Intro to comp sci chapter 5

What is Von Neumann architecture?

Foundation for modern computers

What are the four major subsystems of Von Neumann architecture?

Memory, Input/output, ALU, Control Unit

Where are the ALU and control unit often bundled?

Inside the CPU

What is memory?

Functional unit for storing/retrieving data.

What is Random Access Memory (RAM)?

Memory organized into cells with unique addresses.

What is Read-only Memory (ROM)?

Type of RAM with pre-recorded information that cannot be modified.

What is the cell size/memory width in memory?

Typically 8 bits.

What is the maximum memory size/address space?

2N, where N is the length of the address.

What is fetch?

Retrieve from memory (nondestructive fetch).

What is store?

Write to memory (destructive store).

What is memory access time?

Time required to fetch/store.

How long does modern RAM require for memory access time?

5-10 nanoseconds.

What does the Memory Address Register (MAR) do?

Holds memory address to access.

What does the Memory Data Register (MDR) do?

Receives data from fetch and holds data to be stored.

What are memory system circuits?

Decoder and fetch/store controller.

What is the function of a decoder?

Converts MAR into signal for a specific memory cell.

What is the difference between one-dimensional and two-dimensional memory organization?

One-dimensional is linear, while two-dimensional is grid-like.

What is the role of a fetch/store controller?

Acts as a traffic cop for MDR, routing data flow to/from memory cells and MDR.

What signal does the fetch/store controller take in?

A signal indicating fetch or store.

What is the relationship between RAM speeds and CPU speeds?

RAM speeds increased more slowly than CPU speeds.

What is cache memory?

Fast but expensive memory built into the CPU for fast access times.

What is the principle of locality?

Values close to recently accessed memory are more likely to be accessed. Load neighbors into cache and keep recent values there.

What is cache hit rate?

Percentage of times values are found in cache.

What is the purpose of Input/output (I/O)?

Connects the processor to the outside world

What are some examples of I/O devices for humans?

Keyboard, monitor, etc.

What are some examples of I/O devices for data storage?

Hard drive, DVD, flash drive

What are some examples of I/O devices for other computers?

Network

What is the function of RAM?

Volatile memory, lost without power

What are mass storage systems?

Nonvolatile memory

What are examples of direct access storage devices (DASDs)?

Hard drive, flash drive

What are examples of sequential access storage devices (SASDs)?

Tape drives, magnetic tape

What are DASDs?

Direct Access Storage Devices

What are the components of disks?

Tracks and sectors

What factors affect the time to retrieve data from disks?

Seek time, latency, and transfer time

What are examples of other nondisk DASDs?

Flash memory and solid-state drives

What are DASDs and SASDs?

Direct Access Storage Devices and Serial Attached SCSI Devices

How do DASDs and SASDs compare to RAM in terms of speed?

They are orders of magnitude slower than RAM, measured in microseconds or milliseconds.

What is the role of an I/O Controller?

To manage data transfer with slow I/O devices, allowing the processor to perform other tasks.

What happens when an I/O task is completed?

The controller sends an interrupt signal to the processor.

What is ALU?

Arithmetic Logic Unit, part of the processor.

What functions does ALU perform?

Arithmetic operations (addition, subtraction, multiplication, division), comparison, and logic operations (equality, and, or, not).

What are registers in ALU?

High-speed, dedicated memory connected to circuits.

What is data path in ALU?

The path through which information flows from registers to circuits and back to registers.

How is the operation to perform chosen?

Option 1: decoder signals one circuit to run.

How is the operation to perform chosen?

Option 2: run all circuits, multiplexer selects one output from all circuits.

Which option is usually chosen in practice?

Option 2 is usually chosen.

What is information flow?

Data movement between registers, ALU, and multiplexer.

What is the role of registers in information flow?

Registers receive data from outside.

What is the role of ALU in information flow?

ALU receives signals from registers.

What is the role of multiplexer in information flow?

Multiplexer selects and keeps a value, discarding the rest.

What happens to the result from the multiplexer in information flow?

The result goes back to the register and then to outside.

What is the stored program characteristic?

Programs are encoded in binary and stored in computer's memory.

What does the control unit do?

Fetches instructions from memory, decodes them, and executes them.

How are instructions encoded?

With an operation code (op code) and addresses for memory addresses/registers.

What is machine language?

Binary strings encoding instructions that can be executed by hardware.

What is an instruction set?

Instructions implemented by a specific chip or processor.

How do sequences of instructions encode algorithms?

By representing a series of steps to be executed by the hardware.

What is a Reduced Instruction Set Computer (RISC)?

Small instruction sets, highly optimized, easy hardware design.

What is a Complex Instruction Set Computer (CISC)?

Large instruction set, single instruction does a lot of work, complex hardware design.

What is the compromise between RISC and CISC in modern hardware?

A balance between simplicity and complexity in instruction sets and hardware design.

What is an instruction set?

A set of commands that a computer's processor can execute.

Give an example of a data transfer instruction.

Move data from memory to register.

What are arithmetic instructions used for?

Performing mathematical operations like addition and logical operations like AND.

What is the purpose of comparison instructions?

To compare two values.

What is branching in the context of instruction sets?

Changing to a nonsequential instruction.

What are the benefits of branching?

Enabling conditional and loop forms of execution.

Give an example of a branching instruction.

JUMPLT a = If previous comparison of A and B found A < B, then jump to instruction at address a.

What is an instruction set?

A set of commands that a computer's processor can execute.

Give an example of a data transfer instruction.

Move data from memory to register.

What are arithmetic instructions used for?

Performing mathematical operations like addition and logical operations like AND.

What is the purpose of comparison instructions?

To compare two values.

What is branching in the context of instruction sets?

Changing to a nonsequential instruction.

What are the benefits of branching?

Enabling conditional and loop forms of execution.

Give an example of a branching instruction.

JUMPLT a = If previous comparison of A and B found A < B, then jump to instruction at address a.

What is a Von Neumann machine?

A computer architecture that combines previous pieces.

What is the fetch/decode/execute phase?

A repeating cycle in a Von Neumann machine until HALT or error.

What is the fetch phase?

Getting the next instruction into memory.

What is the decode phase?

The instruction decoder retrieves the op code.

What is the execute phase?

The phase that varies for each instruction.

What happens in the fetch phase?

1. PC → MAR: Send address in PC to MAR

2. FETCH: Initiate fetch, data to MDR

3. MDR → IR: Move instruction in MDR to IR

4. PC + 1 → PC: Add one to PC

What happens in the decode phase?

1. IRop → instruction decoder

What happens in the execution phase?

Loading and storing data

What does LOAD X mean?

Copy data from CON(X) to R

What does STORE X mean?

Copy data from R to CON(X)

What happens in step 1 of the execution phase?

Send address X to MAR

What happens in step 2 of the execution phase?

Initiate fetch or send data to MDR

What happens in step 3 of the execution phase?

Copy data in MDR to R or initiate store of MDR to X

What does ADD X mean?

Perform addition operation using data in R and X, store result in R

What does IRaddr → MAR mean?

Send the address X to the Memory Address Register (MAR)

What happens during FETCH?

Initiate the fetch operation and transfer data to the Memory Data Register (MDR)

What does MDR → ALU mean?

Send the data in MDR to the Arithmetic Logic Unit (ALU)

What does R → ALU mean?

Send the data in R to the Arithmetic Logic Unit (ALU)

What does ADD circuit do?

Select the ADD circuit as the result of the operation

What does ALU → R mean?

Copy the selected result from the ALU to R

What does JUMP X mean?

Get the next instruction from address X

What does IRaddr → PC mean?

Send the address X to the Program Counter (PC)

What is the meaning of COMPARE X?

Comparison of X with R

What happens if CON(X) is greater than R?

GT is set to 1, else 0

What happens if CON(X) is equal to R?

EQ is set to 1, else 0

What happens if CON(X) is less than R?

LT is set to 1, else 0