Memory of a computer is where program and data are stored before and after the calculations. Memory can retain the binary information stored in memory cells for varying amounts of time depending upon the type of memory. Every computer comes with a certain amount of physical memory, usually referred to as the main memory or the RAM. We can think of the main memory as an array of boxes, each of which can hold a single byte of information.
The four major characteristics of memory are:
a) Volatile memory
b) Non-volatile memory
c) Dynamic memory and
d) Static memory
Volatile Memories- are the semiconductor memories that loose their stored information when power is removed. Volatile memory is most suitable for applications requiring temporary storage.
Non-volatile Memories- Non-volatile memory retains stored information even when power is removed. It is suited to applications requiring permanent memory storage.
Dynamic Memory- Dynamic memories are memory devices that require periodic refreshing of the stored information. Refresh is restoring binary data stored in a particular memory location. The internal circuitry of dynamic memories uses a very simple capacitive charge storage circuit.
Static Memory- Static memories are designed to stored binary information without the necessity of periodic refreshes. Static memory stored less information per unit area of semiconductor material than dynamic memory.
The two common types of semiconductor memories are:
1.Read Only Memory (ROM)
2.Random Access Memory (RAM)
1. Read Only Memory (ROM)
Read Only Memory is semiconductor memory that has binary information or data stored permanently within the memory cells. The stored data can only be read by the user. But no information can be written into a standard ROM by the user. The data stored is coded into ROM by the manufacturer. Data in ROM is very secure. Thus, standard ROMs are used in applications in the same information must be used repeatedly. Microprocessor software codes of information that is coded into ROMs.
There are three types of ROM:
a) Programmable ROM: this is basically a special type of ROM chip that can be written to, but only once. Once operations have been written into PROM chip, they can’t be altered. This is also referred to as ‘burning’ or coding the memory.
b) Erasable PROM: EPROM can be erased and reprogrammed. Erasable PROM needs to be exposed to the concentrated ultra-violet (UV) light for a certain amount of time. Doing this wipes the data out, allowing it to be rewritten new instructions.
c) Electrically EPROM: Electrically EPROM is electrically erased by applying a high voltage to the appropriate pins of IC memory. All memory cells are erased in parallel, and new information can be programmed randomly. This ROM can be rewritten though the use of a special software program. Some special type of EEPROM that can be erased and programmed in blocks instead of one byte at a time, are called flash memory. Many modern PCs have their BIOS (basic input output system) stored on a flash memory chip so that it can be easily updated necessary.
2. Random Access Memory (RAM)
The other major type of memory is Random Access Memory (RAM), RAM is used for temporary storage of data and program instruction allowing performance to be optimum. For the CPU to work with this data, they must be read into a working memory storage, which is made up of RAM chips. Random Access Memory is volatile memory, meaning all data is lost when power is turned off. Random Access Memory is called RAM because any of the locations on a chip can be randomly selected and used to directly store and retrieve data and instructions. And because of their read/write operation, RAM is also called read-write memory. These are three basic types of Ram.
a. Dynamic RAM (DRAM)
b. Static RAM (SRAM)
c. Synchronous Dynamic RAM (SDRAM)
a. Dynamic RAM (DRAM)
Dynamic RAM is the more common type. DRAM needs to be refreshed thousands of times per second. DRAM consists of micro capacitors that are capable of storing charge. The charge on the capacitor tends to leak off, so in order to retain stored data, each memory needs to be refreshed.
b. Static RAM (SRAM)
Static RAM needs to be refreshed less often, which makes it faster; but it is more expensive than DRAM. It uses number of ON/OFF switches or transistors to store the binary information. Since they retain information for longer of time, they are used as cache memory.
c. Synchronous Dynamic RAM (SDRAM)
The SDRAM is the newest RAM type. Synchronous Dynamic RAM’s speed is synchronous meaning that it is directly dependent on the clock speed of the entire system. Synchronous Dynamic RAM is designed mainly to operate with stability at higher bus speeds such as 100MHZ. it has an access time of only 8-12 ns. The advantage of this Ram is the increased speed. It uses a pipelined design to cope up with speed of CPU. So this kind of RAM has better performance as data can be read or accessed with much greater speed.
The capacity of memory devices is the total amount of information that the device can store. It is measured in bit or byte.
Unit --------------- Team --------------------- Capacity (Bits)
B ------------------- Bit --------------------------- 1
B -------------------Byte -------------------------- 8
Kb ----------------- Kilobits -----------------------20^10 =1024
KB ----------------- Kilobyte --------------------- 2^10*8=8192
Mb ---------------- Mega bits -------------------- 2^20=1048576
Gb ---------------- Gigabits ---------------------- 2^30=1073741824
Cache Memory:
Cache Memory is small memory that lies between the CPU and the working memory (RAM) and/or inside the CPU. Moving data between RAM and CPU’s internal resisters is a much slower process, so we need the fast cache memory. The cache memory helps to store the information temporarily. During the data processing, the CPU first looks for the information in the cache memory and goes to the main memory or RAM if the information is not found in the cache. When the information is brought from the main memory it is also copied to the cache memory so that if the same data is needed next time it can be fetched form the cache memory. There are two types of cache memory available, one is Level-1 (L1) cache which is CPU- resident and its capacity is generally 256 KB. Another type of cache is Level-2 (L2) cache which is motherboard resident. L2 may have 512 or 1024 KB capacity.
The four major characteristics of memory are:
a) Volatile memory
b) Non-volatile memory
c) Dynamic memory and
d) Static memory
Volatile Memories- are the semiconductor memories that loose their stored information when power is removed. Volatile memory is most suitable for applications requiring temporary storage.
Non-volatile Memories- Non-volatile memory retains stored information even when power is removed. It is suited to applications requiring permanent memory storage.
Dynamic Memory- Dynamic memories are memory devices that require periodic refreshing of the stored information. Refresh is restoring binary data stored in a particular memory location. The internal circuitry of dynamic memories uses a very simple capacitive charge storage circuit.
Static Memory- Static memories are designed to stored binary information without the necessity of periodic refreshes. Static memory stored less information per unit area of semiconductor material than dynamic memory.
The two common types of semiconductor memories are:
1.Read Only Memory (ROM)
2.Random Access Memory (RAM)
1. Read Only Memory (ROM)
Read Only Memory is semiconductor memory that has binary information or data stored permanently within the memory cells. The stored data can only be read by the user. But no information can be written into a standard ROM by the user. The data stored is coded into ROM by the manufacturer. Data in ROM is very secure. Thus, standard ROMs are used in applications in the same information must be used repeatedly. Microprocessor software codes of information that is coded into ROMs.
There are three types of ROM:
a) Programmable ROM: this is basically a special type of ROM chip that can be written to, but only once. Once operations have been written into PROM chip, they can’t be altered. This is also referred to as ‘burning’ or coding the memory.
b) Erasable PROM: EPROM can be erased and reprogrammed. Erasable PROM needs to be exposed to the concentrated ultra-violet (UV) light for a certain amount of time. Doing this wipes the data out, allowing it to be rewritten new instructions.
c) Electrically EPROM: Electrically EPROM is electrically erased by applying a high voltage to the appropriate pins of IC memory. All memory cells are erased in parallel, and new information can be programmed randomly. This ROM can be rewritten though the use of a special software program. Some special type of EEPROM that can be erased and programmed in blocks instead of one byte at a time, are called flash memory. Many modern PCs have their BIOS (basic input output system) stored on a flash memory chip so that it can be easily updated necessary.
2. Random Access Memory (RAM)
The other major type of memory is Random Access Memory (RAM), RAM is used for temporary storage of data and program instruction allowing performance to be optimum. For the CPU to work with this data, they must be read into a working memory storage, which is made up of RAM chips. Random Access Memory is volatile memory, meaning all data is lost when power is turned off. Random Access Memory is called RAM because any of the locations on a chip can be randomly selected and used to directly store and retrieve data and instructions. And because of their read/write operation, RAM is also called read-write memory. These are three basic types of Ram.
a. Dynamic RAM (DRAM)
b. Static RAM (SRAM)
c. Synchronous Dynamic RAM (SDRAM)
a. Dynamic RAM (DRAM)
Dynamic RAM is the more common type. DRAM needs to be refreshed thousands of times per second. DRAM consists of micro capacitors that are capable of storing charge. The charge on the capacitor tends to leak off, so in order to retain stored data, each memory needs to be refreshed.
b. Static RAM (SRAM)
Static RAM needs to be refreshed less often, which makes it faster; but it is more expensive than DRAM. It uses number of ON/OFF switches or transistors to store the binary information. Since they retain information for longer of time, they are used as cache memory.
c. Synchronous Dynamic RAM (SDRAM)
The SDRAM is the newest RAM type. Synchronous Dynamic RAM’s speed is synchronous meaning that it is directly dependent on the clock speed of the entire system. Synchronous Dynamic RAM is designed mainly to operate with stability at higher bus speeds such as 100MHZ. it has an access time of only 8-12 ns. The advantage of this Ram is the increased speed. It uses a pipelined design to cope up with speed of CPU. So this kind of RAM has better performance as data can be read or accessed with much greater speed.
The capacity of memory devices is the total amount of information that the device can store. It is measured in bit or byte.
Unit --------------- Team --------------------- Capacity (Bits)
B ------------------- Bit --------------------------- 1
B -------------------Byte -------------------------- 8
Kb ----------------- Kilobits -----------------------20^10 =1024
KB ----------------- Kilobyte --------------------- 2^10*8=8192
Mb ---------------- Mega bits -------------------- 2^20=1048576
Gb ---------------- Gigabits ---------------------- 2^30=1073741824
Cache Memory:
Cache Memory is small memory that lies between the CPU and the working memory (RAM) and/or inside the CPU. Moving data between RAM and CPU’s internal resisters is a much slower process, so we need the fast cache memory. The cache memory helps to store the information temporarily. During the data processing, the CPU first looks for the information in the cache memory and goes to the main memory or RAM if the information is not found in the cache. When the information is brought from the main memory it is also copied to the cache memory so that if the same data is needed next time it can be fetched form the cache memory. There are two types of cache memory available, one is Level-1 (L1) cache which is CPU- resident and its capacity is generally 256 KB. Another type of cache is Level-2 (L2) cache which is motherboard resident. L2 may have 512 or 1024 KB capacity.
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