The Prime Memory is divided in to two main groups:
[1] Read/ Write Memory (R/WM) or Random Access Memory (RAM)
[2] Read Only Memory (ROM)
[1] Read/ Write Memory (R/WM) or Random Access Memory (RAM)
As the name suggest, the microprocessor can write into or read from this memory.
It is used primarily for information that is likely to be altered, such as writing programs or receiving data.
This Memory is Volatile, meaning that when the Power is turned off, all the contents are destroyed.
Two types of R/WM memories which are
[A] Static Memory (SRAM)
[B] Dynamic Memory (DRAM)
[A] Static Memory (SRAM)
This memory is made of Flip-flops, and it stores the bit as a voltage. Each memory cell requires six transistors; therefore the memory chip has low density but high speed.
This memory is more expansive and consumes more power than the dynamic memory described in next part. In high-speed Processors, SRAM known as cache memory is included on the processor chip.
In addition, high-speed cache memory is also included external to the processor to improve the performance of a system.
[B] Dynamic Memory (DRAM)
This memory is made of MOS transistor gates, and it stores the bit as a charge. The advantages of the dynamic memory are that it has high density and low power consumption and is cheaper than static memory.
The disadvantage is that the charge(bit information) leaks; therefore, stored information needs to be read and write again every few milliseconds. This is called Refreshing the memory, and it requires extra circuitry, adding to the cost of the system.
It is generally economical to use dynamic memory when the system memory size is at least 8K.
[2] Read Only Memory (ROM)
The ROM is a nonvolatile memory; it retains stored information even if the power is turned off.
This memory is used for programs and data that need not be altered. As the name suggest, the information can be read only, which means once a bit patten is stored , it is Permanent or at least Semi permanent.
The Permanent group is include two types of memory,
[A] Masked ROM
[B] Programmable ROM
[A] Masked ROM
In this ROM, a bit patten is permanenty recorded by the Masking and Metalization Process. Memory manufacture are generally equipped to do this process. It is an expensive and specialized process, but economical for large production quntities.
[B] Programmable ROM
The memory has nichrome or polysilicon wires arrenged in a matrix; these wires can be functionally viewed as diodes or fuses.
This memory can be programmed by the user with a special PROM programmer that selectively burns the fuses according to the bit patten to be stored.
The process is known as "Burning the PROM" and the information stored is Permanent.
[1] Read/ Write Memory (R/WM) or Random Access Memory (RAM)
[2] Read Only Memory (ROM)
[1] Read/ Write Memory (R/WM) or Random Access Memory (RAM)
As the name suggest, the microprocessor can write into or read from this memory.
It is used primarily for information that is likely to be altered, such as writing programs or receiving data.
This Memory is Volatile, meaning that when the Power is turned off, all the contents are destroyed.
Two types of R/WM memories which are
[A] Static Memory (SRAM)
[B] Dynamic Memory (DRAM)
[A] Static Memory (SRAM)
This memory is made of Flip-flops, and it stores the bit as a voltage. Each memory cell requires six transistors; therefore the memory chip has low density but high speed.
This memory is more expansive and consumes more power than the dynamic memory described in next part. In high-speed Processors, SRAM known as cache memory is included on the processor chip.
In addition, high-speed cache memory is also included external to the processor to improve the performance of a system.
[B] Dynamic Memory (DRAM)
This memory is made of MOS transistor gates, and it stores the bit as a charge. The advantages of the dynamic memory are that it has high density and low power consumption and is cheaper than static memory.
The disadvantage is that the charge(bit information) leaks; therefore, stored information needs to be read and write again every few milliseconds. This is called Refreshing the memory, and it requires extra circuitry, adding to the cost of the system.
It is generally economical to use dynamic memory when the system memory size is at least 8K.
[2] Read Only Memory (ROM)
The ROM is a nonvolatile memory; it retains stored information even if the power is turned off.
This memory is used for programs and data that need not be altered. As the name suggest, the information can be read only, which means once a bit patten is stored , it is Permanent or at least Semi permanent.
The Permanent group is include two types of memory,
[A] Masked ROM
[B] Programmable ROM
[A] Masked ROM
In this ROM, a bit patten is permanenty recorded by the Masking and Metalization Process. Memory manufacture are generally equipped to do this process. It is an expensive and specialized process, but economical for large production quntities.
[B] Programmable ROM
The memory has nichrome or polysilicon wires arrenged in a matrix; these wires can be functionally viewed as diodes or fuses.
This memory can be programmed by the user with a special PROM programmer that selectively burns the fuses according to the bit patten to be stored.
The process is known as "Burning the PROM" and the information stored is Permanent.
