Address Representation
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Introduction to Program Execution
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Today, we're going to discuss the execution of a program in a processor. Can anyone tell me what a program consists of?
It consists of a set of instructions?
Exactly! Each instruction is executed in sequence. The processor fetches an instruction from memory and then executes it. This process is called the instruction cycle. Remember, 'fetch and execute' — that's a key concept to keep in mind!
So what happens during the fetch phase?
Great question! During the fetch phase, the Program Counter provides the address of the next instruction, which is loaded into the Instruction Register. This is crucial for the execution process.
What if there are multiple instructions?
If there are multiple instructions, the CPU will continue to fetch each instruction until the program ends. This is part of a cycle that repeats. Are you all with me?
Yes, it's a loop of fetching and executing instructions!
Exactly! Remember it like this: 'Fetch, then execute, repeat!'
So to summarize, a program consists of a series of instructions, and the CPU uses the fetch-execute cycle to carry them out.
Instruction Formats
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Next, let’s talk about instruction formats. What do you think an instruction format includes?
Doesn’t it include the opcode and address?
Exactly! Each instruction typically consists of an opcode, which specifies the operation to be performed, and the address of the operand. The machine code is usually structured in binary, which represents both parts.
How do these parts help in executing instructions?
Good question! The opcode tells the CPU what action to take, while the address tells it where to find the necessary data or where to send results. Remember: 'Opcode is the action, Address is the location!' understand?
What happens if the address isn't found?
If an instruction tries to access a nonexistent memory address, it can cause an error called a segmentation fault. That's why understanding how addresses work is crucial.
To summarize, an instruction format consists of an opcode and an address, critical for executing the correct operation.
Program Counter and Registers
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Now, let's go deeper into some components, starting with the Program Counter. Can anyone explain its purpose?
It keeps track of the address of the next instruction.
Correct! The Program Counter is crucial for sequential instruction execution. When an instruction is fetched, the PC is updated to point to the next instruction. What are some other important registers in the CPU?
Instruction Register and Accumulator?
That's right! The Instruction Register holds the current instruction, while the Accumulator temporarily stores results. Remember the acronym 'PIA'—Program Counter, Instruction Register, and Accumulator.
So why are these registers important?
These registers optimize data handling and contribute to efficient execution. In summary, the Program Counter, Instruction Register, and Accumulator form the backbone of instruction execution.
Memory Size and Address Calculation
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Let's discuss memory sizes and how they relate to addresses. How do we determine the maximum memory the processor can address?
Is it based on the size of the address bus?
Exactly! For example, a 12-bit address bus can access 2^12 or 4096 memory locations. Each location can hold a specific number of bits.
What if each memory location holds 16 bits?
In that case, with 4096 (4K) locations, you can represent a total of 4K * 16 bits of data. It's essential for understanding how much information can be stored.
Does this impact instruction execution speed?
Definitely! More memory can reduce access time and provide more data for processing. Summarizing, the address bus size directly affects the accessible memory spaces, influencing the data handling capacity of a CPU.
Introduction & Overview
Read summaries of the section's main ideas at different levels of detail.
Quick Overview
Standard
In this section, the topics of program execution in processors, instruction formats, and the various levels of programming languages are explored. Key components of a computer's architecture, including memory sizes and registers, are defined alongside a detailed example illustrating instruction execution.
Detailed
Address Representation
This section provides a comprehensive overview of how addresses are represented in computer architecture and the associated processes during program execution. It begins by highlighting the objectives outlined for understanding program execution within a processor and delves into the essential components comprising computer architecture, including the Central Processing Unit (CPU), Main Memory, and Input/Output devices.
The section explains that the CPU performs operations based on a series of instructions stored in memory, adopting the von Neumann architecture principle of storing both program instructions and data. An essential focus is placed on the instruction cycle, which consists of fetching and executing instructions. The discussion also includes a breakdown of a sample program execution, demonstrating how hexadecimal memory addresses correlate to binary representations and analyzing fetch and execution cycles.
Key registers, such as the Program Counter (PC), Instruction Register (IR), and Accumulator (AC), are described, emphasizing their roles in managing memory addresses and data flow. The various instruction formats are highlighted alongside their opcodes, illustrating how operations such as loading, storing, and adding are handled in processors designed around accumulator architecture.
Furthermore, the section explores the potential of a 12-bit address bus to access 4096 memory locations with 16 bits of data per location, elucidating both the theoretical and practical implications of these concepts as students delve into specific instruction examples, depicting how high-level programming constructs translate into low-level operations within a CPU.
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Address Size and Binary Representation
Chapter 1 of 4
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Chapter Content
So, this 12 bits basically if I am having an address bus of size 12 bit. Then what is the maximum Memory that we can address over here? This is your 2^12. So that means, 4K Memory location we are having. So, 2^2 = 4 and 2^10 is your K. So, total we are having 4K Memory location.
Detailed Explanation
In this chunk, we learn about the address size of a memory unit and how we derive the maximum addressable memory from it. The address bus consists of 12 bits, which means we can represent numbers from 0 to 2^12 (or 0 to 4096). Thus, we can access 4K memory locations because there are 4096 individual addresses available to us in this scenario.
Examples & Analogies
Think of the address bus as a street that houses a certain number of mailboxes (memory locations). If your street has 12 houses (the 12 bits), you can number them from 0 to 4095, giving you a total of 4096 mailboxes (or 4K mailboxes) where you can store letters (data).
Memory Location and Data Size
Chapter 2 of 4
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Chapter Content
And what is the size of this particular Memory location? How many bits we can store inside this particular Memory location? You just see one of the content is your 1940. So, this is in hexadecimal. What is the binary representation 0001100101000000. So, this is the information that we have in the Memory location 300 in hexadecimal.
Detailed Explanation
This chunk discusses how data is stored within a memory location, specifically focusing on a memory content example. In this case, the content 1940 is presented in hexadecimal format, which can be converted into binary as 0001100101000000. This shows that each memory location can hold 16 bits or 2 bytes of information.
Examples & Analogies
Imagine each mailbox from our previous example can hold a specific number of letters. If each mailbox holds exactly 2 letters (or 16 bits of data), then every memory location (or mailbox) serves as a clasp that securely stores data, just like letters in a mailbox.
Instruction Breakdown and Execution Phases
Chapter 3 of 4
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Chapter Content
So, if you see that we are having the Instruction in Memory location 300, 301, and 302; that means, we must start our execution from the Memory location 300. So, in that particular case in 300 this 300 address of the Memory location we are storing in this particular program counter. Now program counters know which Instruction we need to Fetch or from which Memory location we need to fetch.
Detailed Explanation
In this section, we examine how the instruction cycle begins. We start instruction execution from a specified memory location, like 300. The program counter keeps track of what instruction to fetch next from memory. The process involves fetching the instruction from the current address, executing it, and then updating the program counter to the next address to continue program execution.
Examples & Analogies
Consider the program counter as a librarian who always remembers the page number of the book currently being read. When the librarian reads a page (fetches the instruction), they write down the next page number to read next (updating the program counter). This ensures the reading continues smoothly without losing track of where to go next.
Understanding Instruction Format
Chapter 4 of 4
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Chapter Content
So here we are having total 16 bits. Basically it is your 2 bytes; that means, in every Memory location we can store 2 bytes of information. Now what does this Instruction mean 1940? Now we have to see because by just looking into it we cannot understand anything, but if we are going to interpret it properly then we are going to get some meaningful information.
Detailed Explanation
This chunk highlights the instruction format. Each instruction consists of 16 bits, divided into two parts: the operation code and the address of the operand. For example, the instruction '1940' can be broken down to identify what action to take and where to find the necessary data. Understanding this format is essential for making sense of the instructions sent to the processor.
Examples & Analogies
Imagine a recipe card containing two key pieces of information: what dish to cook (operation) and where to find the ingredients (address). To prepare a meal (execute the instruction), you need both parts to create the dish in the correct manner.
Key Concepts
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Program Execution: The process by which a CPU fetches and executes instructions in a program.
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Instruction Cycle: The cycle composed of fetching and executing instructions.
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Opcode and Address: The two main components of an instruction that determine the operation and where to access data.
Examples & Applications
Executing a simple program involves the CPU fetching instructions from memory using the Program Counter.
A 12-bit address bus allows accessing 4096 memory locations, impacting how instructions are executed.
Memory Aids
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Rhymes
Fetch for the next instruction to see, Execute it next, that's the key!
Stories
Imagine a librarian (CPU) who fetches the next book (instruction) to read (execute) and keeps track of which one comes next with a small bookmark (PC).
Memory Tools
F.E.E. - Fetch, Execute, and Execute again!
Acronyms
IRA - Instruction, Registers, Address for quick recall.
Flash Cards
Glossary
- Program Counter (PC)
A register in the CPU that holds the address of the next instruction to execute.
- Instruction Register (IR)
Register that holds the currently fetched instruction.
- Accumulator (AC)
A register used to store intermediate results of arithmetic and logic operations during instruction execution.
- Opcode
The part of an instruction that specifies the operation to be performed.
- Address Bus
A system within the computer that carries memory addresses from the CPU to other components.
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