11 - CPU (Central Processing Unit)
What are the benefits of multi-core processors?
- High clock speeds leads to fast power consumption - With users wanting to multi-task, dual-core processors can process different tasks and a such neither is pushed to their limit, lowering power consumption
What is the GSM processor?
- Referred to as the BP processor due to its function as a baseband radio processor -It handles WiFi and Bluetooth links - Baseband data sent as a digital signal through a single channel using the full bandwidth of the media - Communication is bidirectional - it uses the same channel to send and receive signals
What is CPU speed?
- The CPU undertakes the instructions it receives from programs in a cycle - The speed of a CPU is measured i how many cycles it can perform in a second - 1 cycle per second = 1 hertz - 1 million cycles per second = 1 megahertz (MHz) - 1 billion cycles per second = 1 gigahertz (GHz) - More speed = more instructions per second - However, more speed = a hotter processor and more power
What is the CPU - Central Processing Unit?
- The brain of the computer - It processes the data and completes all the tasks the computer carries out - At the heart of the CPU is a processor - Some CPUs have more than 1 processor (dual core, quad core) - Each processor has its own cache and controller which means they can perform multiple tasks at the same time, but because they are linked they can perform functions much faster than a single processor
What is web browser cache?
- Web browsers store certain items that have been downloaded in a folder - The browser assumes you will want to view these again so holds them in the cache, using temporal locality - When you visit a webpage your browser checks the cache to save time downloading data again - A problem is that these folders can occupy large amounts of hard disk drive space, so you should empty the cache regularly
What is different in mobile CPUs power consumption?
Mobile processors are also optimised for a very low power consumption.
How many CPUs do mobile devices usually have?
Most mobile devices have at least 2 CPUs - 1 dedicated processor for GSM (Global System for Mobile Communications) - A general processor (potentially multi-core) for apps and user interface. This is know as the application processor or AP
What happens in the mobile processor?
Originally each processor had its own memory, peripherals, clock speed etc. The search for smaller and more compact systems has led to a single RAM and flash chip being decided by assigning portions of each between the 2 processors.
What is Cache Organisation?
Temporal locality - CPU accesses data and the cache knows it might be needed again, so stores it ready for this time Spatial locality - CPU accesses a particular location in memory and the cache knows it will also need data stored close to the original, so it fetches that as well Sequential locality - CPU accesses data and knows that it is likely to need data in location s + 1 so it fetches that as well
Why is a larger cache not always beneficial?
The larger the amount of cache the system has, the more likely it is to register a hit when it access the RAM. However, it is slower to access the data with a larger cache.
What is different in mobile CPUs size?
The physical size of the portable device means that there is not much space, so most modern mobile phone processors also have other components integrated into the processor itself. These components often include things like wireless networking.
What is cache?
There are different levels of cache - L1. Built into the CPU (Usually 8-64 KB) - L2. Originally external to the CPU, but integrated into many modern CPUs (Usually 512 KB, but can go as high as 1-2 MB) - L3. Extra cache built into the motherboards between the microprocessor and main memory
What is different in mobile CPUs clock speed?
There is a different processor clock speed. The cooling requirements of any portable device require a processor that does not create too much heat. Portable processors always have lower clock speeds than their desktop equivalent as this lowers the amount of heat they produce.
What is a cache miss?
When data is not found, and cache has to fetch it from the RAM
What is a cache hit?
When the Cpu finds the data required in the cache.
