Computer Notes !Chapter- 8 Memory Organization ! memory system ! Random Access Memory (RAM) ! Kinds of RAM ! Dynamic RAM (DRAM) ! Static RAM(SRAM) ! Video RAM ! Flash RAM ! Read Only Memory (ROM) ! Kinds of ROM ! ROM ! Video RAM ! Flash RAM ! Read Only Memory (ROM) ! Kinds of ROM ! ROM ! Programmable ROM(PROM) ! Erasable Programmable ROM(EPROM) ! Electrically Erasable Programmable ROM (EEROM) !
A memory system is a very simple system exhibits a wide range of technology types.
Random Access Memory (RAM):
RAM is the place in a computer where the operating system, application programs, and data in current usage are kept so that they can be quickly accessed by the processor. RAM reads and writes faster than the other kind of storage in a computer like the hard disk, and CD-ROM. However , the data in RAM stored temporarily till the computer is running. when the power of computer cut then RAM loses its data when you switch on your computer, the operation system and other files are once again loaded into RAM, usually from your hard disk
RAM is known as 'Random Access Memory' because any storage location can be accessed randomly. RAM is organized and controlled in a way that enables data to be stored and retrieved directly to specific locations. In addition to disk, floppy disk, and CD-ROM storage, another important from of storage is read-only memory (ROM), a more expensive kind of memory that retains data when the computer is turned off. Every computer comes with a small amount of ROM that holds just enough programming so that the operating system can be loaded into RAM each time the computer is turned on.
Kinds of RAM :
RAM is of only two kinds i.e Dynamic and Static, which stores every kind of data and makes it quickly accessible to a microprocessor . However there is some spacial RAM that can be both dynamic and static like video RAM. which stores data intended for the display screen, enabling images to get display faster.
Dynamic RAM (DRAM) :
Dynamic RAM uses a kind of capacitor that needs frequent power refreshing to retain its charge, Because reading a DRAM discharges its contents, a power refresh is required after each read. DRAM must be refreshed about every 15 microseconds. DRAM is the least expensive kind of RAM Synchronous with the clock speed that the microprocessor is optimized. Synchronous tends to increase the number of instructions that the processor can perform in a given time. The speed of SDRAM is rated in MHz rather than in nanoseconds (ns). This makes it easier to compare the bus speed and the RAM chip speed. You can convert the RAM clock speed to nanosecond (ns). by dividing the chip speed into 1 billion as (which is equal to one second ) For example. an 83 MHz RAM would be equivalent to 12 ns.
Static RAM(SRAM)
Static RAM as the more expansive. requires four time the amount of space for a given amount of data than dynamic RAM. Unlike , dynamic RAM, it does not need to be power-refreshed and is there four faster to access. One source gives a typical access time as 25 nanoseconds in contrast to an access time of 60 nanoseconds for dynamic RAM.
Video RAM:
Video RAM as the name signifies is a general form of RAM used to store image data for the video display monitor. All types of video RAM are special arrangement of dynamic RAM (DRAM). Video RAM is really a buffer between the processor and the display monitor and is often known as the frame buffer When image are to be sent to the display, they are first read by the processor and then written to video RAM. From video RAM (the frame buffer): the data is converted by a RAM digital-to-analog converter (RAMDAC) into analog signals that they are sent to the display presentation mechanism such as a cathode ray tube (CRT). Usually, video RAM comes in a 1 or 2 megabyte package and is located on the video or graphics in the computer.
Flash RAM:
Flash RAM sometimes called flash memory is a type of constantly powered non-volatile memory that can be erased and reprogrammed in units of memory called blocks. it is a variation of electrically erasable programmable read-only memory (EEPROM), which unlike flash memory, is erased and rewritten at the byte label. Flash memory is erased and rewritten at the byte label. Flash memory is often used to hold control code such as the basic input/output system (BIOS) in a personal computer. when BIOS need to hold to be changed or rewritten , the flash memory can be written in block (rather than type) size, making it easy to update . On the other hand flash memory is not useful as random access memory (RAM) because RAM needs to be addressable at the byte (not the block) level. Flesh memory drives its name because the microchip is organized in a way so that a section of memory cells are erased in a single action or 'flash' Flash memory is used in digital cellular phones, digital cameras, LAN switches, PC cards for notebook computers, digital setup boxer, embedded controllers, and other devices.
Read Only Memory (ROM) :
Read only memory is most commonly used to store system level program that to be available to the PC at all time ? The most common example is the system BIOS program, which stored in a ROM and used to boot up the system. When you first turn on the PC the system memory is empty , so there has to be something for the PC use when it starts up . These programs are stored at the manufacturing time and could not be changed later on .
Kinds of ROM :
The contents of a ROM cannot be changed, there are times when being able to change the contents of a ROM becomes very useful. There are several ROM variants that can be changed under certain circumstance these can be thought of as mostly read only memory . The following are the different types of ROMs with a description of other relative modifiability.
Video RAM :
Video RAM as the name signifies is a general form of RAM used to store image data for the video display monitor . All types of video RAM are special arrangement of dynamic RAM(DRAM). Video RAM is really a buffer between the processor and the display monitor and is often known as the frame buffer. When image are to be sent to the display, they are first read by the processor and then written to video RAM .From video RAM (the frame buffer): the data is converted by a RAM digital to-analog converter (RAMDAC) into analog signals that they are sent to the display presentation mechanism such as a cathode ray tube (CRT) . Usually, video RAM comes in a 1 or 2 megabyte package and is located on the video or graphics card in the computer.
Flash RAM :
Flash RAM sometimes called flash memory is a types of constantly powered non-volatile memory that can be erased and reprogrammed in units of memory called blocks. it is a variation of electrically erasable programmable read-only memory (EEPROM), which unlike flash memory, is a erased and rewritten at the byte label . Flash memory is erased and rewritten at the byte label. Flash memory is often used to hold control code such as the basic input/output system (BIOS) in a personal computer. When BIOS needs to be changed or rewritten, the flash memory can be written in block (rather than type) size, making it easy to update. On the other hand flash memory is not useful as random access memory (RAM), because RAM needs to be addressable at the byte (not the block) level.
Flesh memory drives its name because the microchip is organized in a way so that a section of memory cells are erased in a single action or 'flash' Flash memory is used in digital cellular phones, digital cameras, LAN switches , PC cards for notebook computer digital setup boxes, embedded controllers, and other devices.
Read Only Memory (ROM) :
Read only memory is most commonly used to be available to the PC at all times? The most common example is the system. BIOS program, which stored in a ROM and used to boot up the system. When you first turn on the PC the system memory is empty. so there has to be something for the PC to use when it starts up. These programs are stored at the manufacturing time and could not be changed later on.
Kinds of ROM) :
The contents of a ROM is cannot be changed , there are times when being able to change the contents of a ROM becomes very useful. There are several ROM variants that can be changed under certain circumstance these can be thought of as mostly read only memory . The following are the different types of ROMs with a description of other relative modifiability .
ROM :
A regular ROM is constructed from hard-wired logic , encoded in the silicon itself to a processor. it is designed to perform a specific function and cannot be changed. This is inflexible and so regular ROMs are used generally for programs that are static (not changing often) and mass produced .
Programmable ROM(PROM) :
A type of ROM that can be programmed using special equipment, it can be written to, but only once. it is useful for companies that make their own ROMs for the software they write . This is because when they change their code they can create new PROMs without requiring expensive equipment. This is similar to the way a CD-ROM recorder works by letting you create or write programs onto blank one and the letting you read from them many times, in fact programming a PROM is also called burning, just like burning a CD-R, and it is comparable in terms of its flexibility
Erasable Programmable ROM(EPROM)
An EPROM is a ROM that can be erased and reprogrammed. A little . glass window is installed at the top of the ROM package, through which you can actually see the ship that holds the memory. Ultraviolet light of a specific frequency can be shined through this window for a specific period of time, which will erase the EPROM and allow it to be reprogrammed again. Obviously , EPROM is much more useful than a regular PROM, but it does require the erasing light. This technology is analogous to a reusable CD-ROW (CD Read Write).
Electrically Erasable Programmable ROM(EEPROM).
The next level of erase ability is the EEPROM, which can be erased under software control. This is the most flexible type of ROM, and is now commonly used for holding BIOS programs. The term flashes BIOS or doing BIOS upgrade by flashing refers to reprogramming the BIOS EEPROM with a special Software Program.
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