Input, output and memory devices; storage hierarchy

Key Points at a Glance

1. 1

   Input-process-output-storage is the working cycle: input devices capture data, the CPU processes it, memory supports current work, output devices present results, and storage preserves data for later use.

2. 2

   Device classification rule: classify by the main direction of data flow; keyboard, scanner and microphone are input devices, monitor, printer and speaker are output devices, and a touchscreen is both input and output.

3. 3

   RAM is volatile read-write main memory used for active programmes and data; ROM is non-volatile memory used for firmware or start-up instructions.

4. 4

   Storage hierarchy by usual access speed is registers, cache, RAM, SSD, HDD, optical disc and magnetic tape; speed generally decreases as capacity and low cost improve.

5. 5

   One byte = 8 bits and one nibble = 4 bits; one hexadecimal digit represents 4 bits, so two hexadecimal digits represent one byte.

6. 6

   Decimal to binary method: divide repeatedly by 2 and read remainders from bottom to top; for example, 45 decimal = 101101 binary.

7. 7

   Binary to decimal method: multiply each bit by its power-of-2 place value; for example, 110010 binary = 32 + 16 + 2 = 50 decimal.

8. 8

   A file system organizes stored files and folders through names, locations, permissions, size and extensions; saving a file and keeping a file open in memory are different actions.

9. 9

   Common error warning: an SSD is secondary storage, cache is faster than RAM, ROM is not the same as RAM, and storage capacity does not by itself measure processing speed.