Input/Output and Memory Devices
Input/Output and Memory Devices
This domain checks input and output hardware, memory hierarchy, volatility and storage units. Input devices convert human-readable data into machine form: keyboard, mouse, scanner, joystick, microphone, barcode reader, OMR, OCR, MICR and biometric sensors. Output devices present results: monitors, printers, plotters and speakers. Impact printers strike the paper; non-impact printers do not.
Memory rules
Primary memory is directly accessed by the CPU: registers, cache, RAM and ROM. RAM is volatile and read/write; SRAM uses flip-flops and needs no refresh, DRAM uses capacitors and needs refresh. ROM is non-volatile: PROM is written once, EPROM erased by UV light, EEPROM electrically. Secondary storage is non-volatile and cheaper but slower: hard disk, SSD, optical disc, pen drive. Units: 8 bits = 1 byte; KB, MB, GB, TB. Access time increases as cost per bit falls down the hierarchy.
Worked example
Firmware such as a BIOS is best stored in EEPROM: it must survive power-off yet be updatable. A running program and its variables need RAM because the CPU can read and write it quickly. A student project backup belongs on secondary storage such as a hard disk or pen drive. Putting the BIOS in RAM would lose it at shutdown.
Traps
A pen drive is secondary, not primary. SRAM is faster than DRAM but costlier. ROM is not normally read/write for mask ROM. Printers are output; scanners input. Cache is smaller than main memory, not larger.