1)Discussion on previous homework for ISA(instruction set architecture)

The trend of moving to RISC is driven by ‘economic’ factor. The idea is trying to reduce the fetching time from memory by doing simple instruction. This can be understood by analyzing the various number of addresses used in each instruction; included in the CISC are three-address, two-address, single-address and general-register, and the stack computing is included in the RISC group (see one-page handout for analysis example). In general, fewer lines are needed in symbolic language for CISC, but each instruction is more complex and involved more memory traffic. RISC uses register instead of memory reference, and therefore requires more in execution size but less in total memory traffic.

Stack machine, one of oldest operation structure, has simple instruction like RISC, but it is also small in execution size. Since RISC has gained popularity, stack machine has good potential to come back.

2) Definition and Inter-relationship of the non-functional global properties:

Dependability, Safety and Security, and how they influence the system Survivability. Intercepting circles can best depict the domain of what each of these properties can do. The new area common to all three properties (like survivability) is being developed based on the common technology they possess instead of the common problem they can solve.

Dependability - similar to survivability and security (often this definition depends on each individual’s expertise.)

Safety - a property of the system which can justify the service it delivers, it is built on error (error handling, error primness, and error tolerance) and fault (fault and fault tolerance). The terms fail safe and fail soft are used to describe in the event of failure how a system can retreat into safe operating mode or to provide partial service. Strategies like recovery or restoration and robustness are essential elements in safety, because they can ‘keep the system running and not terminate’.

Security - Confidentiality, Integrity and Availability.

Survivability - The basic elements are Availability, Integrity, and confidentiality (notice the reversed order of them from security). The most important factor to sustain survivability is ‘diversity’. Survivability is by itself a new subject area, since all other techniques were separately developed and all were before the time of Internet or Unbounded Network. The basic driving force of moving toward using Internet is ‘economic’.