Consequently, any external modem can be attached to any computer that has an RS-232 port , which almost all personal computers have. There are also modems that come as an expansion board that you can insert into a vacant expansion slot . These are sometimes called onboard or internal modems . While the modem interfaces are standardized, a number of different protocols for formatting data to be transmitted over telephone lines exist. At high transmission speeds, however, the protocols are less standardized.
Many disk drives improve their performance through a technique called caching .
There are several interface standards for passing data between a hard disk and a computer . The most common are IDE and SCSI . Hard disk drives are sometimes called Winchester drives, Winchester being the name of one of the first popular hard disk drive technologies developed by IBM in 1973. Zip disks are slightly larger than conventional floppy disks , and about twice as thick. They can hold 100 MB of data.