. The instructions run directly between memory and the registers, and internally within the registers and the memory.

Originally the x86 was had 64kb of RAM which was expandable to 640kb. As there was no hard-drive, data was stored on tapes or 340kb floppy discs.

The CPU supported 16bit processing with the use of 16bit registers and 16bit data buses which were internal. Technology has progressed to the point where 64Gigabytes of Physical memory can be used today instead of the 1MB used previously.

The processors architecture has also changed. They have expanded in size from a 32bit to a 64bit which means the CPU can now carry out larger data instructions. The Registers have also been upgraded since the x68 was first made available to businesses. They have expanded up to sixteen 64bit general purpose registers and sixteen 64bit floating point registers within the mainframe itself. The General Purpose Registers hold data and addresses, and can also join together to allow the CPU to accept 128bit data.

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Addressing is performed in two stages within a mainframe. The first stage involves the instruction address that resides in the instruction pointer register and the data address that is calculated from an address stored in a register, indexed, or included as part of the instruction word.

The second stage translates the addressed calculated in stage one into an actual, physical memory address for which the data is to be accessed from.

Mainframes originally required a standard keyboard as input and its output was onto a low resolution, mono-coloured text. However at present the PC’s that are connected ...

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