TOPIC : Memory Classification Satish Pradhan Dnyanasadhana college, Thane Subject-Physics APPLIED COMPONENT-II Class- T. Y. B. Sc. SEM-VI TOPIC : Memory Classification Presented By Ms. Namrata A. Singh Dept. of Physics

Memory Classification. Contents Introduction. Memory Classification. Memory Types.

Introduction It refers to the physical devices used to store programs (sequences of instructions) or data (e.g. program state information) on a temporary or permanent basis for use in a computer or other digital electronic devices. It is required for storage and subsequent retrieval of the instructions and data. It exhibits a wide range of technology and types.

Memory Internal Memory Cache Memory Main Memory Secondary Memory Internal Memory: This is where actual processing is done which constitutes of small set of high speed registers. Primary Memory (Main Memory): It is a large memory which is accessed directly by a processor. It is mainly based on integrated circuits. Secondary Memory: It is a large memory which is slower than primary memory. It can be used as overflow memory incase the main memory capacity has exceeded. Internal Memory Cache Memory Main Memory Secondary Memory

Memory Classification

Memory Types Memories are classified on the basis of several attributes, but in general they are classified on the basis of their access time. They are as follows: Random Access Memory (RAM) Sequential Access Memory (SAM) Based on their read and write time, RAMs are further classified as, Read Only Memories (ROMs) Read Mostly Memories (RMMs) Read Write Memories (RWMs)

READ ONLY MEMORY (ROM) It is a non-volatile memory. It retains the stored information even if the power is turned off. It is equivalent to a group of registers each permanently storing a word. Four Types of ROMs are presently available: Masked ROM Programmable ROM Erasable Programmable ROM Electrically erasable programmable ROMs

Read Only Memory (ROM):- Rom is non-volatile memory. That is it retains the stored information even if the power is turned off. The manufacturer of ROM design the MOSFET ( Metal–Oxide– Semiconductor Field-Effect Transistor is a transistor used for amplifying or switching electronic signals.) memory cell interims of diode matrix . Diodes connect the horizontal lines to vertical lines . Binary addresses ranging from 000 to 111.The required information is stored by diodes as 0’s and 1’s .The presence of diode represent 1 while its absence represent 0.When a register is selected , the voltage of that line goes high, and the corresponding output lines, where diodes are connected go high .for example, when the memory register 100 is selected, the data byte 10101010 can be read at the data lines D7......D0. For example 3 address lines can select (23)8 memory locations 8 address lines can select 28 = 256 ( 0 to 255)locations.

Masked ROM Mask ROM (MROM) is a type of read-only memory (ROM) whose contents are programmed by the integrated circuit manufacturer (rather than by the user). The terminology "mask" comes from integrated circuit fabrication, where regions of the chip are masked off during the process of photolithography. The main advantage of mask ROM is its cost. Per bit, mask ROM is more compact than any other kind of semiconductor memory. Since the cost of an integrated circuit strongly depends on its size, mask ROM is significantly cheaper than any other kind of semiconductor memory. However, the one-time masking cost is high and there is a long turn-around time from design to product phase. Design errors are costly: if an error in the data or code is found, the mask ROM is useless and must be replaced in order to change the code or data. It is economical only when production in thousands is needed.

Programmable ROMs (PROMs) It is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. They are a type of ROM (read-only memory) meaning the data in them is permanent and cannot be changed. PROMs are used in digital electronic devices to store permanent data, usually low level programs such as firmware. The key difference from a standard ROM is that the data is written into a ROM during manufacture, while with a PROM the data is programmed into them after manufacture. PROMs are manufactured blank and, depending on the technology, can be programmed at wafer, final test, or in system. Blank PROM chips are programmed by plugging them into a device called a PROM programmer. Once this is done the programming is permanent.

Erasable Programmable ROMS (ROMs) ROMs that allow reprogramming are called erasable programmable ROMs. The information stored in EPROMs can be erased by exposing the memory to ultraviolet light through the quartz window available on the chip for about 20 min. The UV light causes stored charge to leak off and lets you reprogram. The only disadvantage is that the contents of entire EPROM will be lost. It is used in product development and experimental projects.

Electrically Erasable Programmable ROMs (EEPROMs) It uses MOS circuitry similar to EPROMs. Data is stored as charge or on an insulated layer (of thickness 200 angstrom) on an insulated floating gate in the MOS device. A voltage of 20 to 30 V can be used to move charges across the thin barrier in either direction for programming or erasing. By adding a tristate gates to the data lines of memory we can obtain a tristated output. Enable line is provided to control the output.

Random Access Memory (RAM) It is also called as read write memory. Today, random-access memory takes the form of integrated circuits. RAM is normally associated with volatile types of memory (such as DRAM memory modules), where stored information is lost if the power is removed, although many efforts have been made to develop non-volatile RAM chips. Semiconductor RAMs are of two types. Static Dynamic

Static RAM Static random-access memory (SRAM or static RAM) is a type of semiconductor memory that uses bistable latching circuitry to store each bit. The term static differentiates it from dynamic RAM (DRAM) which must be periodically refreshed. SRAM exhibits data remanence, but it is still volatile in the conventional sense that data is eventually lost when the memory is not powered. They have memory cells that are similar to common flip-flop and it stores bit as voltage.

Dynamic RAM Dynamic random-access memory (DRAM) is a type of random-access memory that stores each bit of data in a separate capacitor within an integrated circuit. The capacitor can be either charged or discharged; these two states are taken to represent the two values of a bit, conventionally called 0 and 1. The advantage of DRAM is its structural simplicity: only one transistor and a capacitor are required per bit, compared to four or six transistors in SRAM. This allows DRAM to reach very high densities. The transistors and capacitors used are extremely small; billions can fit on a single memory chip.

D RAM

Bubble Memories Bubble memory is a type of non- volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each storing one bit of data. They are non volatile in nature and can store large amount of data.

Flash Memory Flash memory is an electronic non-volatile computer storage medium that can be electrically erased and reprogrammed. The only difference between the flash memory and EEPROM is in the erasure procedure. Flash memory must be erased either in its entirety or the sector/block level. Examples: Main memory, Memory cards, Solid State Drives, USB flash drives.