Memory

• RAM is high speed volatile memory
• Random Access Memory (RAM) is used as the main memory in a computer. It can be read and written to
• RAM is volatile
• Volatile memory is temporary memory. It requires power to retain its data
• Non-volatile memory is permanent memory - it keeps its contents even when there is no power
• The main memory is where all data, files and programs are stored while they're being used
• When a computer boots up, the OS (operating system) is copied from secondary storage to RAM
• When software applications, documents and files are opened, they are copied from secondary storage to RAM. They stay in RAM until the files or applications are closed
• RAM is slower than the CPU cache, but way faster thaan secondary storage
• Never mix up memory and secondary storage - if a computer has a 2 TB hard drive, that doesn't mean it has 2 TB of memory
• Virtual memory is secondary storage used as extra RAM
• Computers have a limited amount of RAM
• As applications are opened, RAM fills with data
• When RAM is full, the computer needs somewhere else to put application data. It moves data that hasn't been used recently to a location on secondary storage known as virtual memory
• Virtual memory may be needed if there are too many applications open at once, or if a particularly memory-intensive application is being used (or both)
• If the CPU needs to read data stored in virtual memory, it must move the data back to RAM. This is slow as data transfer rates are much slower on secondary storage than RAM
• Using virtual memory can make a computer slow to respond when switching between applications (while data for one application in virtual memory is swapped with the other) or using a memory-intensive application
• ROM tells the CPU how to boot up
• ROM = Read Only Memory
• ROM is non-volatile memory
• ROM can only be read, not written to
• ROM comes on a small, factory-made chip built into the motherboard
• ROM contains all the instructions a computer needs to properly boot up. These instructions are called the BIOS
• BIOS = Basic Input Output System
• As soon as the computer is powered on, the CPU reads the instructions from ROM. This tells the CPU to perform self-checks and set up the computer
• Although the CPU can only read ROM, it is possible to update ('flash') the BIOS on the ROM chip
• The BIOS is a type of firmware - hardware-specific software built in to a device
• Embedded systems are controlled by firmware