Secondary Storage

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There are two kinds of memory:

• Volatile memory, which is storage, such as DRAM and cache, that retains data only if it is receiving power, and


• Non-volatile memory, which retains data even in the absence of a power source and is used to store programs between runs.

A secondary storage device is any non-volatile storage medium not directly accessible to the processor. It includes flash memory, floppy disks, hard disks, optical disks, magnetic tapes, punch cards, and paper tapes. Programs and data stored in secondary storage must first be loaded into main memory before the processor can use them.

The 2^X vs. 10^Y Bytes Ambiguity
The ambiguity happens when memory sizes are discussed. For example, originally terabyte (TB) means 2⁴⁰ bytes, although communications and storage systems developers started using the term to mean 10¹² bytes. This textbook resolves the ambiguity by adding a binary notation for all the common size terms. The last column shows how much larger the binary term is than its corresponding decimal term. These prefixes work for bits as well as bytes, so gigabit (Gb) is 10⁹ bits while gibibits (Gib) is 2³⁰ bits.

Decimal term	Abbreviation	Value	Binary term	Abbreviation	Value	% Larger
kilobyte	KB	10001	kibibyte	KiB	210	2%
megabyte	MB	10002	mebibyte	MiB	220	5%
gigabyte	GB	10003	gibibyte	GiB	230	7%
terabyte	TB	10004	tebibyte	TiB	240	10%
petabyte	PB	10005	pebibyte	PiB	250	13%
exabyte	EB	10006	exbibyte	EiB	260	15%
zettabyte	ZB	10007	zebibyte	ZiB	270	18%
yottabyte	YB	10008	yobibyte	YiB	280	21%
ronnabyte	RB	10009	robibyte	RiB	290	24%
queccabyte	QB	100010	quebibyte	QiB	2100	27%