Chapter 3 (Hardware)

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41 Terms

1
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abstraction
A method used to hide unneeded or complex details of a problem or idea

Found in lecture Chapter 3 - Hardware 1
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von Neumann Architecture
Computer architecture with four subsystems:1) Memory2) Input/Output Devices (I/O)3) ALU4) ControlTwo characteristics:1) Instructions are stored like data2) Instructions are executed sequentially

Found in lecture Chapter 3 - Hardware 2
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RAM
Random Access Memory.Memory is divided into cells. Each cell (aka minimum unit of access) is associated with an address. A standard cell width is 8 bits (1 byte). Must always access ENTIRE cell, even if you just want 1 bit.

Found in lecture Chapter 3 - Hardware 1 and zyBook Section 3.2
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ROM
Read Only Memory. ROM holds important system instructions and data such as the START UP instructions for a computer (aka firmware). Usually info has been prerecorded during manufacture.

Found in lecture Chapter 3 - Hardware 1
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volatile memory
Information disappears without power, e.g., RAM and cache (lose data on power loss)

Found in lecture Chapter 3 - Hardware 1 and zyBook Section 3.3
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non-volatile memory
Information preserved without power, e.g., ROM, disc, flash

Found in lecture Chapter 3 - Hardware 1 and zyBook Section 3.3
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cache
Stores DATA from a slower device to be accessed faster. On-chip memory used to decrease memory access times. Works because of locality.

- SMALL (on order of few megabytes) because it's expensive.
- FAST (5-10x faster than RAM)

We use cache to decrease memory access time.

Found in lecture Chapter 3 - Hardware 2 and zyBook Section 3.3
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cache hit
When requested data is found in cache

Found in lecture Chapter 3 - Hardware 2
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cache hit rate/ratio
Probability a data request will be a cache hit. In other words, the % of time that the info needed is in cache memory.

INCREASE cache hit ratio -> DECREASE overall memory access time.

- Good to know: Cache hit ratio CHANGES as system executes:
- Decreases as we move from one locality to another.
- Increases as we stay in the same locality (if cache is big enough to hold locality).

Found in lecture Chapter 3 - Hardware 2
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cache miss
When requested data is not found in cache

Found in lecture Chapter 3 - Hardware 2
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What can we do to increase cache hit ratio?
- Increase size of cache (can store more, small cache size can yield 75% hit ratio).

- Be smarter about what to put in the cache (Studies show 98% of process time is spent in localities. If OS can be smarter about what to put in cache -> increase hit ratio)

Found in lecture Chapter 3 - Hardware 2
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memory cell
Fixed sized unit of memory. Standard size = 8 bits = 1 byte
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address
Unique identifier for a memory cell.

Address space = MAX # of possible addresses.

Example question: Suppose RAM addresses are N bits. How many memory cells can theoretically exist?2^N.

If 16 bit ADDRESS, how many cells could exist in memory? 65,536 (64K).

Found in lecture Chapter 3 - Hardware 1
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register
Stores VALUES that are BEING USED during processing.

Special high speed storage cell that holds something specific. Note: registers are not designed for general purposes like other types of memory (e.g., cache, ram)

Found in lecture Chapter 3 - Hardware 3
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ALU
Arithmetic Logic Unit. Performs math and logical operations (e.g., addition, subtraction, comparisons, and, or, not)

Found in lecture Chapter 3 - Hardware 2 and zyBook Section 3.2
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control unit
Component of processor that FETCES, DECODES, and EXECUTES instructions.

Found in lecture Chapter 3 - Hardware 2 and zyBook Section 3.2
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processor
ALU + control unit

Found in lecture Chapter 3 - Hardware 2 and zyBook Section 3.2
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interrupt
An input signal to the processor indicating an event that needs immediate attention. Alerts the processor and serves as a request for the processor to interrupt the currently executing code, so that the event can be processed in a timely manner.

Found in lecture Chapter 3 - Hardware 3
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Moore's Law
Since the invention of the IC (integrated circuit) around 1960, IC's have doubled in circuit capacity about every 1.5 or 2 years.

Found in lecture Chapter 3 - Hardware 2 and zyBook Section 3.7
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truth table
One way to describe the behavior of a combinational circuit, listing the output value for every possible combination of input values.

Found in lecture Chapter 3 - Circuits 1 and zyBook Section 3.1
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transistor
a device with no mechanical/moving parts that can be OFF or ON

Found in lecture Chapter 3 - Circuits 2 and zyBook Section 3.7
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tautology
A Boolean expression that is always true. Example: (A OR B) OR (NOT A)

Found in lecture Chapter 3 - Circuits 1
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circuit
a collection of logic gates that transforms a set of binary inputs into a set of binary outputs.

Found in lecture Chapter 3 - Circuits 1 and zyBook Section 3.1
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gate
an electronic device with 1+ transistors that operates on a set of binary inputs to produce a binary output.

Found in lecture Chapter 3 - Circuits 1 and zyBook Section 3.1
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boolean expression
an expression that evaluates to either true or false

Found in lecture Chapter 3 - Circuits 1
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boolean logic
An area of mathematics dealing with rules for manipulating true and false

Found in lecture Chapter 3 - Circuits 1
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computer
a device that:
1) Takes input.
2) Processes the input in some way.
3) Produces output (a result).

Found in lecture Chapter 3 - Hardware 1
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von Neumann Bottleneck
- As CPU speeds have increased, CPU idle time has increased (due to waiting for data to be fetched from memory).

- Needs significant changes to computer architecture to handle larger problems.

Found in lecture Chapter 3 - Hardware 2
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Two key issues with von Neumann architectures and how we might solve them
TWO ISSUES:

1. Inability to place circuits closer together on a chip. Moore's Law is slowing down! Slow down in processor speed while our problems to be solve are getting larger!-> Solution: Parallel Processing (multi-processor). "If you can't build something to work twice as fast, build it to do two things at once. The results will be identical".

2. Slow speed to access memory.-> Solution: adding a cache helps. Adding multi-threading helps. Adding new types of RAM (e.g., DDR SDRAM) helps. But NONE solve the full problem. No matter how fast a given CPU can work, it is limited by the rate of memory transfer.

Found in lecture Chapter 3 - Hardware 2
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Memory vs. Disc
Discs are SLOW (order of magnitude slower than memory).

Solid state disc (SSD) are more common for discs now:
- no moving part -> faster
- more expensive $$$

Why not use SSD as RAM?
- SSD are starting to get as fast as RAM, but SSDs wear out (would wear out fast if accessed it OFTEN, like we do with RAM).
- SSDs optimized to act as a disc. RAM optimized to act as memory.

Found in lecture Chapter 3 - Hardware 2
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bootloader
Transfers OS from a pre-determined location into RAM. Jump to OS for system run.

Found in lecture Chapter 3 - Hardware 2
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The 4 basic instruction types
Data transfer: moves data to/from memory and I/O devices.

Arithmetic: Calculate numerical operations. (e.g., add)

Comparison: Compare 2 values (e.g., ==,
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instruction set
Set of all operations that can be executed by a processor. Set of all implemented opcodes.

Found in lecture Chapter 3 - Hardware 3
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address fields
Second part of machine instruction. Specifies which memory addresses are being operated on. (up to 3)

Found in lecture Chapter 3 - Hardware 3
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Operation code (opcode)
Opcode. First part of machine language instruction. Specifies which operation needs to be carried out (e.g., addition, store)

- If 2-bit OPCODE, how many different instructions are possible? Four (01 Input, 11 Add, 10 Output, 00 Stop).

- If 8 bit OPCODE? 2^N = 2^8 = 256 different instructions are possible.

Found in lecture Chapter 3 - Hardware 3
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machine language
Binary representation of program instructions. Each machine language instruction has 2 types of fields:
1. an opcode (specifies which operation needs to be carried out).
2. address fields (specifies what memory addresses are being operated on).

Found in lecture Chapter 3 - Hardware 3
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execute
Control unit action: Execute instruction by issuing appropriate command

Found in lecture Chapter 3 - Hardware 3
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decode
Control unit action: use OPCODE to determine what to do for an instruction.

Found in lecture Chapter 3 - Hardware 3
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fetch
Control unit action: fetch the next instruction from memory at address stored in PC (program counter).

Fetch gets value at an address (nondestructive fetch)
- Value remains in memory
- Load MAR, Decode MAR (fetch address; place in MDR)
- return value in MDR

Found in lecture Chapter 3 - Hardware 3
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MIPS
millions of instructions per second

Found in lecture Chapter 3 - Hardware 3
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GIPS
billions of instructions per second

Found in lecture Chapter 3 - Hardware 3