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33

Internal power supplies, while not universal, were not unusual at the time. The major considerations were cost, ease of design, and safety (that is, passing safety regulations that already existed in most first-world nations), with thermal considerations factoring in somewhere further down the list. The latter tended to point towards implementing a switch-...


11

Aside from Cromatix great answer, the thing to consider was difference in power. Typical home microcomputers (like ZX Spectrum or Commodore 64 etc) used power supplies with about 10-30 watts, while IBM PC XT has chunky 130W power supply (which increased to 192W SMPS in IBM AT). That much power requires much more space, and would be quite unwieldy as separate ...


6

The IBM PC wasn't a "home computer" -- it was intended to be a business computer, and needed to suit the needs of a business owner. Having the PS in the case eliminated extra connections (for the user) and made everything fit neatly on a desk. (And it should be pointed out that the PC was not IBM's first "personal computer". The IBM ...


5

The earliest personal computers of the 1970's, including the Altair 8800, had built in power supplies. The power supplies were often oversized to allow expansion boards to be added to the system. As the computers became smaller and more limited in expansion options (dare I say toy-like?) it became possible to power them with an external supply. It was ...


3

Another issue, outside the heat and multiple voltages issue, is the safety issue of low-voltage DC cabling. Home computers didn't draw much power, so a 5 – 12 V wall wart on a fairly short, thin two-conductor cable was considered safe enough. For example, the ZX Spectrum used a 9 V 0.7 – 1.4 A supply feeding a simple 7805 regulator, consuming ~650 mA at 5 V (...


3

Good points in earlier answers, but one is overlooked. The Ibm PC needs a set of different voltages, like +5V for the main board, +12V for disk drives, -5V for the RS-232 serial interface, -12V in case you have a special board that needs it. It would be quite impractical to have an external power supply connected with a cable to the PC with that many ...


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