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Interactive Audio Lesson
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Basic Concept of Memory Expansion
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Today, we're discussing memory location expansion. Can anyone tell me what it might mean?
I think it means increasing the amount of memory available!
Exactly! By using more than one memory chip, we can expand the memory locations. For instance, by combining two 16Γ8 memory chips, we can create a 32Γ8 chip. Does anyone know how many address lines we would need for that?
Five address lines?
Correct! Now letβs look at how those address lines interact with the chips.
Selecting Components of Memory Chips
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When we look at the address inputs for our chips, four lines are common. We only need to differentiate with the most significant bit. Can someone explain how that works?
The MSB would help to select which chip is being used?
Correct! For address inputs from 00000 to 01111, RAM-1 is selected, and from 10000 to 11111, it's RAM-2. Why do you think this is useful?
It helps us manage memory more efficiently and makes more memory available without needing complex wiring.
Exactly! Efficient management is key in memory design.
Practical Example of Memory Configuration
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Letβs examine an example. If we use two 16MB RAM chips to create a total of 32MB, how are the address lines structured?
There would be 25 address lines since 32MB equals 2 to the power of 25?
Exactly! With the two RAMs, for the addresses from 0000000 to 0FFFFFF, RAM-1 is selected. Can anyone tell me what happens at 1000000?
That would select RAM-2!
Great job! This concept of active selection is crucial in expanding available memory.
Introduction & Overview
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Quick Overview
Standard
Memory location expansion is achieved by using multiple memory chips, such as 16Γ8 chips, to create larger memory configurations, demonstrated through various examples. The section details how address inputs are used to select corresponding chips based on the most significant bit (MSB).
Detailed
Memory Location Expansion
Memory location expansion refers to the technique of utilizing multiple memory chips to increase the number of available memory locations in digital systems. For example, using two 16Γ8 memory chips can expand the memory space to a 32Γ8 configuration, thereby necessitating five address lines to access these expanded locations.
In practical terms, four of the five address lines are shared between both chips, while the most significant bit (MSB) determines which chip is selected. The section elaborates that for address inputs ranging from 00000 to 01111, RAM-1 is active, and for the range from 10000 to 11111, RAM-2 becomes active.
The significance of memory location expansion lies in its capacity to effectively utilize hardware to enhance memory without overwhelming the system architecture, thereby optimizing performance and functionality in electronic designs.
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Using Multiple Memory Chips
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Figure 15.23 shows how more than one memory chip can be used to expand the number of memory locations. Let us consider the use of two 16Γ8 chips to get a 32Γ8 chip. A 32Γ8 chip would need five address input lines. Four of the five address inputs, other than the MSB address bit, are common to both 16Γ8 chips. The MSB bit feeds the input of one chip directly and the input of the other chip after inversion. The inputs to the two chips are common.
Detailed Explanation
In this section, we learn how to increase the number of memory locations in a system by utilizing multiple memory chips. If we have two memory chips with a capacity of 16Γ8 (where 16 is the number of memory locations, and 8 is the number of bits per location), we can wire them together to create a larger memory space, like a 32Γ8 memory chip. However, to do this, we need to carefully manage the address inputs. The higher-order bit (MSB) will control which chip is being accessed directly, while the other bits act as common inputs for both chips to ensure they respond to the same memory location commands.
Examples & Analogies
Think of two separate filing cabinets (the memory chips), each with 16 drawers (memory locations). To create a single system with 32 drawers, we keep the same handle for the first set of 16 drawers (the common address inputs) but add a unique lock on the first cabinet (the MSB) that decides whether to open the first cabinet or the second one. If you want to access a drawer in the first cabinet, the lock needs to be in a certain position (MSB = 0); for the second cabinet, the lock position changes (MSB = 1).
Memory Location Selection
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Now, for the first half of the memory locations corresponding to address inputs 00000 to 01111 (a total of 16 locations), the MSB bit of the address is β0β, with the result that RAM-1 is selected and RAM-2 is deselected. For the remaining address inputs of 10000 to 11111 (again, a total of 16 locations), RAM-1 is deselected while RAM-2 is selected. Thus, the overall arrangement offers a total of 32 locations, 16 provided by RAM-1 and 16 provided by RAM-2. The overall capacity is thus 32Γ8.
Detailed Explanation
This chunk explains how the memory locations are mapped to specific RAM chips based on the address inputs. For the first 16 addresses (from 00000 to 01111), the MSB is 0, which means only the first chip, RAM-1, is active (or selected). Conversely, for the last 16 addresses (from 10000 to 11111), the MSB is 1, so now only the second chip, RAM-2, is selected. This selective activation allows us to effectively use two chips to create a seamless 32-location memory space, with each chip contributing half of the total capacity.
Examples & Analogies
Imagine you have a two-story library (the memory chips), where the first floor has a total of 16 bookshelves (locations) and the second floor has another 16. When you are asked for book titles that start with A to M, you look on the first floor (MSB = 0). But when you are given titles that start with N to Z, you now head to the second floor (MSB = 1). This ensures you never have to look in both places at the same time.
Definitions & Key Concepts
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Key Concepts
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Memory Expansion: The practice of combining multiple chips to increase memory capacity.
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Address Line Functionality: Mechanism by which chips are selected based on input addresses.
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MSB's Role: Its critical function in determining which memory chip is active.
Examples & Real-Life Applications
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Examples
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Using two 16Γ8 memory chips to create a 32Γ8 memory configuration.
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Two 16MB memory chips combined to form a 32MB arrangement.
Memory Aids
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π΅ Rhymes Time
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In memory chips we stack, one on the other, / For larger memory, together they cover.
π Fascinating Stories
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Once there were two memory chips, feeling small. But together they built a tower, standing tall, expanding memory and making use of their all!
π§ Other Memory Gems
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MESA - Memory Expansion: Select Address lines (MSB) Active.
π― Super Acronyms
RAM - Readily Accessible Memory; we expand it in layers.
Flash Cards
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Glossary of Terms
Review the Definitions for terms.
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Term: Memory Location Expansion
Definition:
A technique used to increase the number of available memory locations in a digital system by combining multiple memory chips.
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Term: Address Input
Definition:
The wiring inputs used for selecting specific memory locations within a chip.
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Term: Most Significant Bit (MSB)
Definition:
The highest order bit in a binary number, used to determine the selection of memory chips.