The Hewlett Packard HP 9830 was one of the first desktop computers in the early 1970s to use automatically controlled cassette tapes for storage. It could save and find files by number, using a clear leader to detect the end of tape. These would be replaced by specialized cartridges such as the 3M DC-series. Many of the earliest microcomputers implemented the Kansas City standard for digital data storage. Most home computers of the late 1970s and early 1980s could use cassettes for data storage as a cheaper alternative to floppy disks, though users often had to manually stop and start a cassette recorder. Even the first version of the IBM PC of 1981 had a cassette port and a command in its ROM BASIC programming language to use it. However, this was seldom used, as even then floppy drives had become commonplace in high-end machines.
The typical encoding method for computer data was simple FSK which resulted in typical data rates of 500 to 2000 bit/s, although some games used special faster loading routines, up to around 4000-bit/s. A rate of 2000-bit/s equates to a capacity of around 660 kilobytes per side of a 90-minute tape.
Among home computers that primarily used data cassettes for storage in the late 1970s wereCommodore PET (early models of which had a cassette drive built-in), TRS-80 and Apple II, until the introduction of floppy disk drives and hard drives in the early 1980s made cassettes virtually obsolete for day-to-day use in the US. However, they remained in use on some portable systems such as the TRS-80 Model 100 line until the early 1990s. Due to the high price of disks, cassettes also remained the primary data storage medium for 8-bit computers, such as the Commodore 64,ZX Spectrum and Amstrad CPC 464, in many countries (for example, the UK, where 8-bit software was mostly sold on cassette until that market disappeared altogether in the early 1990s.)
In some countries, including the United Kingdom, Poland, Hungary and the Netherlands, audio cassette data storage was so popular that some radio stations would broadcast computer programs that listeners could record onto cassette and then load into their computer. SeeBASICODE.
The use of better modulation techniques like QPSK or those used in modern modems, combined with the improved bandwidth and signal to noise ratio of newer cassette tapes, allowed much greater capacities (up to 60 MB) and speeds (10–17 kB/s for data rate) on each cassette. These were typically used as hard disk backup for PCs in the late 1980s. They also found use during the 1980s in data loggers for scientific and industrial equipment.