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What is the first step when executing the LOAD X operation?
Which operation sends data in MDR to the ALU during the ADD X operation?
What is the purpose of the COMPARE X operation?
In the JUMPGT X operation, what condition must be met to jump to X?
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What happens to the Program Counter (PC) after the FETCH operation?
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What type of memory is primarily lost when power is turned off?
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Which of the following storage devices offers the fastest data access speed?
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What primarily influences the time it takes to retrieve data from a disk?
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How does the I/O Controller assist the processor with data transfer?
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Which of the following operations is NOT performed by the Arithmetic/Logic Unit (ALU)?
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What is the primary role of the decoder in the ALU?
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Which components are classified as Direct Access Storage Devices (DASDs)?
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Which of the following statements about RAM is correct?
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What are the four major subsystems of the Von Neumann architecture?
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Which component holds the memory address to be accessed during a data operation?
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What is the primary purpose of cache memory?
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How does the fetch operation differ from the store operation in terms of memory access?
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What does the principle of locality refer to in relation to cache memory?
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What role does the decoder play in the memory system circuits?
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What type of random access memory (RAM) is characterized by its inability to be modified?
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What is stored in the Memory Data Register (MDR) during the memory access process?
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In typical instruction sets, what is the significance of how instructions are encoded?
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What is the maximum memory size calculated as $2^N$ where $N$ is the length of an address?
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What is a fundamental problem associated with Von Neumann architectures?
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Which of the following is NOT a characteristic of MIMD parallel processing?
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What limits the miniaturization of computer chip components?
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Which of the following examples represents a type of parallel processing?
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What is a key feature of parallel algorithms in the context of contemporary computing?
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Which component in a Von Neumann machine manages the execution of programs stored in memory?
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What distinguishes quantum computing from traditional computing systems?
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Which of the following best describes the concept of the Von Neumann bottleneck?
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What is the primary purpose of the ALU in a computer system?
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In the fetch/decode/execute cycle, what does the decode phase primarily handle?
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Which component holds the address of the next instruction to be executed?
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How do the instruction sets of RISC and CISC architectures primarily differ?
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What role does the multiplexer play in the ALU operations?
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What is the function of the 'branch' instruction in programming?
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Which of the following components is responsible for executing instructions?
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How does the control unit communicate with other components?
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What characterizes a Reduced Instruction Set Computer (RISC)?
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What does the term 'stored program characteristic' refer to?
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Study Notes
Von Neumann Architecture
- The foundation for nearly all modern computers
- Has four subsystems: memory, input/output, arithmetic/logic unit (ALU), and the control unit.
- The ALU and control unit are often bundled inside the central processing unit (CPU)
Memory and Cache
- Memory: functional unit where data is stored and retrieved
- Random access memory (RAM) is organized into cells with unique addresses
- All cells can be accessed in the same amount of time
- Cell values can be read and changed
- Read-only memory (ROM) has prerecorded information that cannot be modified
- Cell size/memory width is typically 8 bits.
- Maximum memory size/address space is 2N, where N is the length of the address
- Fetch: retrieve from memory (nondestructive)
- Store: write to memory (destructive)
- Memory access time is the time required to fetch/store, modern RAM requires 5-10 nanoseconds
- Memory address register (MAR) holds memory address to access
- Memory data register (MDR) receives data from fetch and holds data to be stored
- Circuits: decoder and fetch/store controller
- Decoder converts MAR into a signal for a specific memory cell
- Fetch/Store controller routes data flow to/from memory cells and MDR
- RAM speeds have increased slower than CPUs
- Cache memory is fast due to its location in the CPU
- Principle of locality: Values near recently accessed memory locations are more likely to be accessed, so they are loaded into the cache
- Cache hit rate: percentage of times values are found in the cache
Input/Output & Mass Storage
- Input/output (I/O) connects a processor to the outside world
- I/O examples: keyboard, monitor, hard drive, DVD, flash drive, and other computers.
- RAM is volatile memory (disappears without power)
- Mass storage systems are nonvolatile memory
- Direct access storage devices (DASDs)
- Sequential access storage devices (SASDs)
Direct Access Storage Devices (DASDs)
- Examples: Hard drives and optical media (CDs/DVDs)
- Tracks: concentric rings around the disk surface
- Sectors: fixed-size segments of tracks, the unit of retrieval
- Time to retrieve data is based on: Seek time, Latency, and Transfer time
- Nondisk DASDs: flash memory and solid-state drives (random access mass storage)
Sequential Access Storage Devices (SASDs)
- Examples: Magnetic tapes
- Data is accessed sequentially, like a cassette tape
- Much slower than DASDs.
I/O Controller
- Manages data transfer with slow I/O devices, freeing the processor for other tasks.
- Sends an interrupt signal to the processor when an I/O task is done.
The Arithmetic/Logic Unit (ALU)
- Part of the processor
- Contains circuits for arithmetic: addition, subtraction, multiplication, and division
- Contains circuits for comparison and logic: equality, and, or, not
- Contains registers: high-speed, dedicated memory connected to circuits
- Data path: how information flows in the ALU: from registers to circuits and back to registers
- To choose the operation to perform, a multiplexer selects one output from multiple circuits.
- Information flow: Data comes from registers to ALU, the ALU sends a signal to the multiplexer which selects the output. This result is then sent back to the register and out to the system.
The Control Unit
- Stored program characteristic: programs are encoded in binary and stored in the computer's memory
- Fetches instructions from memory, decodes them, and executes them
- Instructions are encoded as an operation code (op code) and an address
- Op code tells which operation to perform
- Addresses tell which memory locations/registers to operate on
- Machine language: binary strings that encode instructions, instructions can be carried out by hardware, sequences of instructions encode algorithms
- Instruction set: instructions implemented by a particular chip, every processor has a different set.
- Reduced Instruction Set Computer (RISC): Small instruction set, each instruction is highly optimized, and easy to design hardware.
- Complex Instruction Set Computer (CISC): Large instruction set, single instruction can do a lot of work, but complex to design hardware
- Modern hardware is a compromise between RISC and CISC
- Instruction set examples: Data transfer, arithmetic, comparison, branch
- Branching: allows for conditional and loop forms (allows control to jump to a nonsequential instruction)
- Control Unit contains: Program counter (PC) register: holds address of next instruction, Instruction register (IR): holds encoding of current instruction, and Instruction decoder circuit: decodes op code and signals helper circuits. Helper circuits send addresses to proper circuits and signal ALU, I/O controller, and memory.
Fetch/Decode/Execute Cycle
- The Von Neumann machine repeats this cycle until a HALT instruction or error occurs.
- Fetch Phase: get the next instruction into memory.
- Decode Phase: instruction decoder gets the op code
- Execute Phase: each instruction behaves differently.
Putting the Pieces Together
- The Von Neumann architecture combines the preceding parts of the system.
Notation for computer's behavior
- CON(A): contents of memory cell A
- A→B: send value in register A to register B
- FETCH: initiate a memory fetch operation
- STORE: initiate a memory store operation
- ADD: Instruct the ALU to select the output of the adder circuit - SUBTRACT: Instruct the ALU to select the output of the subtract circuit
Execute Phase Examples
- LOAD X: CON(X) → R
- STORE X: R → CON(X)
- ADD X: R + CON(X) → R
- JUMP X: get next instruction from address X
- COMPARE X: if CON(X) > R then GT=1, else 0. if CON(X) = R then EQ=1, else 0. If CON(X) < R then LT=1, else 0
- JUMPGT X: if GT=1, then jump to X, else continue to next instruction
Non-Von Neumann Architectures
- Problems become larger, but CPU speed is no longer increasing exponentially
- Heat and speed of light limitations
- Von Neumann bottleneck: sequential machines have trouble handling large problems
- Non-Von Neumann architectures are experimental/theoretical, except parallel processing
- Parallel processing: multiple processing units operating at the same time, used in supercomputers, multicore desktop machines, “the cloud,” and quantum computing.
- MIMD (Multiple Instruction Stream/Multiple Data Streams) parallel processing is used in cluster computing.
- Cluster computing: multiple, independent processors. Each ALU operates on its own data. Processors operate independently with their own data, program, and rate.
Summary of the Von Neumann Architecture
- A standard for computers, it has memory, I/O, ALU, and control unit with programs stored in memory.
- Execution is sequential unless the program dictates otherwise
- Memory is organized into cells with addresses, data is fetched and stored based on MAR and MDR, and uses decoder and fetch/store controller
- Mass data storage (DASDs) is nonvolatile and consists of disks with sectors and tracks
- I/O is slow, needs a dedicated controller to free the CPU.
- ALU performs computations based on registers.
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Description
Explore the fundamentals of the Von Neumann architecture, which is the basis for modern computing systems. This quiz covers key concepts such as memory, cache, and the various subsystems including the control unit and arithmetic/logic unit (ALU). Test your understanding of how these components work together in computer systems.
