Page 205 - Concise Encyclopedia of Robotics

Memory
entertaining. Anyone who has stayed in a hospital for more than a couple
of days knows how tedious it can become.A robot that can tell a few good
jokes can brighten any patient’s day.
See also PERSONAL ROBOT.
MEMORY
Memory refers to the storage of binary data in the form of high and low
levels (logic ones and zeros). There are several forms of memory.
The amount of memory capacity is a factor in determining how “smart”
a computer is. It is also helpful in choosing the right level of controller for a
robotic system. Memory is measured in bytes, kilobytes (kB), megabytes
(MB), gigabytes (GB), and terabytes (TB).
Random-access memory (RAM)
Random-access memory (RAM) chips store data in matrices called arrays.
The data can be addressed (selected) from anywhere in the matrix. Data
are easily changed and stored back in RAM, in whole or in part. A RAM
is sometimes called a read/write memory.
An example of RAM is a word-processing computer file.This definition
was written in semiconductor RAM, along with all the definitions of terms
starting with the letter M, before being stored on disk, processed, and
finally printed.
There are two kinds of RAM: dynamic RAM (DRAM) and static RAM
(SRAM). DRAM employs integrated-circuit (IC) transistors and capacitors;
data is stored as charges on the capacitors.The charge must be replenished
frequently, or it will be lost to discharge. Replenishing is done several
hundred times per second. SRAM uses a circuit called a flip-flop to store
the data. This gets rid of the need for constant replenishing of charge,
but the trade-off is that SRAM chips require more elements to store a
given amount of data.
Volatile versus nonvolatile RAM
With any RAM, the data are erased when the appliance is switched off,
unless some provision is made for memory backup. The most common
means of memory backup is the use of a cell or battery. Modern IC mem-
ories need so little current to store their data that a backup battery lasts as
long in the circuit as it would on the shelf.A new form of nonvolatile RAM,
known as flash memory, can store large amounts of data indefinitely even
with the power removed.
A memory that disappears when power is removed is called a volatile
memory. If memory is retained when power is removed, it is nonvolatile.

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