Memory
Memory can be thought of as a set of pigeon holes or cells with
each one having a unique address. Each pigeon hole can store
8 bits of data. Older memory chips have 30 pins connecting the
memory chip to the computer. It is more typical to have 72 or
128 pins now. A computer contains two types of memory, Random
Access Memory (RAM) and Read Only Memory (ROM).
RAM
Random
Access Memory (RAM) is responsible for storing the instructions
and data that the computer is using at that present moment
in time.
RAM is described as volatile memory because the contents
of RAM chips can be lost when the computer is turned off
or when new data is being written to RAM while other data
is being processed.
RAM chips are produced on pieces of silicon in a manner
similar to that of microprocessors. Semiconductor RAM
memory can be divided into two major groups: Static RAM
and Dynamic RAM. |
|
| |
ROM
Read
Only Memory (ROM) is responsible for storing permanent
data and instructions. ROM chips have software (program
instructions) permanently etched into their circuitry.
For this reason, ROM is often referred to as firmware
because it's partly hardware and partly software.
Developments
in the storage capacity of ROM chips have enabled their
use in the storage of systems software. Previously, systems
software was stored on floppy disks. Other applications
of ROM can be found where a microprocessor is dedicated
to a particular task.
ROM
can be divided into several types: Mask programmed, PROM
(Programmable ROM), EPROM (Erasable Programmable ROM)
and EEPROM (Electrically Erasable Programmable ROM).
|
RAM
versus ROM
Both
RAM and ROM allow random access. To distinguish RAM from ROM,
you could call RAM read/write memory, meaning that you can both
retrieve (read) information from RAM, and record (write) information
to it. In contrast, instructions are frozen into the circuitry
of ROM. The feature that sets RAM apart from ROM is its changeability;
you can alter the contents of RAM at will.
The
other difference between RAM and ROM is how long their memories
last. RAM is short-term memory; it forgets everything it knows
as soon as you turn off your computer. ROM is long-term memory;
it remembers everything it has ever known as long as it lives.
It's the elephant of the memory kingdom. |
