CMPT 295 Lecture Notes - Lecture 5: Readwrite, Program Counter, Von Neumann Architecture
8 Oct 2016
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Machine can operate on 64-bit, but also 32, 16, and 8-bit. Instructions have suffix for size: q (quad), l (long/double), w (word), b (byte) But occasionally ambiguous without e. g. add , (%rax) # ambiguous. Movl %esi, %ecx # puts 0s in upper 32-bits. On very first computers, interpretation was not so general: eniac: penn by eckert and mauchly (1946) Dimensions: 100 ft x 8. 5 ft x several feet wide. Data: 20 x 10-digit registers and 18000 vacuum tubes. Known as the von neumann architecture, but based on a concept by eckert & mauchly. Some hardware allows programmer to label portions of memory as r/w (read/write) only (useful for data) or execute only (useful for code) Maintains the address of the next instruction (%rip read only register) Fetch the next instruction from memory into cpu (load m[pc]) Note: unless the instruction modifies the pc (jump, branch, call, ret) the instructions listed in memory will be executed in sequential order.
