Computer memory
- 1. Assignment 3: 1) Define the computer Memory. A Computer memory is just like a human brain. It is used to store data and instructions. Computer memory is the storage spacein computer where data is to be processed and instruction required for processing are stored. It is an essential element of a computer. Without its memory a computer is of hardly any use. It plays an important role in saving and retrieving data. The performance of the computer system depends upon the size of the memory. There are various units which are used to measure computer memory. They are; Bit- smallest unit of computer memory Byte- 8 bit= 1 byte Kilobyte-1024 byte= 1 kilobyte Megabyte=1024 kilobyte= 1 Megabyte Gigabyte-1024 Megabyte= 1 Gigabyte Terabyte- 1024 Gigabyte= 1 terabyte Computer memory are classified into two types as: 1. Primary Memory 2. Cache Memory 3. SecondaryMemory Primary Memory- Primary Memory is internal memory of the computer. It is also known as main memory of computer. It is a memory that holds the data and instruction on which computer is currently working It is the only type of memory which is directly accessed bythe CPU. The CPU continuously reads instructions stored in the Primary Memory and executes them. Any data that has to be operated by the CPU is also stored. The information is transferred to various locations through the Bus. It is fixed in the mother board of the computer. It is such type of memory without which a computer cannot run. It is working memory of the computer. Primary memory is of two types. They are: RAM ROM
- 2. RAM – It stands for Random Access Memory. Here data can be stored temporarily, so this type of memory is called temporary memory or volatile because when power fails the data from RAM will be Erased. The information stored in the RAM is basically loaded from the computer’s disk and includes information related to the operating system and applications that are currently executed by the processor. RAM is considered random access because any memory cell can be directly accessed if its address is known. The more RAM a computer has, the more data a computer can manipulate. RAM is further classified into two parts as: SRAM (Static RAM) DRAM (Dynamic RAM) 1. SRAM - SRAM stands for Static Random-Access Memory. The word “Static” refers that the memory retains its contents as long as the power is supplied to it so that’s why we can say this is volatile in nature. It is made of flipflops and is used for Primary storage. SRAM does not need to be refreshed periodically. SRAM is faster and more expensive than DRAM. 2. DRAM- DRAM stands for Dynamic Random-Access Memory. It also contains data only when electricity is available. It is called Dynamic because it must be constantly be refreshed and loses the data in very short time even if it continues to have power supplied to it. DRAM needs to be refreshed periodically due to this, this RAM work slower than SRAM. ROM- ROM stands for Read Only Memory. In this, the data will be furnished by the manufactures regarding the system, so this information can simply be read by the user but cannot add new data or it cannot be modified. ROM is non- volatile memory that retains data without the flow of electricity. ROM are basically classified into 3 types as: PROM EPROM EEPROM 1. PROM-PROM stands for “Programmable Read Only Memory”. In this, when the data is stored then we have no right to Chage or alter any data of it. In this the data is written by manufacturer company, even we can also purchase blank PROM chip but it can be programmed by special tool such as PROM programmers. In general, in PC’S mainly PROMis used because we don’thave to alter any data to it.
- 3. 2. EPROM-EPROMstands for “Erasable Programmable Read Only Memory”. As the word refers “erasable means we can change or erase the data. So, in EPROM we have right to change the data. In this, we can change the data with the help of ultra violet rays. EPROM is much expensive than PROM. 3. EEPROM-EEPROMstands for “Electrically Erasable Programmable Read Only Memory”. It is such type of ROM which can be erased by electrical charges. EEPROM can be erased one byte at any time rather than erasing the entire chip by ultra violet rays. Cache Memory: Caches Memory is a small-sized type of volatile memory that provides high speed data access to processorand stores frequently used computer programs, applications and data. It stores and retains data until a computer is powered up. It is smallest amount of fastest memory. It sits between normal main memory and CPU. It may be located in CPU chip or module. Working of Cache memory: The CPU initially looks in the cache for the data it needed. If the data is there, it will retrieve it and process it. If the data is not there, then the CPU accesses the system memory and then puts a copyof the new data in the cache before processing it. Next time if CPU needs to access the same data again, it will just receive the data from the caches instead of going through the whole process again. Levels of Cache memory: There are three levels of caches memory. They are as follows: Level 1 (L1 cache)-L1 is the fastest cache and usually comes within the processor chip itself. The L1 cache typically ranges in size from 8kb to 64 Kb and uses the high-speed SRAM (Static RAM) instead of the slower and cheaper DRAM (Dynamic RAM) used for main memory. It is referred to as internal caches or primary caches. Level 2 (L2 cache)-The L2 cache is larger but slower in speed than L1 cache. It stores recently accessed information. Also known as secondary cache, it is designed to reduce the time needed to accessed the data in case where data has already been accessed previously. L2 comes between L1 and RAM(Processor-L1- L2-RAM) and is bigger than the primary cache (typically 64 kb to 4 MB). Level 3 (L3 cache)-L3cache memory is an enhanced form of memory present on the mother board of Computer. L3 cache memory which is built into the
- 4. motherboard. It is used to feed the L2 cache, and is typically faster than the system’s main memory, but still lower than the L2 cache, having more than 3MB of storage in it. SECONDARYMEMORY-As we know, primary memory of a computer is temporary in nature, I.e., it does not retain its contents once the power is switched off or even if there is a temporary break in power. Thus, the primary memory is unsuitable for storing large amount of data for a longer period of time. So there arises a need for a secondary storage. Secondary storage or auxiliary memory consists of slower and less expensive device that communicate with CPU via main memory. The secondary memory stores the data and keep it even when the power fails. It is used to save large data or program or other information. Some of the main Secondary memory are: 1. Magnetic Disk 2. Floppy Disk 3. Hard Disk 4. Optical Disks 1. Magnetic Disk-Magnetic Disk is type of secondarymemory which is a flat disc covered with magnetic coating to hold information. It is used to store various programs and files. The polarized information in one direction is represented by 1, and vice versa. The direction is indicated by 0. Magnetic disk is less expensive than RAM and can store large amounts of data, but data access rate is slower than main memory because of secondarymemory. Data can be modified or can be deleted easily in the magnetic disk memory. It also allows random access of data. 2. Floppy Disk-FloppyDisk is a small plastic disk, coated with a magnetic material and enclosed in a square plastic casing. It is used to transfer small amount of data between the computers. They are also used to hold back-up copies of the data and program. A typical 3.5-inch floppy disk holds 1.44 MB of data. The floppy disk has the disadvantages of limited storage, slow speed and low reliability compared to other storage devices. 3. Hard Disk-Hard Disk is a mass storage device consisting of one or more platters. Each platter is a thin, circular metal plate coated on both sides with a magnetic material. It is sealed inside a metal caseto prevent any foreign material from getting inside, which causes head crash. It provides faster
- 5. access to data and are capable of storing large quantity of data. Today’s computers typically come with high storage capacity hard disk. 4. Optical Disk-Opticaldisk is a glass or plastic disk coated with reflecting medium. A very fine laser beam is projected on the reflecting surface to read data from the disk. By detecting the light intensity reflected from the surface, the information stored on the disk can be accessed. The optical Disk are commonly used for video and audio applications. The storage capacity of laser disk is very high and access of information is very fast. CD-ROM (CompactDisk Read Only Memory) and DVD (Digital Versatile Disk) are the common type of optical disks. ==================================================