34 ;;Quote: interface design is the most important part of system design; should be simple, complete, and allow an efficient implementation

34 ;;Quote: an interface defines a small programming language of objects and operations; does not need a syntactic definition

34 ;;Quote: perfection is reached when there is nothing to take away

35 ;;Quote: an interface should capture the minimum essentials of an abstraction, without generalization

35 ;;Quote: an interface is a contract to deliver a certain amount of service and functionality

35 ;;Quote: while clients of an interface depend on an efficient implementation; the costs are seldom documented

35 ;;Quote: everything should be as simple as possible but no simpler

36 ;;Quote: an interface should be fast; basic operations should execute quickly, otherwise everyone pays for a powerful by slow operation

37 ;;Quote: an interface shouldn't hide power; abstractions should not bury the power of lower abstraction levels

37+;;Quote: an abstraction should conceal undesirable properties without hiding desirable ones

37 ;;Quote: procedure arguments increases the flexibility of an interface; e.g., a procedure instead of a mini-language for testing some property

37 ;;Quote: Spy allows a user to patch the supervisor program; no wild branches, no loops, short, stores only into statistic memory

37 ;;Quote: an interface should solve only one problem and let client routines do the rest; e.g., a parser calls client-supplied semantic routines

38 ;;Quote: constant tension between improving a design and providing stability and continuity

38 ;;Quote: if change an interface, should provide backward compatibility by implementing the old interface

38 ;;Quote: world-swap debugger writes the memory image to disk and swaps in the debugger; clumsy but almost no dependence on the target system

40 ;;Quote: handle normal and worst case separately; the normal case is fast and the worst case makes progress

40 ;;Quote: if a count reaches its limit, reduce by half, increment an overflow count in a hashed table, and set a flag; reverse for decrementing

41 ;;Quote: if in doubt, split resources instead of sharing them; faster allocation and access, more predictable

41 ;;Quote: interpret by dynamically translating a compact, flexible or mnemonic representation into a fast representation and caching the result

43 ;;Quote: use hints to speed up normal execution; like cache but may be wrong and doesn't need associative lookup

43 ;;Quote: for Alto and Pilot, a file's leader page defined the file's directory and string name; the actual directory entry was just a hint

43 ;;Quote: the bit table for free disk pages is a hint, verified against the label of the free page

43 ;;Quote: on the Ethernet, lack of a carrier is a hint that a packet can be sent

44 ;;Quote: often better to use a straightforward, brute force solution that is easily analyzed, than a poorly understood one

44 ;;Quote: compute in the background when possible; rapid response to requests, and load balancing

44 ;;Quote: use batch processing if possible; more efficient and simpler error recovery

44 ;;Quote: a general-purpose system can not optimize the use of resources; too easy to overload the system and degrade service by thrashing

44 ;;Quote: in a paging system, the only important thing is to avoid thrashing; otherwise spend all of the time waiting for the disk

45 ;;Quote: few parameters work in processor scheduling; interactive vs. batch, foreground vs. background, fixed share of cycles per job, unused cycles wasted

45 ;;Quote: shed load to control demand rather than allowing the system to become overloaded

45 ;;Quote: reliability requires simplicity

45 ;;Quote: while end-to-end error recovery is sufficient, it requires a cheap test for success and may cause severe performance problems under heavy load

46 ;;Quote: for reliability, log all updates to an object; since append-only, non-volatility is cheap

46 ;;Quote: while objects are not immutable, a version is immutable; change version whenever change object

46 ;;Quote: version id by [object id, number of updates]; then replaying the specified number of log entries yields the desired version

47 ;;Quote: all actions should be atomic or restartable; i.e., use transactions