Memory

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Home * Hardware * Memory

RNA, biological data storage [1]

Memory is the ability to store, retain, and recall information and experiences as researched in cognitive science. Computer memory refers to physical devices used to store data and sequences of instructions (programs) on a temporary or permanent basis, typically distinguished as fast random-access memory and relatively slow data storage.

Flip-Flop

A flip-flop or latch is a one bit memory. For instance a simple relay (K1) with its contact parallel to the On-push-button S2, "remembers" whether last action was pushing S1 (reset) or S2 (set) [2] .

Selbsthaltung.gif

A RS flip-flop is a pair of cross-coupled NAND or NOR-gates, where the outputs are feed back to the inputs. A D flip-flop, the most common flip-flop, stores the input D with the rising edge (0-1 transition) of a clock.

RS flip-flop D flip-flop Discrete
RS flipflop.svg
D-Type Flip-flop.svg
Flipflop6as.jpg
R-S mk2.gif
Edge triggered D flip flop.svg
from two NOR (red == 1) [3] from six NAND [4] PDP-6 flip-flop [5] [6]

N-Bit Latches

N-Bit latches are arrays of one-bit latches or flip-flops typically as wide as a connected parallel data-bus. They may be used as a registers or scratchpad RAM inside a central processing unit.

RAM

Random access memory is a fast form of computer memory and refers to the idea that any piece of data can be stored and retrieved in a constant time, regardless of its physical location and whether or not it is related to the previous piece of data.

Static RAM

Static RAM (SRAM) is an array of latches, where each latch has a unique address, which connects the addressed latch to its data-bus, often used as CPU cache.

Dynamic RAM

Dynamic random access memory (DRAM) is a type of random access memory that stores each bit of data in a separate capacitor within an electronic circuit. Since capacitors leak charge, the information eventually fades unless the capacitor charge is refreshed periodically, which is the reason to call that memory dynamic. Since DRAM takes only one transistor and capacitor per bit, it is therefor used as cheap main memory part of recent computer data storage, despite its worse latency compared to SRAM.

Synchronous dynamic random access memory (SDRAM)
DDR SDRAM with Double data rate
Square array of mosfet cells read.png

DRAM write at a 4 by 4 array [7]

ROM

Read-only memory (ROM) is a class of storage programmed once and mainly used to distribute firmware. EPROMs have a small quartz window which admits UV light for erasure [8] . ROM or EPROM were often embedded inside a microcontroller in conjunction with some RAM. They were often used in dedicated chess computers.

EPROMs National Semiconductor.jpg

National Semiconductor EPROMs 2764 and 2716 [9]

Since each data-bit stored in a ROM is a boolean function of its inputs or address, a ROM is also used to implement combinatorial logic.

Auxiliary Storage

Historical Data Storage

Memory Hierarchy

Memory Management

Memory Model

Shared Memory

Shared Memory:

False sharing from Wikipedia

Cache

Cache:

MSI protocol from Wikipedia
MESI protocol from Wikipedia
MOESI protocol from Wikipedia
assembly - The prefetch instruction - Stack Overflow
Data Prefetch Support - GNU Project - Free Software Foundation (FSF)
Software prefetching considered harmful by Linus Torvalds, LWN.net, May 19, 2011

Segmentation

Allocation

Manual memory management
Memory leak
Garbage collection

Memory Footprint

Multiprocessing

Memory versus Search

See also

Publications

Computer Memory

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Memory part 1
Memory part 2: CPU caches
Memory part 3: Virtual Memory
Memory part 4: NUMA support
Memory part 5: What programmers can do

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Cognition

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  • Adriaan de Groot (1966). Perception and Memory versus Thought: Some Old Ideas and Recent Findings. Problem Solving: Research, Method, and Theory (ed. B. Kleinmuntz), pp. 19-50. John Wiley, New York.

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Forum Posts

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External Links

Computer Memory

Gustavo Duarte's Blog

from Best Of by Gustavo Duarte:

Cognition

Neuroscience

Misc

References