Variable length instruction vs. fixed length

With fixed-length fields, you would need to define each field to be long enough to hold the longest name. This would be a waste of space for records that had short names. With variable-length fields, the NAME field in each record would be just long enough to hold its data. The opposite of variable length is fixed length. Vangie Beal A variable-length field is one whose length can be different in each record, depending on what data is stored in the field. The terms fixed length and variable length can also refer to the entire record. A fixed-length record is one in which every field has a fixed length. A variable-length record has at least one variable-length field. Vangie Beal The instruction thus fed to the system can be of two types: fixed length instructions and variable length instructions. Advantages of fixed-length instructions are given below: • It simplifies the process of instruction fetching. • The instruction pointer is incremented by a constant amount. • The length of the instruction is known in Complex and variable-length instructions A small number of fixed-length instructions A large number of instructions Limited addressing modes Compound addressing modes Important applications are Security systems, Home automation. Important applications are : Smartphones, PDAs. Varying formats (16-64 bits for each instruction). fixed (32-bit) format In coding theory a variable-length code is a code which maps source symbols to a variable number of bits. Variable-length codes can allow sources to be compressed and decompressed with zero error ( lossless data compression) and still be read back symbol by symbol. Does an architecture that has fixed-length instructions necessarily have only one instruction format? If multiple formats are possible given a single instruction size in bits, explain how they could be implemented; if not, explain why this is not possible. fixed vs variable length instructions, memory-register or load-store (d) Advantage of Does the instruction length (the amount of bits) affect the amount of a smaller instruction-length allows more instructions per byte. Still, using variable-length for greater density or extendability might counter that advantage due to complexity. IA-64 has a fixed 128 bit instruction length and is unrelated to x86, other than being Solution for Is it better or worse to have fixed-length instructions vs instructions that are variable-length by nature? It's difficult to determine which is… A RISC instruction set normally has a fixed instruction length (often 4 bytes = 32 bits), whereas a typical CISC instruction set may have instructions of widely varying length (1 to 15 bytes for x86). Fixed-length instructions are less complicated to handle than variable-length instructions for several reasons (not having to check whether an Variable-length codes (VLCs) are widely used in media transmission. Compared to fixed-length codes (FLCs), VLCs can represent the same message with a lower bit rate, thus having a better Variable-length vs. fixed-length instructions 6 Types of ISA Complex instruction set computer (CISC) Many instructions (several hundreds) An instruction takes many cycles to execute Example: Intel Pentium Reduced instruction set computer (RISC) Small set of instructions Simple instructions, each executes in one clock cycle -almost. Variable-length vs. fixed-length instructions 6 Types of IS