![1
Digital Electronics
[EC282]
Topic: Semiconductor Memories â Program and Data Memory, Memory
Types and Terminology, SRAM, DRAM](https://image.slidesharecdn.com/5a-250607123116-8b6735cb/85/5A-Semiconductor-Memories-Part-I-4-pptx-1-320.jpg)
5A. Semiconductor Memories Part I (4).pptx
- 1. 1 Digital Electronics [EC282] Topic: Semiconductor Memories â Program and Data Memory, Memory Types and Terminology, SRAM, DRAM
- 2. Digital Electronics System ⢠There are 3 important classes of devices that are used to build a digital electronics systems: â Memory devices â Microprocessor â Logic Devices 12-05-2022 DE â Semiconductor Memories â Prof. T. L. Singal 2
- 3. Memory 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 3 ⢠A memory is just like a human brain. It is used to store data and instruction in binary form. ⢠The memory is divided into large number of small parts. Each part is called a cell. Each location or cell has a unique address which varies from zero to memory size minus one. ⢠For example if computer has 64k words, then this memory unit has 64 * 1024 = 65536 memory location. The address of these locations varies from 0 to 65535. ⢠Memory is primarily of two types â Internal Memory â cache memory and primary/main memory â External Memory â magnetic disk / optical disk etc.
- 4. Memory structure 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 4
- 5. ⢠The Primary Memory is also known as system memory, whereas the Secondary Memory is called the Storage. ⢠The Secondary memory is physically located within a distinct storage devices, such as an HDD. ⢠The secondary memory is connected to the computer either directly or over a network. As you can assume from their large sizes, the cost per GB of secondary memory is quite low. However, the speed of read/write operations is also considerably slower. ⢠The Primary memory is located close to the Central Processing Unit on the motherboard. This proximity enables the CPU to access information 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 5 immediately. The processor thus gets information needed, without much delay. ⢠These are expensive but very fast. an immediate response to any
- 6. CPU access to memory 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 6
- 7. Characteristics of Memory Hierarchy from top to bottom ⢠Capacity in terms of storage increases. ⢠Cost per bit of storage decreases. ⢠Frequency of access of the memory by the CPU decreases. ⢠Access time by the CPU increases. 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 7
- 8. 8 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal
- 9. RAM 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 9 ⢠The form of integrated circuits that allow the stored data to be accessed in any order, i.e. at random. Regardless of the memory location that was last accessed. ⢠Volatile memory, requires power to maintain the stored information ⢠RAM generally store a bit of data in either the state of a flip-flop, as in SRAM (static RAM), or as a charge in a capacitor (or transistor gate), as in DRAM (dynamic RAM). ⢠A typical computer usually has about 8 GB of RAM. Newer systems can boast of having up to 64GBs. If you are using programs and software which take up a lot of space, such as Adobe, Photoshop, etc. you might need a more significant RAM Memory. But, even if you have sufficient
- 10. SRAM and DRAM? 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 10 Factors SRAM DRAM Number of transistors 6 Transistors 1 Transistor Charge Leakage Not evident A lot of discharge happens, thus there is a refresh circuitry Speed Quite fast Comparatively slower Power Consumption Low High Space it occupies Less space More space Cost Expensive Cheap Density Less dense Denser Application Cache Memory Main memory
- 11. Non-volatile 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 11 Retains the stored information even when not powered Electrically Addressed ⢠ROM â MROM â PROM â EPROM â EEPROM Flash memory (NOR and NAND) Mechanically Addressed System Tape Hard disk Optical disk (CD, DVD) Magnetic Disk (Floppy Disk)
- 12. ROM (Read-only memory) ⢠It is also known as firmware. ⢠It is an integrated circui t dat a programmedwith specific when it is manufactured. ⢠ROM chips are used not only in computers, but in most other electronic items as well. 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 12
- 13. PROM ⢠Programmable read-only memory (PROM) or field programmable read-only memory (FPROM) is a form of digital memory where the setting of each bit is locked by a fuse or antifuse. Such PROMs are used to store programs permanently. The key difference from a strict ROM is that the programming is applied after the device is constructed. ⢠Creating ROM chips totally from scratch is time-consuming and very expensive in small quantities. For this reason, mainly, developers created a type of ROM known as programmable read-only memory (PROM). Blank PROM chips can be bought inexpensively and coded by anyone with a special tool called a programmer. 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 13
- 14. EPROM Erasable programmable read-only memory ⢠It is an array of floating-gate transistors individually programmed by an electronic device that supplies higher voltages than those normally used in electronic circuits. Once programmed, an EPROM can be eâ˘rased only by exposing it to strong ultraviolet light. ⢠Working with ROMs and PROMs can be a wasteful business. Even though they are inexpensive per chip, the cost can add up over time. Erasable programmable read-only memory (EPROM) addresses this issue. EPROM chips can be rewritten many times. Erasing an EPROM requires a special tool that emits a certain frequency of ultraviolet (UV) light. EPROM's are configured using an EPROM programmer that provides voltage at specified levels depending on the type of EPROM used. ⢠EPROM's are easily recognizable by the transparent fused quartz window in the top of the package, through which 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 14
- 15. EEPROM 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 15 (Electrically Erasable Programmable Read Only Memory) ⢠Though EPROMs are a big step up from PROMs in terms of reusability, they still require dedicated equipment and a labor-intensive process to remove and reinstall them each time a change is necessary. Also, changes cannot be made incrementally to an EPROM; the whole chip must be erased. Electrically erasable programmable read-only memory (EEPROM) chips remove the biggest drawbacks of EPROMs. In EEPROMs: ⢠The chip does not have to removed to be rewritten. ⢠The entire chip does not have to be completely erased to change a specific portion of it. ⢠Changing the contents does not require additional dedicated equipment.
- 16. Difference b/w RAM and ROM? 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 16 Factors RAM ROM Nature of working Volatile memory â needs power supply Non-volatile memory â doesnât need power Speed Fast Not as fast as RAM Storage Capacity High Capacity, ranging from 1 to 256 GB Low Capacity of about 4-8MB Space it occupies RAM data takes a lot of space RAM takes up less space Cost More expensive Affordable Data Can be altered anytime Cannot be modified/limited changes permitted but not done easily Application Used to store program codes which CPU needs immediately Used to store booting instructions or firmware coding
- 17. Difference between EPROM and EEPROM? 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 17 Factors EPROM EEPROM The medium of erasure of data UV Light is used to erase data An electrical signal is used to delete data Updating is done by Need to eject the EPROM chip to update the data No ejection is required for reading or erasing the data Timeline of technology This is an older technology. This is a newer technology. Design on the case Has a transparent quartz crystal window on the top The memory is entirely enclosed in an opaque case. Preceded by EPROM is the updated version of the PROM. EEPROM is the updated version of the EPROM. Time for erasing Erasing the contents takes about 15- 20 minutes. Erasing the contents takes about 5ms only. Programming Technique A hot electron injection technique is used for reprogramming the EPROM. The tunnel effect is used for programming the EEPROM.
- 18. Flash Memory 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 18 ⢠Flash memory is a non-volatile memory used for storage purposes and transferring information between devices. ⢠It is a developed version of the EEPROM memory, where data can be electronically programmed as well as erased. ⢠In Flash memory, the data is block-erasable. Whereas in EEPROM, the data is byte-erasable. ⢠The Flash memory is similar to the standard MOSFET, except that the transistor has two gates and not one. ⢠Flash memory is reasonable to purchase than conventional EEPROM memories and does not require batteries for solid-state storage. ⢠It has high-speed access time and has excellent resistance to kinetic shock. ⢠These memory sticks are incredibly durable, with the ability to withstand intense pressure or extreme temperatures. ⢠Flash memory is often found in USB drives, iPods, MP3 players, and many more portable electronics.
- 19. Cache Memory g ones too, in case of future referencing) into the cach The Cache memory, also known as the CPU Memory, is a fast-operating static RAM (SRAM) that can be more easily accessed by the processing unit as compared to regular RAMs. Since it is designed using the SRAM, it is more expensive. It is also faster than other memories. The cache access time is as less as one clock cycle, whereas the main memory access requires several clock cycles. What is a cache hit and a cache miss? When the main memory address needs to be accessed by the processor for reading/write operations, we first go to the cache memory and search for a copy of the location. If we find it, it is a cache hit, and the processor can continue with the operations immediately. However, if the copy is absent, it is referred to as a cache miss, and we must first read this address (with some neighborin e memory. What are the different types of cache memories? â˘Primary Cache â Most of the cache is located together close to the CPU processor itself on the same die. This is called the Primary Cache. â˘Secondary Cache â This can be considered as an extension of the cache memory located on a separate chip on the computer motherboard, but close to the CPU. 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 19
- 20. Memory units 5/12/2022 DE - Semiconductor Memories - Prof T. L. Singal 20 S.No. Unit & Description 1 Bit (Binary Digit) A binary digit is logical 0 and 1 representing a passive or an active state of a component in an electric circuit. 2 Nibble A group of 4 bits is called nibble. 3 Byte A group of 8 bits is called byte. A byte is the smallest unit, which can represent a data item or a character. 4 Word A computer word, like a byte, is a group of fixed number of bits processed as a unit, which varies from computer to computer but is fixed for each computer. The length of a computer word is called word-size or word length. It may be as small as 8 bits or may be as long as 96 bits. A computer stores the information in the form of computer words. S.N o. Unit & Description 1 Kilobyte (KB) 1 KB = 1024 Bytes 2 Megabyte (MB) 1 MB = 1024 KB 3 GigaByte (GB) 1 GB = 1024 MB 4 TeraByte (TB) 1 TB = 1024 GB 5 PetaByte (PB) 1 PB = 1024 TB Memory unit is the amount of data that can be stored in the storage unit. This storage capacity is expressed in terms of Bytes. The following table explains the main memory storage units â
- 21. Thanks!