Computer Memory

Computer Memory

• Primary Storage (Main Memory) is a temporary storage area that holds information, application software, and operating system software.
• Increasing memory capacity increases the performance of the system.
• Types of Primary Storage:
  • Registers: part of the CPU, very fast, very limited capacity.
  • Cache Memory: faster than RAM, used to provide intermediate storage between secondary storage and RAM.
  • Random Access Memory (RAM): memory chips on motherboard, general storage of program instructions and data, volatile.
  • Read-only Memory (ROM): chips storing permanent instructions needed by computer, non-volatile.

Characteristics of Main Memory

• Semiconductor memories.
• Known as main memory.
• Usually volatile memory.
• Data is lost in case power is switched off.
• Working memory of the computer.
• Faster than secondary memories.
• A computer cannot run without primary memory.

Secondary Storage

• External memory or non-volatile.
• Contents of secondary memories are first transferred to main memory, and then CPU can access it.
• Slower than main memory.
• For storing data/Information permanently.
• CPU directly does not access these memories instead they are accessed via input-output routines.
• Examples: disk, CD-ROM, DVD, etc.

Characteristics of Secondary Storage

• Magnetic and optical memories.
• Known as backup memory.
• Non-volatile memory.
• Data is permanently stored even if power is switched off.
• Used for storage of data in a computer.
• Computer may run without secondary memory.
• Slower than primary memories.

Computer Evolution

• Different types of computer systems are used in various fields for different applications as per the system performance requirements.
• Different types of computers suitable for the specific types of application.

Computer System Output Unit

• The term “output unit” (output devices) refers to the output data provided by the computer CPU after processing the data inputs.
• This output is then sent to the output devices to provide the desired information to the user.

Central Processing Unit (CPU)

• CPU is considered as the brain of the computer.
• CPU performs all types of data processing operations.
• It stores data, intermediate results, and instructions (program).
• It controls the operation of all parts of the computer.

CPU Components

• Control Unit: Access program instructions, decode instructions, control flow of data throughout system.
• Arithmetic-Logic Unit: Perform computations on data, perform comparisons on data.
• Memory Unit: Stores instructions from programs, stores data to be processed.

CPU Machine Instruction Cycle

• An instruction is fetched from memory/storage unit by the Control Unit.
• The Control Unit decodes the instruction.
• The ALU receives the data and the instruction and executes the computer program.
• The result is stored in primary storage.

Computer Performance

• Measured in part by the number of Machine Instruction Cycles performed per second.
• Factors affecting this performance include:
  • Clock Speed: measures the number of cycles your CPU executes per second, measured in GHz (gigahertz).
  • Cache Memory: stores copies of the data from frequently used main memory.
  • Word Length: Refers to the number of bits processed at a time.
  • Address and Data Bus Width: amount of memory a system can address.