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What is Computer Memory?
Computer memory is just like the human brain. It is used to store data/information and instructions. It is a data storage unit or a data storage device where data is to be processed and instructions required for processing are stored. It can store both the input and output can be stored here.
Characteristics of Computer Memory:-
*It is faster computer memory as compared to secondary memory. *It is semiconductor memories. *It is usually a volatile memory, and main memory of the computer. *A computer system cannot run without primary memory.
How Does Computer Memory Work?
When you open a program, it is loaded from secondary memory into primary memory. Because there are various types of memory and storage, an example would be moving a program from a solid-state drive (SSD) to RAM. Because primary storage is accessed more quickly, the opened software can connect with the computer’s processor more quickly. The primary memory is readily accessible from temporary memory slots or other storage sites. Memory is volatile, which means that data is only kept temporarily in memory. Data saved in volatile memory is automatically destroyed when a computing device is turned off. When you save a file, it is sent to secondary memory for storage. There are various kinds of memory accessible. It’s operation will depend upon the type of primary memory used. but normally, semiconductor-based memory is more related with memory. Semiconductor memory made up of IC (integrated circuits) with silicon-based metal- oxide-semiconductor (MOS) transistors.
Types of Computer Memory:-
In general, computer memory is of three types: 1.Primary memory 2.Secondary memory 3.Cache memory Now we discuss each type of memory one by one in detail:
1. Primary Memory:- It is also known as the main memory of the computer system. It is
used to store data and programs or instructions during computer operations. It uses semiconductor technology and hence is commonly called semiconductor memory. Primary memory is of two types: RAM (Random Access Memory): It is a volatile memory. Volatile memory stores information based on the power supply. If the power supply fails/ interrupted/stopped, all the data and information on this memory will be lost. RAM is used for booting up or start the computer. It temporarily stores programs/data which has to be executed by the processor. RAM is of two types: *S RAM (Static RAM): S RAM uses transistors and the circuits of this memory are capable of retaining their state as long as the power is applied. This memory consists of the number of flip flops with each flip flop storing 1 bit. It has less access time and hence, it is faster. Characteristics of Static RAM Static RAM is much faster than DRAM. Static RAM has greater storage than DRAM. Static RAM takes less power to perform. Advantages of Static RAM Static RAM has low power consumption. Static RAM has faster access speeds than DRAM. Static RAM helps in creating a speed-sensitive cache. Disadvantages of Static RAM Static RAM has less memory capacity. Static RAM has high costs of manufacturing than DRAM. Static Ram comprises of more complex design. *D RAM (Dynamic RAM): D RAM uses capacitors and transistors and stores the data as a charge on the capacitors. They contain thousands of memory cells. It needs refreshing of charge on capacitor after a few milliseconds. This memory is slower than S RAM. Characteristics of Dynamic RAM Dynamic RAM is slower in comparison to SRAM. Dynamic RAM is less costly than SRAM. Dynamic RAM has high power consumption.
SRAM DRAM
SRAMs are low-density devices. DRAMs are high-density devices. In this bits are stored in voltage form. In this bits are stored in the form of electric energy. These are used in cache memories. These are used in main memories. Consumes less power and generates less heat. Uses more power and generates more heat. SRAMs has lower latency DRAM has more latency than SRAM SRAMs are more resistant to radiation than DRAM DRAMs are less resistant to radiation than SRAMs SRAM has higher data transfer rate DRAM has lower data transfer rate SRAM is used in high-speed cache memory DRAM is used in lower-speed main memory SRAM is used in high performance applications DRAM is used in general purpose applications ROM (Read Only Memory): It is a non-volatile memory. Non-volatile memory stores information even when there is a power supply failed/ interrupted/stopped. ROM is used to store information that is used to operate the system. As its name refers to read-only memory, we can only read the programs and data that is stored on it. It contains some electronic fuses
that can be programmed for a piece of specific information. The information stored in the ROM in binary format. It is also known as permanent memory. ROM is of four types: Types of ROM: 1) Masked Read Only Memory (MROM): It is the oldest type of read only memory (ROM). It has become obsolete so it is not used anywhere in today's world. It is a hardware memory device in which programs and instructions are stored at the time of manufacturing by the manufacturer. So it is programmed during the manufacturing process and can't be modified, reprogrammed, or erased later. The MROM chips are made of integrated circuits. Chips send a current through a particular input- output pathway determined by the location of fuses among the rows and columns on the chip. The current has to pass along a fuse-enabled path, so it can return only via the output the manufacturer chooses. This is the reason the rewriting and any other modification is not impossible in this memory.
EPROM is a type of ROM that can be reprogramed and erased many times. The method to erase the data is very different; it comes with a quartz window through which a specific frequency of ultraviolet light is passed for around 40 minutes to erase the data. So, it retains its content until it is exposed to the ultraviolet light. You need a special device called a PROM programmer or PROM burner to reprogram the EPROM. Uses: It is used in some micro-controllers to store program, e.g., some versions of Intel 8048 and the Freescale 68HC11. 4) Electrically Erasable and Programmable Read Only Memory (EEPROM): ROM is a type of read only memory that can be erased and reprogrammed repeatedly, up to 10000 times. It is also known as Flash EEPROM as it is similar to flash memory. It is erased and
reprogrammed electrically without using ultraviolet light. Access time is between 45 and 200 nanoseconds. The data in this memory is written or erased one byte at a time; byte per byte, whereas, in flash memory data is written and erased in blocks. So, it is faster than EEPROM. It is used for storing a small amount of data in computer and electronic systems and devices such as circuit boards. Uses: The BIOS of a computer is stored in this memory. 5) FLASH ROM: It is an advanced version of EEPROM. It stores information in an arrangement or array of memory cells made from floating-gate transistors. The advantage of using this memory is that you can delete or write blocks of data around 512 bytes at a particular time. Whereas, in EEPROM, you can delete or write only 1 byte of data at a time. So, this memory is faster than EEPROM. It can be reprogrammed without removing it from the computer. Its access time is very high, around 45 to 90 nanoseconds. It is also highly durable as it can bear high temperature and intense pressure.
Assignment: - Difference between RAM and ROM
Difference
Random Access Memory
(RAM) Read Only Memory (ROM)
Cost RAM is more costlier than ROM. ROM is cheaper than RAM. Chip Size A RAM chip can store only a few gigabytes (GB) of data. A ROM chip can store multiple megabytes (MB) of data. Function Used for the temporary storage of data currently being processed by the CPU. Used to store firmware, BIOS, and other data that needs to be retained.
Secondary Memory
We have read so far, that primary memory is volatile and has limited capacity. So, it is
important to have another form of memory that has a larger storage capacity and
from which data and programs are not lost when the computer is turned off. Such a
type of memory is called secondary memory. In secondary memory, programs and
data are stored. It is also called auxiliary memory. It is different from primary memory
as it is not directly accessible through the CPU and is non-volatile. Secondary or
external storage devices have a much larger storage capacity and the cost of
secondary memory is less as compared to primary memory.
Use of Secondary memory
Secondary memory is used for different purposes but the main purposes of using
secondary memory are:
Permanent storage: As we know that primary memory stores data only
when the power supply is on, it loses data when the power is off. So we
need a secondary memory to stores data permanently even if the power
supply is off.
Large Storage: Secondary memory provides large storage space so that we
can store large data like videos, images, audios, files, etc permanently.
Portable: Some secondary devices are removable. So, we can easily store or
transfer data from one computer or device to another.
Types of Secondary memory
Secondary memory is of two types:
1. Fixed storage
In secondary memory, a fixed storage is an internal media device that is used to store
data in a computer system. Fixed storage is generally known as fixed disk drives or
hard drives. Generally, the data of the computer system is stored in a built-in fixed
storage device. Fixed storage does not mean that you can not remove them from the
computer system, you can remove the fixed storage device for repairing, for the
upgrade, or for maintenance, etc. with the help of an expert or engineer.
Types of fixed storage:
Following are the types of fixed storage:
Internal flash memory (rare)
SSD (solid-state disk)
Hard disk drives (HDD)
2. Removable storage
In secondary memory, removable storage is an external media device that is used to
store data in a computer system. Removable storage is generally known as disks drives
or external drives. It is a storage device that can be inserted or removed from the
computer according to our requirements. We can easily remove them from the computer
system while the computer system is running. Removable storage devices are portable
so we can easily transfer data from one computer to another. Also, removable storage
devices provide the fast data transfer rates associated with storage area networks
(SANs).
Types of Removable Storage:
Optical discs (like CDs, DVDs, Blu-ray discs, etc.)
Memory cards
Floppy disks
Magnetic tapes
Disk packs
Paper storage (like punched tapes, punched cards, etc.)
5. Hard Disk: A hard disk is a part of a unit called a hard disk drive. It is used to storing
a large amount of data. Hard disks or hard disk drives come in different storage
capacities.(like 256 GB, 500 GB, 1 TB, and 2 TB, etc.). It is created using the collection
of discs known as platters. The platters are placed one below the other. They are
coated with magnetic material. Each platter consists of a number of invisible circles
and each circle having the same centre called tracks. Hard disk is of two types (i)
Internal hard disk (ii) External hard disk.
6. Flash Drive: A flash drive or pen drive comes in various storage capacities, such as 1
GB, 2 GB, 4 GB, 8 GB, 16 GB, 32 GB, 64 GB, up to 1 TB. A flash drive is used to transfer
and store data. To use a flash drive, we need to plug it into a USB port on a computer.
As a flash drive is easy to use and compact in size, Nowadays it is very popular.
7. Solid-state disk: It is also known as SDD. It is a non-volatile storage device that is
used to store and access data. It is faster, does noiseless operations(because it does
not contain any moving parts like the hard disk), consumes less power, etc. It is a great
replacement for standard hard drives in computers and laptops if the price is low and
it is also suitable for tablets, notebooks, etc because they do not require large storage.
8. SD Card: It is known as a Secure Digital Card. It is generally used in portable devices
like mobile phones, cameras, etc., to store data. It is available in different sizes like 1
GB, 2 GB, 4 GB, 8 GB, 16 GB, 32 GB, 64 GB, etc. To view the data stored in the SD card
you can remove them from the device and insert them into a computer with help of a
card reader. The data stores in the SD card is stored in memory chips(present in the SD
Card) and it does not contain any moving parts like the hard disk.
Assigment: What are the differences between primary and secondary memories?
Solution:
Primary Memory Secondary Memory (i) Primary memory devices are semiconductor memories. (i) Secondary memory devices are magnetic, optical and electronic memories. (ii) Primary memory can be volatile as well as non-volatile. RAM is the volatile memory and ROM is the non-volatile memory, (ii) Secondary memory is always non- volatile (iii) Primary memory is more effective and interacts more quickly with the microprocessor (iii) Secondary memory is somewhat slower in interacting with the microprocessor than primary memory.
Cache Memory is a special very high-speed memory. The cache is a smaller and faster
memory that stores copies of the data from frequently used main memory locations.
There are various different independent caches in a CPU, which store instructions and
data. The most important use of cache memory is that it is used to reduce the average
time to access data from the main memory.
Characteristics of Cache Memory
Cache memory is an extremely fast memory type that acts as a buffer
between RAM and the CPU.
Cache Memory holds frequently requested data and instructions so that they
are immediately available to the CPU when needed.
Cache memory is costlier than main memory or disk memory but more
economical than CPU registers.
Cache Memory is used to speed up and synchronize with a high-speed CPU.
Cache Memory
Levels of Memory
Level 1 or Register: It is a type of memory in which data is stored and accepted
that are immediately stored in the CPU. The most commonly used register is
Accumulator, Program counter, Address Register, etc.
Level 2 or Cache memory: It is the fastest memory that has faster access time
where data is temporarily stored for faster access.
Level 3 or Main Memory: It is the memory on which the computer works
currently. It is small in size and once power is off data no longer stays in this
memory.
Level 4 or Secondary Memory: It is external memory that is not as fast as the
main memory but data stays permanently in this memory.
Cache Performance
When the processor needs to read or write a location in the main memory, it first checks
for a corresponding entry in the cache.
