Why Did Early Computers Use a ROM OS?

ROM vs. RAM

Today’s computers boot their entire OS from disk. But back at the beginning, computers had their OS in ROM.

One big benefit of a ROM OS was that the computer would boot almost instantly.

For example, the Commodore 64, like most 8-bits, had its OS and BASIC in ROM. It also had its DOS in the ROM of the disk drive, which was somewhat unusual. But his all meant that it could boot in just a couple seconds and be ready to use.

An Atari 8-bit also had its OS (16K) and BASIC (8K) in ROM, but its DOS was loaded from disk so booting took 10+ seconds (and used up about 6K of RAM).

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