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Memory
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Memory
The two main types of memory are random access memory (RAM) and read only memory
(ROM). Two types of RAM are static RAM (SRAM) and dynamic RAM (DRAM). There are
several types of ROM, including mask-programmed ROM, PROM, EPROM and EEROM.
Decoders are used to route signals to or from a specified location in memory. A real time clock
relieves the CPU of timekeeping duties.
There are two main types of memory:
Random access
memory
•
Random access memory − used for temporary storage. Data may
be written into it at any time, and later read from it The data is lost
when the power supply is switched off. Used for the storage of
data and for programs copied from more permanent data stores
such as magnetic disks.
•
Read only memory − used for permanent storage. In most types,
the data once written into it can not be changed. Used for storing
programs and data tables.
This occupies most of the available address space in a typical microcomputer. A PC when purchased may be equipped with 32 Mb of
RAM, with room for expansion to 64 Mb or more. The RAM is used
for the temporary storage of programs and data. There is usually less
need for RAM in a microcontroller system, as their programs are
permanent and are stored in ROM instead (see below). The RAM is