Chp. 2 - C: Processors & Memory

What is a CISC?

- A CISC (complex instruction set computer) is refers to complex instruction sets that require several clocking cycles for execution - Most modern desktop and laptop computers uses CISC

What is a *cycle* when referring to microprocessors and clock speeds?

- A cycle is the smallest unit of time in a microprocessor's universe. Actions that the microprocessor performs are measured in cycles. Customary to equate clock cycles with number of instructions a processor can execute per second.

What is RISC?

- A microprocessor with a limited set of simple instructions uses RISC (reduced instruction set computer) - This performs most instructions faster than CISC, but may need more simple instructions to complete a task than a CISC processor requires for the same task. - Most processors in handheld devices use ARM (advanced RISC Machine) tech.

What is a *control unit* within a processor?

- A microprocessors control unit fetches each instruction, in the same way you might get ingredients for cookies out of a cupboard. Data is loaded into the ALU's registers, just like adding ingredients to the mixing bowl. Then the control unit gives the green light to begin processing, not unlike flipping a switch on a blender to mix ingredients

What does GHz have to do with processor performance / What is a microprocessor clock?

- A processor specification like 3.4 GHz, indicates the speed of the microprocessor clock - timing device that sets the pace for executing instructions. Most set in GHz (billion cycles per second).

Describe the booting process of a digital device

- A) Power on a device and wait for the boot loader program in ROM (which doesnt need power to hold data unlike RAM). Check hardware, verify software, load the OS B) RAM holds the OS C) OS boots

What is the ALU?

- ALU (arithmetic logic unit) is part of the microprocessor that performs arithmetic operations, like addition & subtraction. Also does logical operations (e.g. comparing 2 numbers). The ALU uses registers to hold data that is being processed

What is *Parallel Processing*?

- Executes more than one instruction at a time. Possible with multi-core processors. E.g. think multiple ovens that hold multiple pizzas

What is virtual memory?

- If a program exceeds its allocated space, the operating system uses an area of the hard disk or other storage medium as virtual memory to store parts of programs or data files until they are needed. Too much dependence on this can decrease performance (especially on a slow mechanical device, such as a hard disk drive).

What happens when a computer executes an instruction? What is an *instruction cycle*?

- Instruction Cycle refers to when a computer executes a single instruction. e.g. 1) Fetch an instruction, 2) Interpret the instruction, 3) Execute the instruction, 4) Go to the next instruction

Would a computer with a 2.13 GHz processor perform slower than a 3.4 GHz processor>

- Not necessarily; clock speed comparisons only valid when comparing processors within the same chip family. There are other factors to consider when comparing diff. chip families

What is *Serial Processing* ?

- Some processors execute instructions "serially" - one instruction at a time. The processor must complete all steps in the instruction cycle before it begins to execute the next instruction. Analogy: Pizza baking one a time in an oven (the microprocessor)

What is a multi-core processor? What is a "core" of a processor?

- The "core" of a processor is referring to the control unit and ALU. - A microprocessor that contains circuitry for more than one processing unit is a *multi-core processor* -> more cores usually equates to faster performance. E.g. The 2.4 GHz Intel i5 processor has 2 cores, giving it the equivalent of 4.8 GHz performance(2.4 x 2).

What is the *boot-loader* in ROM?

- The boot-loader in ROM tell a device how to start. Performs self-tests to find out if hardware is operating properly and may also verify that essential programs have not been corrupted. It then loads the OS into RAM.

What role does the control unit play in the microprocessor? Think of the instruction pointer.

- The machine language instructions for a particular program are held in memory. When the program begins, the memory address of the first instruction is placed in part of the microprocessor's *control unit* called the *instruction pointer.* - A) The control unit can go to the memory address, B) fetch the instruction by copying data from that address into its instruction register, C) Next, the control unit interprets the instruction and executes it

When does the ALU swing into action?

- When the ALU gets the go-ahead from the control unit, it A) processes the data and places the result in an accumulator, B) From the accumulator, the data can be sent to memory or used for further processing. C) When the computer completes an instruction,, the control unit increments the instruction pointer to the memory address of the next instruction, and the instruction cycle begins again

Why do digital devices has ROM?

- When you switch on a digital device, there is a waiting period while the device gets ready for use. While you wait, the ROM is performing its role to "boot" the device (in general it begins when you press the power button and ends when the device is ready to use). - ROM contains small set of instructions and data called *boot loader* (tell device how to start).

What impact does *word size* have on performance?

- Word size controls the amount of memory that the processor can access. E.g. Processors with a 32-bit word size can access a max 4GB of memory, whereas processors with a 64gb word size can potentially access terabytes. - A large word size gives processors the ability to handle more data during each processing cycle- leads to increased performance.

What is *word size*?

- Word size refers to the number of bits that a microprocessor can manipulate at one time. It corresponds to the size of the registers used by the control unit and the ALU. A processor with 64 bit word size, for example, has registers that can process 64 bits at a time.

Can I change the contents of ROM?

- changing the contents of ROM is called "flashing" - A) Repair: Contents of ROM can become corrupted due to surges etc. Flashing the ROM to restore the boot loader instructions could correct the problem - B) User Mods: Can flash the ROM with a modded boot loader to bypass programs that can be run on device. Called "jailbreaking" on iOS devices. - C) Updates: Manufactures provide updates to boot loader to patch security weaknesses.

What happens inside a computer chip?

A microprocessor contains miles of microscopic circuitry & millions of mini components divided into different kinds of operational units, like the ALU & control unit.

What is a *register*? (**Hint - it's part of the ALU)

A register lives within the ALU -> it holds data that is being processed. - Analogy: Think of it as a mixing bowl you might use to hold ingredients for cookies

The instruction cycle

A) The control unit can go to the memory address, B) fetch the instruction by copying data from that address into its instruction register, C) Next, the control unit interprets the instruction and executes it D) When the ALU gets the go-ahead from the control unit, it processes the data and places the result in an accumulator, E) From the accumulator, the data can be sent to memory or used for further processing. F) When the computer completes an instruction, the control unit increments the instruction pointer to the memory address of the next instruction, and G) the instruction cycle begins again

What is in an instruction set?

An instruction set contains a collection of instructions for actions that the circuitry in a microprocessor can perform -> E.G. ARM has 35 instructions, x86 has 100. Each instruction carries out a small task, like moving a number from computer memory into the processor or comparing two numbers. When these instructions are executed millions at a time, you achieve higher functionality.

What is a microprocessor?

An integrated circuit that contains all the functions of a central processing unit (CPU) of a computer. x86 refers to standard processor in desktops and laptops. Processors in modern desktops & laptops are x86 compatible, such as Intel i3, i5, i7 microprocessors.

What are machine language instructions like?

Baby steps -> E.g. ADD = 0000 0000 , Input = 0110 0011 , Multiply = 1111 0110

How Does RAM work?

In RAM, microscopic electronic parts called capacitors hold the bits that represent data. A charged capacitor is "turned on" and represents a "1". while a discharged capacitor represents a "0" bit. A RAM address on each bank helps the computer locate data, as needed, for processing.

RAM (Random Access Memory)

Memory modules on the motherboard containing microchips used to temporarily hold data, application program instructions, and the operating system while the CPU processes them. Information in RAM is lost when the PC is turned off.

What is the significance of microprocessor instruction sets?

Microprocessors are hard-wired to perform a limited set of activities, called *instruction sets*. These instruction sets are unique to processor families E.G. x86 processors use a different instruction set than ARM processors -> One reason why a game designed to run on a smartphone with ARM cannot directly run on your laptop with its Intel i7 processor

Which Processors are popular for tablets & smartphones?

Processors based on ARM tech. are for tablet computers & smartphones. Originally designed by ARM Holdings - they are energy efficient (characteristic for battery powered devices). Found in Apple iPads & iPhones, Microsoft Surface Tablet, etc. EG. Apple. A10, Cortex

What's the difference between programming language & machine language?

Programming languages (JS, Python, etc). are statements for programmers. Microprocessors cannot directly understand these programming languages, so the programs get converted/translated into *Machine Language* that corresponds to the microprocessors instruction set. These machine language instructions are binary strings of 0s & 1s that can be processed by a digital device.

Why is RAM important?

RAM is the "waiting room" for the microprocessor. It holds raw data waiting to be processed as well as the program instructions for processing the data. It also holds the results of the processing until they can be moved to a more permanent location such as an internal drive, cloud storage, etc. In addition, it also hold the OS instructions that control the basic functions of a computer system.

What is CPU cache?

Special high-speed memory that allows a microprocessor to access data more rapidly than from memory located elsewhere on the system board. Large cache can increase processing performance. - usually measured in megabytes - L1 (Level 1) cache is the fastest, L2 and L3 slightly slower but still faster than accessing main memory or disk storage

What is ROM?

Stands for Read-Only-Memory. 'read only' means that the content cannot be edited or deleted. It stores data or instructions which do not need to be changed. Housed on a single integrated circuit on the system board. More permanent and non-volatile. Contents of ROM remain in place even when the device is turned off.

What is *Pipeline Processing*?

When a processor begins to execute an instruction before it completes the previous instruction, it is using *pipeline processing*. - Analogy: Pizzas on conveyor belt within the oven. A pizza (instruction) starts moving along belt, and before its done, another pizza moves on the belt