Random Access

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Random Access : 

Random Access In this type of accessing method, the memory location can be reached by just specifying the address. An example of device that uses this type of Random Access method is RAM and ROM.

Memory capacity : 

Memory capacity The smallest storage unit inside the computer is the bit. The bit contains either 0 or 1 Inside computer, each character is represented by 8 bits (one Byte) The compute manufactures agree that each character has a specific sequence of bits. Example : (A) is represented by 01000001(1 byte).

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Example: of representing A, B, and C in memory:

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The capacity for memories can be measured by some units such as:

Memory types : 

Memory types There are two main types of memory: Primary Storage Secondary Storage

Primary Storage : 

Primary Storage Primary storages are units which used to store data and information temporary. It is a volatile memory. Primary storage devices are more expensive than secondary storage devices. Primary storage devices use random access method.

types of primary storage devices : 

types of primary storage devices There are many types of primary storage devices, the most famous types are: Random Access Memory (RAM) Read-only memory (ROM) Cache Memory Programmable ROM (PROM)

1. Random Access Memory (RAM) : 

1. Random Access Memory (RAM) It is a volatile memory, which means that the data will be lost when the power turn off. This type of memory used to save data temporarily (for short period of time). Computer processing speed depends on the size of RAM, more RAM means more processing speed. User has no direct access to this memory.

2. Read-only memory (ROM) : 

2. Read-only memory (ROM) It is nonvolatile memory, which means that the data will not be lost when the power turn off. It contains data that guide the computer when starting up and other instructions. ROM is read only memory which means that the CPU has no ability to make any change of this memory. User has no access to this memory. ROM capacity depends on ROM manufactures and the requirements.

Cache Memory : 

Cache Memory It is a type of memory which is used to store instructions that are used most often in the CPU. Cache memory is located between CPU and RAM. Cache memory is faster than RAM because the instructions travel shorter distance to the CPU. The advantage of cache memory is increasing the computer processing speed. The disadvantages of cache are that it is expensive and has small size.

4. Programmable ROM (PROM) : 

4. Programmable ROM (PROM) It is a type of ROM that can be programmed. It comes without instructions and the user program it according to his requirements. Once PROM programmed, it is not possible to make any changes or reprogram it. There are other types of ROM memories such as EPROM (can be erased and programmed again)

Secondary Storage : 

Secondary Storage Secondary storages are units which used to store data, information, systems software, and applications software permanently (nonvolatile). It can store huge amount of data. It is cheaper than primary storage.

types of storage devices : 

types of storage devices There are many types of storage devices, the most famous types are: Floppy Disks Hard Disks Compact Disk (CD) Digital Video Disk (DVD)

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