The IBM Personal Computer, commonly known as the IBM PC, is the original version and progenitor of the IBM PC compatible hardware platform. It is IBM model number 5150, and was introduced on August 12, 1981. It was created by a team of engineers and designers under the direction of Don Estridge of the IBM Entry Systems Division in Boca Raton, Florida.
Alongside "microcomputer" and "home computer", the term "personal computer" was already in use before 1981. It was used as early as 1972 to characterize Xerox PARC's Alto. However, because of the success of the IBM Personal Computer, the term PC came to mean more specifically a microcomputer compatible with IBM's PC product.
The 5150 system unit had only five expansion slots, and one was taken up by either a monochrome or colour display adapter. Almost all systems sold had at least one floppy drive, which required another slot for the controller card. Each serial and parallel port took up a further slot. The 5150's 63W power supply was slightly underrated for running contemporary hard drives. IBM's official solution to these problems was the 5161 Expansion Chassis.
The "IBM 5161 Expansion Chassis" came with one 10 MB hard disk and allowed the installation of a second hard disk. The system unit had five expansion slots, and the expansion unit had eight; however, one of the system unit's slots and one of the expansion unit's slots had to be occupied by the Extender Card and Receiver Card, respectively, which were needed to connect the expansion unit to the system unit and make the expansion unit's other slots available, for a total of 11 slots. A working configuration required that some of the slots be occupied by display, disk, and I/O adapters, as none of these were built in to the 5150's motherboard; the only motherboard external connectors were the keyboard and cassette ports. The simple PC speaker sound hardware was also on-board.
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