30-06-2012, 12:01 PM
RISC and CISC
RISC and CISC.pptx (Size: 56.67 KB / Downloads: 50)
Instruction set design
Earlier computer had small and simple instructions sets to minimize hardware
But as hardware become cheaper instructions no. and complexity increased
Processors started supporting variety of data type and large no. of addressing mode
Two philosophy for instruction set design
RISC – Reduced instruction set computers
CISC – complex instruction set computers
CISC
Memory was expensive
bigger program->more storage->more money
Hence needed to reduce the number of instructions per program
Number of instructions are reduced by having multiple operations within a single instruction
To ease development of system software's
Hardware handles the complexity
CISC Characteristics
A large no. of instructions
Variable length Instruction format
A large no. of addressing modes
Fetch-decode execute time is unpredictable
Load and store from memory incorporated in instructions
Multi memory cycle instructions
Some instruction handle specialized tasks
Used infrequently
RISC
Original idea to reduce the ISA (instruction set architecture).
* Provide minimal set of Simple instructions that could carry out all essential operations
Complexity is removed from ISA and is moved into the domain of the assembly programmer/compiler
RISC Characteristics
Relatively few instructions
Relatively few addressing modes
Memory access limited to load and store
instructions
All operations can be done within the registers of
CPU
Fixed-length, easily decoded instruction format
Single-cycle instruction format
Hardwired rather than Microprogrammed
Control
RISC and CISC.pptx (Size: 56.67 KB / Downloads: 50)
Instruction set design
Earlier computer had small and simple instructions sets to minimize hardware
But as hardware become cheaper instructions no. and complexity increased
Processors started supporting variety of data type and large no. of addressing mode
Two philosophy for instruction set design
RISC – Reduced instruction set computers
CISC – complex instruction set computers
CISC
Memory was expensive
bigger program->more storage->more money
Hence needed to reduce the number of instructions per program
Number of instructions are reduced by having multiple operations within a single instruction
To ease development of system software's
Hardware handles the complexity
CISC Characteristics
A large no. of instructions
Variable length Instruction format
A large no. of addressing modes
Fetch-decode execute time is unpredictable
Load and store from memory incorporated in instructions
Multi memory cycle instructions
Some instruction handle specialized tasks
Used infrequently
RISC
Original idea to reduce the ISA (instruction set architecture).
* Provide minimal set of Simple instructions that could carry out all essential operations
Complexity is removed from ISA and is moved into the domain of the assembly programmer/compiler
RISC Characteristics
Relatively few instructions
Relatively few addressing modes
Memory access limited to load and store
instructions
All operations can be done within the registers of
CPU
Fixed-length, easily decoded instruction format
Single-cycle instruction format
Hardwired rather than Microprogrammed
Control