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如被发现从内部的一些片完全未签出该系统的误差和误差追溯到打破有关资源规则导致此类错误。抽象级别的一个额外的好处是的方便，可以修改该系统 ；它的设计被分层的拟议修改的影响都清晰可见。
Appendix--A User‘s View of the S ystem
The user views the system in two ways. First, he must write his
programs; for this he is interested in available data structures and
system procedures. Then he is interested in running and debugging
his programs.
Programs running under Venus use segments for all storage--
procedures, data, and pushdown stacks. Because segments are available
by external name through dictionaries, users can readily share
data and procedures. Users may also synchronize with other users
through queues and semaphores.
A user runs on-line and interactively. He starts up by typing a
command on a teletype and is assigned a virtual machine under the
control of an interactive system procedure called the Loader. The
Loader recognizes many commands; the most important is the "E"
command, which passes control to a specified system, utility, or user
procedure. Important system and utility procedures are the Assembler,
Editor, Tape Requester, and Debugger.
The user submits card decks to be read prior to his run; he may
access all decks through a command to the Loader. The names of
the segments containing the card deck images are entered in a dictionary
associated with the user. The user may read segments from
tape; the names of these segments are also entered into his dictionary
where they may be assembled or edited on command. Binding of
intersegment references occurs on completion of assembly.
The user executes procedures by giving the "E" command.
Execution can occur with or without debugging; no change to the
procedures being run is required. Debugging is handled by an
interactive system procedure which runs before the execution of
every instruction and can be used to stop execution at a specified
"breakpoint." A dialogue with the user then commences in which
the contents of a segment or his work area may be displayed and
modified, a new breakpoint specified, and control returned to the
interrupted procedure or the Loader.
The system also provides interactive interrupt procedures which
run as the result of exceptional conditions, for example, a stack
underflow or overflow. They make use of a subset of the debugging
commands, permitting the user to discover the reason for the error,
restore his data, and return to the Loader.
When the user has finished running he saves his symbolic data
on tape and then informs the Loader, which releases his virtual
machine and destroys his symbolic data. His checked-out programs
may be entered in the system and become accessible to others
through dictionaries.
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原文地址：http://www.cnblogs.com/icecri/p/4495395.html
