Many home computers were superficially similar. Most had a keyboard integrated into the case; sometimes a cheap-to-manufacture chiclet keyboard in the early days, although full-travel keyboards quickly became universal due to overwhelming consumer preference. Most systems could use an RF modulator to display 20–40 column text output on a home television. Indeed, the use of a television set as a display almost defines the pre-PC home computer. Although dedicated composite or “green screen” computer displays were available for this market segment and offered sharper text display and sometimes increased graphics resolution, a monitor was often a later purchase only made after users had bought a floppy disk drive, printer, modem, and the other pieces of a full system. This “peripherals sold separately” approach is another defining characteristic of the home computer era. Many first time computer buyers brought a base C-64 system home and hooked it up to their TV only to find they needed to purchase a disk drive or Datassette before they could make use of it as anything but a game machine.
In the early part of the 1980s, home computers were mostly based on 8-bit microprocessor technology, typically the MOS Technology 6502 or the Zilog Z80. A notable exception was the TI-99 series, announced in 1979 with a 16-bit TMS9900 CPU.
Processor clock rates were typically 1–2 MHz for 6502 based CPU’s and 2–4 MHz for Z80 based systems (yielding roughly equal performance), but this aspect of performance was not emphasized by users or manufacturers, as dealing with the systems’ limited RAM capacity, graphics capabilities and storage options took priority. Clock speed was considered a technical detail of interest only to users needing accurate timing. To economize on component cost, often the same crystal used to produce color television compatible signals was also divided down and used for the processor clock. This meant processors rarely operated at their full rated speed, and had the side-effect that European and North American versions of the same home computer operated at slightly different speeds and different video resolution due to different television standards.
Many home computers initially used the then-ubiquitous compact audio cassettes as a storage mechanism. Most cassette implementations were notoriously slow and unreliable, but floppy disk drives as found on more costly business-oriented microcomputers were expensive and used disks eight inches wide at the beginning of the home computer era. Costs declined toward the end of the 1980s as sales of microcomputers increased and mass production of 5.25″ drive mechanisms enabled economy of scale. The 5.25″ floppy disk drives would remain the standard throughout the 8-bit era. Though external 3.5″ drives were made available for most systems toward the latter part of the decade, most software for 8-bit home computers remained sold on 5.25″ disks; 3.5″ drives were used for data storage. Standardization of disk formats was not common; sometimes even different models from the same manufacturer used different disk formats. Various copy protection schemes were developed for floppy disks but most were broken in short order, and many users would only tolerate them for games as wear and tear on disks was a significant issue in an entirely floppy-based system, and having a backup disk of vital application software was seen as important. Copy programs that advertised their ability to copy or even remove common protection schemes were a common category of utility software in this pre-DMCA era.
In contrast to modern computers, home computers most often had their OS stored in ROM chips. This made startup times very fast – no more than a few seconds – but made OS upgrades difficult or impossible without buying a new unit. Usually only the most severe bugs were fixed by issuing new ROMs to replace the old ones at the user’s cost. The user interface was usually only a BASIC interpreter coupled to a character-based screen or line editor, with applications performing all other OS duties themselves. As multitasking was not common on home computers until late in the ’80s, this lack of API support wasn’t much of a liability. Application programs usually accessed hardware directly to perform a specific task, often “switching out” the ROM based OS anyway to free the address space it occupied and maximize RAM capacity. In an enduring reflection of their early cassette-oriented nature, most home computers loaded their Disk Operating System (DOS) separately from the main OS. The DOS was only used to send commands to the floppy disk drive and needn’t be loaded to perform other computing functions. One notable exception was Commodore, whose disk drives actually contained a 6502 processor and Commodore DOS in ROM. Many home computers also had a cartridge interface which accepted ROM-based software. This was occasionally used for expansion or upgrades such as fast loaders, and application software on cartridge did exist, but the vast majority of cartridges were games.
From about 1985, the high end of the home computer market began to be dominated by “next generation” home computers using the 16-bit Motorola 68000 chip, which helped to enable the greatly increased abilities of the Amiga and Atari ST series. Clock rates on these systems were approximately 8 MHz with RAM capacities of 256 kB (for the base Amiga 1000 system) up to 1024 kB (1 megabyte, a milestone, first seen on the Atari 1040 ST). These systems had built-in 3.5″ floppy disks from the beginning but 5.25″ drives were made available to facilitate data exchange with the IBM PC compatibles. The Amiga and ST both had GUIs inspired by the Apple Macintosh, but at a list price of $2495 (over $5000 in 2007 dollars), the Macintosh itself was too expensive for most households.
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