Semiconductor Memories: RAM (Random Access Memory) Explained

Summary

Highlights

• Semiconductor memories, including RAM, use semiconductor technology for digital data storage 📂.
• Flip-flops are basic memory elements storing one bit, while registers combine multiple flip-flops 📏.
• RAM provides the CPU with necessary storage space for program and OS processes during operations 🎛️.
• RAM's architecture allows uniform access time to any memory word, leading to its 'random' nature 🔄.
• The size of RAM depends on the number of words and their length, expressed in kilobytes, megabytes, or gigabytes 💾.

Key Takeaways

• RAM is volatile meaning it loses its data when powered off 🔌.
• RAM allows for both read and write operations unlike ROM which is mostly read-only 📖.
• The architecture of RAM permits equal time access (random access) to all memory words ⏲️.
• Memory size can be calculated by multiplying the number of words and word length 🧮.
• Decoders are essential in RAM for selecting specific words based on address lines 🔑.

Overview

Chapters

• 00:00 - 00:30: Introduction to Semiconductor Memories The chapter introduces semiconductor memories, storage devices that use semiconductor technology for digital data storage. It emphasizes the widespread use of these memories in electronic devices and focuses specifically on RAM.
• 00:30 - 01:00: Basic Memory Elements: Flip-Flops and Registers This chapter focuses on basic memory elements within digital systems, specifically flip-flops and registers. Flip-flops are the fundamental memory component, capable of storing one bit of information. When several flip-flops are combined, they form a register that can store multiple bits, typically in multiples such as 8, 16, 32, or 64 bits.
• 01:00 - 01:30: Role of Registers in CPUs This chapter discusses the role of registers in CPUs, highlighting their function of storing the data and instructions actively being processed by the CPU. It emphasizes that registers can hold only a limited number of bits and that CPUs have a restricted number of registers.
• 01:30 - 02:00: Main Memory: RAM and ROM The CPU requires a fast and large storage, measured in MB or GB, to store programs and operating system processes that are frequently accessed during operation. This storage is known as the main memory. Main memory is categorized into two types: RAM (Random Access Memory) and ROM (Read-Only Memory).
• 02:00 - 02:30: Characteristics of RAM and ROM The chapter discusses the characteristics of RAM (Random Access Memory) and ROM (Read-Only Memory). It explains that ROM is primarily used for reading content as it is a read-only memory, although some modern ROMs allow occasional write operations. In contrast, RAM permits both read and write operations.
• 02:30 - 03:00: Understanding RAM Architecture The chapter 'Understanding RAM Architecture' introduces the concept of RAM (Random Access Memory) architecture, focusing on its fundamental properties and operations. It begins with a discussion on basic memory terminologies, emphasizing that any memory unit comprises storage cells and digital circuits for data transfer. Each storage cell in a memory unit is responsible for storing a single bit of information.
• 03:00 - 03:30: Concept of Word in Memory The concept of 'word' in memory refers to how information is stored or retrieved in groups of bits, known as words. Different types of memory can have varying word lengths, such as 8, 16, or 32 bits. The key concept is that information is accessed in full, meaning all bits of a word are accessed simultaneously. This ability depends on the architectural design of the RAM, which dictates the time required to access any word.
• 03:30 - 04:00: Random Access in RAM Random Access Memory (RAM) allows data to be transferred to or from memory in a constant amount of time, regardless of the location of the data. This uniformity in access time justifies its name. In RAM, information is stored as binary data - ones and zeros. Importantly, RAM is a volatile memory, meaning it retains information only while powered on. Once the power is switched off, all stored data is lost.
• 04:00 - 04:30: Volatility of RAM RAM is a type of volatile memory, meaning that information stored in RAM is lost when the power is turned off.
• 04:30 - 05:00: RAM Block Diagram and Addressing The chapter 'RAM Block Diagram and Addressing' discusses the structure and addressing mechanism of RAM. It explains that the address of a RAM word is represented in binary form, where the first word has an address of ten 0's (0 in binary) and the last word has an address of ten 1's (1023 in binary). To access words in RAM, a 10-bit address line is utilized, indicating the specific location in RAM to be accessed. Generalizing, if RAM consists of 2^k words, then k address lines are required to access any word in the RAM.
• 05:00 - 05:30: Address Lines and Word Length The chapter addresses the concept of address lines and word length in RAM architecture. It explains that the number of required address lines is determined by the expression log(m) to the base 2, where m represents the total number of words in the RAM. Additionally, the chapter outlines that each word comprises n bits, indicating that n output lines are necessary to read data from a specific word.
• 05:30 - 06:00: Reading and Writing in RAM This chapter explains the process of reading and writing data in RAM. It details the necessity of having n input lines for writing data, and the use of the same data lines for both reading and writing. The chapter explores how read and write control signals determine whether data is written to or read from the memory, thus defining the data flow direction.
• 06:00 - 06:30: Calculating RAM Size In this chapter, the process of reading from and writing to RAM is explained. During a read operation, data is fetched from the RAM and sent to the CPU. Conversely, during a write operation, data comes from the CPU to be stored in RAM. The address line determines the specific location for data read/write actions. Control signals, specific addresses, and data inputs must be applied in a precise order to successfully read from or write to RAM.
• 06:30 - 07:00: Memory Size Units: Kilobytes, Megabytes, Gigabytes In this chapter, the core focus is on understanding the basic concepts of memory size units in computing, specifically RAM. It outlines the fundamental relationship between the total number of words in the memory and the word length, explaining that the size of the memory (RAM) can be calculated by multiplying these two parameters. The chapter provides an example, illustrating how a RAM with 1024 words and a certain word length can define its size. This sets the groundwork for future discussions on read and write operations within memory systems.
• 07:00 - 07:30: Address Decoding and Decoder Role The chapter explains the concept of address decoding in relation to memory size. It describes a scenario where if a word in memory is 16 bits, the RAM size is 2^10 times 16 bits. Since 1 byte equals 8 bits, 16 bits can be considered as 2 bytes, making the total memory size 2^10 times 2 bytes, which equals 2 kilobytes. The explanation highlights the relationship between bits, bytes, and kilobytes in digital systems.
• 07:30 - 08:00: Closing Remarks and Next Steps This chapter discusses the representation of data sizes in computing, using powers of 2. It explains the meaning behind common symbols such as 'k' for kilo, 'M' for Mega, and 'G' for Giga. The chapter illustrates how these symbols correspond to 2 to the power of 10, 20, and 30 respectively. Moreover, the text provides examples of RAM size calculations using these notations.

Semiconductor Memories: RAM (Random Access Memory) Explained Transcription

• 00:00 - 00:30 Hey friends, welcome to the YouTube channel ALL ABOUT ELECTRONICS. So in this video and in the upcoming videos, we will learn about the semiconductor memories. So this semiconductor memory refers to the storage devices that use the semiconductor technologies to store the digital data. So these memories are widely used in the various electronic devices. So in this video, we will talk about the one such memory that is known as the RAM.
• 00:30 - 01:00 So in digital systems, if we talk about the memories, then we know that the flip-flop is a very basic memory element which can store the one bit of information. And when we combine multiple such flip-flops together, then that is called the register. So if we have an n-bit register, then it can store the n-bit of data. So typically, the size of the register is in multiple of the 8 bits. Like 8 bits, 16 bits, 32 bits or 64 bits.
• 01:00 - 01:30 So every digital system consists of several registers. For example, if we see the CPU of any processor, then it also contains several registers. And these registers store the data and the instruction which is currently being processed by the CPU. But as you know, these registers can store only up to a few bits of information. And we also know that the CPU consists of only a handful of such registers.
• 01:30 - 02:00 That means the CPU needs a larger storage, like in MB or GB, which is fast enough. And it can also store the programs or OS processes, which will be required by the CPU during the operation. So this memory, which the CPU frequently accesses during the operation, is known as the main memory. So there are two types of main memory, that is the RAM and the ROM. So this RAM stands for Random Access Memory, and this ROM stands for Read-Only Memory.
• 02:00 - 02:30 So as its name suggests, this ROM is the read-only memory, meaning that we can only read the content of this memory, but we cannot write. So nowadays, the ROMs which are available in the market is mostly a read-only. Meaning that mostly it can be used for reading the content of the memory, but it is also possible to perform the occasional write operations. On the other hand, if you see the RAM or this Random Access Memory, then we can perform both read as well as write operations.
• 02:30 - 03:00 So in this particular video, we will only talk about the RAM. So before we understand more about this RAM, first let us understand some basic terminologies related to the memories. So in general, if we see any memory unit, then it is a collection of the storage cells. And along with that, it also consists of the digital circuit to transfer the information in and out from the memory unit. So this each storage cell in the memory is storing the one bit of information.
• 03:00 - 03:30 Now whenever the information is stored or retrieved from the memory, then these operations are carried out in the group of bits. And this group of bits are known as the word. So these different memories can have different word lengths. That means the one word may contain the 8 bits, 16 bits or even 32 bits. That means whenever the information is accessed from the memory, then all the bits of the word will be accessed simultaneously. Now the architecture of the RAM is such that the time required to access any word in the
• 03:30 - 04:00 memory is the same. That means if you want to transfer the information to or from the random word in the memory, then it will require the same amount of time. And that is why this memory is known as the Random Access Memory. So all these words in the RAM contain the information in 1's and 0's. Now this RAM is the volatile memory. Meaning that the information stored in the memory will remain as it is until it is powered up. And as soon as we switch off the power, then the information which is stored in the memory
• 04:00 - 04:30 will get lost. That means this RAM is the volatile memory. So now let's see the basic block diagram of this RAM. So any random access memory consists of the specific number of words in the memory. Like I said, the word is the group of bits. So each word in the RAM will be assigned the specific address. For example, if one RAM consists of a total of 1024 words, then if we see the address of the first word, then in the decimal that is equal to 0.
• 04:30 - 05:00 And if we see the address of the last word, then that will be equal to 1023. So in the binary, the address of the first word will be equal to ten 0's, while the address of the last word will be equal to ten 1's. And as you can see, if we want to access all these words, then we will require the 10 address lines. So this 10-bit address on this address line will tell us what location in the RAM we want to access. So in general, if the RAM consists of 2^k words, then to access these words, it requires the
• 05:00 - 05:30 k address lines. That means the required number of address lines should be greater than or equal to log (m) to the base 2, where here m is the number of words in the RAM. Now let's say, each word in the RAM is of n bits, or in other words, the word length is equal to n bits. That means when we want to read the data from the specific word, then we will require the n output lines.
• 05:30 - 06:00 And similarly, when we want to write the data in the word, then we will require the n input lines. Now, typically, instead of having the separate data lines for reading and writing in the memory, the same data lines are used for reading and writing. So depending on the read and write control signals, either data will be written on the RAM, or it will be read from the memory. That means these read and write control signals will decide the direction in which this data from the memory will go.
• 06:00 - 06:30 So during the read operation, the data from the RAM will be fetched and it will go as an output towards the CPU. While in case of the write operation, from the CPU, the data will come towards the RAM and it will be stored in the RAM. And this data on the address line will decide on which location in the RAM this data will be written or read from. So to read or write the data in the RAM, we need to apply the control signal, the specific address on the address line, as well as the data input in the specific order.
• 06:30 - 07:00 So in the next video, we will see that how these read and write operations are performed. But this is the basic plot diagram of the RAM. So now, if you know the total number of words in the memory, and you also know the word length, then we can easily find the size of the memory. That means the size of the RAM is equal to the total number of words in the RAM multiplied by the word length. So for example, if the one RAM has 1024 words, or the 2 to the power 10 words, and the length
• 07:00 - 07:30 of the word is equal to 16 bits, then we can say that the size of the RAM is equal to 2 to the power 10 times 16 bits. Now we know that the 1 byte is equal to 8 bits. That means here the 16 bits is equal to 2 bytes. So we can say that the size of the memory is equal to 2 to the power 10 times 2 bytes. That is equal to 2 kilobytes. So typically in the memories, or in general in digital systems, this 2 to the power 10
• 07:30 - 08:00 is shown by the symbol k, and that corresponds to kilo. Likewise, this 2 to the power 20 is shown by the symbol M, and that corresponds to Mega. And likewise, this 2 to the power 30 is shown by the symbol G, which corresponds to the Giga. That means in this case, the size of the RAM is equal to 2 kilobytes. So similarly, in another RAM, if the total number of words is equal to 2 times 2 to the power 20, and the word length is equal to 32 bits, then the size of the RAM is equal
• 08:00 - 08:30 to 2 times 2 to the power 20 words times 32 bits. Now we know that the 1 byte is equal to 8 bits. That means here this 32 bits corresponds to 4 bytes. And we know that this 2 to the power 20 corresponds to M. So we can say that the total size of the RAM is equal to 8 megabytes. So in this way, we can easily find the size of any RAM. Now so far we have seen that by applying a particular address on the address line, we
• 08:30 - 09:00 can access the specific word in the memory. But actually, we also need a digital circuit, which will accept this address as an input. And based on that input, it will select the specific word in the memory. So here for that, we will require a decoder for the address decoding. So in this decoder, we will apply the k-bit address, and based on that address, it will select the specific word in the memory. So in the next video, we will talk more about this address decoding.
• 09:00 - 09:30 And with the help of the timing diagram, we will also understand how the read and write operations are performed in the RAM. But I hope in this video, you understood the basics of the random access memory. So if you have any questions or suggestions, then do let me know here in the comment section below. If you like this video, hit the like button and subscribe to the channel for more such videos.