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C OMPUTER H ARDWARE(3). What is RAM?. RAM (random access memory) is a temporary holding area for data, application program instructions, and the operating system.
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What is RAM? • RAM (random access memory) is a temporary holding area for data, application program instructions, and the operating system. • In a personal computer, RAM is usually several chips or small circuit boards that plug into the system board within the computer’s system unit.
Why is RAM so important? • RAMisthe“waitingroom”forthecomputer’sprocessor. • It holds raw data waiting to be processed as well as the program instructions for processing that data. • It holds the results of processing until they can be stored more permanently on disk or tape. • It also holds operating system instructions, that loaded when starting a computer, to control it’s basic functions.
How does RAM differ from hard-disk storage? • To differentiate between RAM and hard-disk storage: • RAM holds data in circuitry that’s directly connected to the system board, whereas hard-disk storage places data on magnetic media. • RAM is temporary storage; hard-disk storage is more permanent. • RAM usually has less storage capacity than hard-disk storage.
How does RAM work? • InRAM,microscopicelectronicpartscalledcapacitors hold the bits that represent data. • Can visualize the capacitors as microscopic lights that can be turned on or off. • Turned on capacitor represents a “1” bit and turned offcapacitor represents a “0” bit. • Each bankof capacitors holds eight bits—one byte of data.
How does RAM work? • A RAM address on each bankhelps the computer locate data, as needed, for processing. • Unlike disk storage, RAM is volatile: • Which means it requires electrical power to hold data. • If the computer is turned off or the power goes out, all data stored in RAM instantly and permanently disappears.
How much RAM does a computer need? • RAM capacity is expressed in megabytes or gigabytes. • Today’s personal computers typically feature 2–8 GB of RAM. • Amount of RAM a computer needs depends on the used software you. • RAM requirements are routinely specified on the outside of a software package.
How much RAM does a computer need? • Today’s computer operating systems are quite smart at allocating RAM space to multiple programs. • Ifaprogramexceedsitsallocatedspace,theoperatingsystem uses an area of the hard disk, called virtual memory,to store parts of programs or data files until they are needed.
Do all computers use same type of RAM? • RAM speed is often expressed in nanoseconds (ns) or megahertz (MHz millions of cycles per second). • Lower nanosecond ratings are better because it means the RAM circuitry can react faster to update the data it holds. • SDRAM (synchronous dynamic RAM) is fast and relatively inexpensive. • Improvements such as dual-channel technology and doubledatarate (DDR)have increased SDRAM speed.
How is ROM different from RAM? • ROM (read-only memory) is a type of memory circuitry that holds the computer’s startup routine. • ROM is housed in a single integrated circuit which is plugged into the system board. • Whereas RAM is temporary and volatile, ROM is permanent and nonvolatile.
How is ROM different from RAM? • ROM holds “hard-wired” instructions that are a permanent part of the circuitry and remain in place even when the computer power is turned off. • The instructions in ROM are permanent, and the only way to change them is to replace the ROM chip.
If a computer has RAM, why does it need ROM too? • ROM contains a small set of instructions called the ROM BIOS (basic input/output system). • These instructions tell the computer how to access the hard disk, find the operating system, and loadit into RAM. • After loading the operating system, the computer can accept input, display output, run software, and access data.
Where does a computer store its basic hardware settings? • A computer, to operate correctly, must have some information about storage, memory, and display configurations. • To store this information, the computer needs a type of memory that’s more permanent than RAM, but less permanent than ROM. • EEPROM(electrically erasable programmable read-only memory) is a non-volatile chip that requires no power to hold data. • When the configuration of a computer system is changed, as by adding RAM, the data in EEPROM must be updated. • Some operating systems recognize such changes and automatically perform the update.