Memory
Characteristics
Volatile memory
Volatile memory is a type of storage whose contents are erased when the system's power is turned off or interrupted. For example, RAM is volatile; meaning users will lose a document if they do not save their work to a non-volatile classification of memory, such as a hard drive, before shutting down the computer.Non-volatile
Non-volatile is a term used to describe any memory or storage that is saved regardless if the power to the computer is on or off. The best example of non-volatile memory and storage is a computer hard drive, flash memory, and ROM. If data is stored on a hard drive, it will remain on that drive regardless if the power is interrupted, which is why it is the best place to store your data and documents. This is also how your computer keeps the time and other system settings even when the power is off.Read-only memory
Read-only memory (ROM) is a type of storage medium that permanently stores data on personal computers (PCs) and other electronic devices. It contains the programming needed to start a PC, which is essential for boot-up; it performs major input/output tasks and holds programs or software instructions.Because ROM is read-only, it cannot be changed; it is permanent and non-volatile, meaning it also holds its memory even when power is removed. By contrast, random access memory (RAM) is volatile; it is lost when power is removed.
There are numerous ROM chips located on the motherboard and a few on expansion boards. The chips are essential for the basic input/output system (BIOS), boot up, reading and writing to peripheral devices, basic data management and the software for basic processes for certain utilities.
Read-write memory
Read-write memory is a type of electronic storage used by computers and other devices that can have information stored on it and, subsequently, can have that same information retrieved later. There are several physical forms of read-write memory, such as computer random access memory (RAM) chips, hard drives, and rewritable compact disks (CD-RWs) to name a few. The purpose of read-write memory can be to permanently store information for later use, such as is the case with a CD-RW, or it can be to provide an area of fast access to information that has been compiled or loaded, as is the case with RAM chips. There is a distinct functional difference between read-write memory, read-only memory (ROM) and write-only memory (WOM).
Primary Memory
1)
Primary storage, also known as main storage or memory, is the main area in a
computer in which data is stored for quick
access by the computer's processor. On today's smaller
computers, especially personal computers and workstations, the term random
access memory (RAM) - or just memory - is used instead of
primary or main storage, and the hard disk, diskette, CD, and DVD collectively describe secondary storage or auxiliary storage.
The
terms main storage and auxiliary storage originated in the days of the mainframe computer to distinguish
the more immediately accessible data storage from storage that required
input/output operations. An earlier term for main storage was core in the days
when the main data storage contained ferrite cores.
2)
Primary storage is sometimes used to mean storage for data that is in active
use in contrast to storage that is used for backup purposes. In this usage,
primary storage is mainly the secondary storage referred to in meaning 1. (It
should be noted that, although these two meanings conflict, the appropriate
meaning is usually apparent from the context.)
Related
glossary terms: hard disk, magnetoresistive head technology, yottabyte, serverless backup, byte, partition, InfiniBand, failover, RAMAC (random access method of
accounting and control), Fibre Channel
RAM
RAM,
or random access memory, stores information that is being processed and
offloads it at a very fast rate to the motherboard of the computer so it can be
sent to the northbridge, and then for use to the GUI (graphic user interface),
which allows the user to access the information with the mouse, keyboard,
monitor, etc.
Static RAM
Static
random-access memory (SRAM or static RAM) is a type of semiconductor memory that
uses bistable latching
circuitry to
store each bit. The term static differentiates it from dynamic RAM
(DRAM) which must be
periodically refreshed. SRAM exhibits data remanence,but it is still volatile in the conventional
sense that data is eventually lost when the memory is not powered.SRAM is more
expensive and less dense than DRAM and is therefore not used for high-capacity,
low-cost applications such as the main memory in personal computers.
Dynamic random access memory
Dynamic
random access memory (DRAM) is a type of random
access memory that stores each bit of
data in a separate capacitor within an integrated
circuit.
Since real capacitors leak charge, the information eventually fades unless the
capacitor charge is refreshed periodically.
Because of this refresh requirement, it is a dynamic memory as opposed
to SRAM and
other static memory.
SRAM
|
DRAM
|
It
is faster that DRAM.
|
It
is slower than SRAM.
|
It
is more expensive.
|
It
is less expensive.
|
It
does not need to be power- refreshed.
|
It
has to be refreshed after each read operation.
|
It
utilizes less power.
|
It
utilizes more power.
|
Processor Cache
The
processor, also known as the CPU (central processing unit), processes
information on your computer. In order to do this, it needs somewhere to store
the memory, which in this case is the "cache memory." The cache
memory transfers data at lightning fast speeds so it can be processed by the
cores in the processor. The cache memory holds a lot less space than RAM,
however. For example, a processor will usually have around 12 MB of cache
memory, whereas RAM may have up to 4 GB per stick. However, the cache memory
makes up for that in sheer speed. For instance, RAM will have a speed of 800
Mhz, while the cache memory can operate at 2.4 Ghz.
Processor Registers
The processor registers are the smallest of all primary storage devices. Typically, they hold around 32 to 64 bits, which is good enough for very simple processes such as math calculations. However, the processor registers are the fastest primary storage devices as well. They are primarily used by the processor to handle calculations used to operate the programs. The larger processes involving software and operating system files are handled by the cache memory.
Secondary memory
Secondary
memory (or secondary storage) is the slowest and cheapest form of memory.
It cannot be processed directly by the CPU.
It must first be copied into primary storage (also known as RAM
).
Secondary
memory devices include magnetic disks like hard drives and floppy disks ; optical disks such as CDs and CDROMs ; and magnetic tapes,
which were the first forms of secondary memory.
Auxiliary memory
Auxiliary memory, also known as auxiliary storage, secondary storage, secondary memory or external memory, is a non-volatile memory (does not lose the data when the device is powered down) that it is not directly accessible by the CPU, because is not accessed via the input/output channels (it is an external device). In RAM devices (as flash memory) data can be deleted or changed.
It is used to store a large amount of data at lesser cost per byte than primary memory, it is two orders of magnitude less expensive than primary storage.
Hard disk drive
Hard
disks are usually used as secondary storage in modern computers,. The time
taken to access a given byte of information stored on a hard disk is typically
a few thousandths of a second, or milliseconds and the time taken to access a
given byte of information stored in random access memory is measured in
billionths of a second, or nanoseconds. Hard disks are typically about a
million times slower than primary memory.
External Hard Disk
A hard drive that is outside of
the computer case in its own
enclosure. Most external hard drives support the IDE interface and are slightly
bigger than a hard drive itself. When purchasing an external hard drive you can
buy a full external hard drive system that consists of both the hard drive and
the enclosure, or you can purchase just the enclosure to hold your own hard
drive.
External
hard drives may contain a fan for cooling and are popular because they are
portable devices and can be stored securely under lock and key since they are
not inside the computer case. An external hard drive is connected to the
computer system with a single high-speed interface cable, usually with plug-and-play interfaces such
as USB
Optical storage devices
CD
and DVD drives used as optical storage devices. They have even longer access
times. With disk drives, once the disk read/write head reaches the proper
placement and the data of interest rotates under it, subsequent data on the
track are very fast to access. As a result, in order to hide the initial seek
time and rotational latency, data are transferred to and from disks in large
contiguous blocks.
Other examples of secondary storage technologies
Flash memory (e.g. USB flash drives or keys), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks and Iomega Zip drives.
Other examples of secondary storage technologies
Flash memory (e.g. USB flash drives or keys), floppy disks, magnetic tape, paper tape, punched cards, standalone RAM disks and Iomega Zip drives.
Pen drive
a pen drive is a portable Universal Serial Bus (USB) flash memory device for storing and transferring audio, video, and data files from a computer. As long as the desktop or laptop has a USB port, and the pen drive is compatible with the operating system, it should be easy to move the data from the hard drive to the device — and to another computer — in a matter of minutes. The drive gets its name from the fact that many have a retractable port connector like a ballpoint pen, and they are small enough to fit into a pocket. Other names include flash drive, jump drive, and thumb drive.
Transfer Speeds
The
actual transfer speed depends upon several factors, such as the computer's
speed at reading and writing to the device. Generally, a pen drive's advertised
speed is the reading speed because it is faster than the speed at which data
can be written to it. Manufacturers usually list the speed in megabytes per
second (MB/s). The age of the drive and how it's being used — such as for
writing and erasing small files — also affects the transfer speed.
Benefits
Equipped
with a large amount of memory, the pen drive is often considered to be an
improvement on both the older floppy drive disks and the more modern compact
disks. They can transfer data much more quickly than these older technologies.
Because they are solid state— there are no moving
parts — flash drives usually last longer and the data stored on them is safer.
Depending on the storage size, flash drives can hold anywhere from 128 MB to 32
GB or more; by comparison, a standard CD-ROM holds about 700 MB of data.
Memory card
A
memory card (sometimes called a flash memory card or a storage card) is a small
storage medium used to store data such as text, pictures, audio, and video, for
use on small, portable or remote computing devices.
Secure Digital Card
An
SD Card (Secure Digital Card) is an ultra small flash memory card designed to provide
high-capacity memory in a small size. SD cards are used in many small portable devices such as digital
video camcorders, digital cameras, handheld computers, audio players and mobile phones. In use since 1999, SD Memory Cards
are now available in capacities between 16 Megabytes and 1 Gigabyte. An SD card typically measures 32 x 24 x 2.1 mm and weighs
approximately 2grams.
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