the storage of sparse incidence matrices. This data structure is built

into a set of labeled COMMON areas called "SIM COMMON." At any time

only one sparse incidence matrix (SIM) can occupt this common area.

 Quite often during the analysis performed by the GENIE system it

becomes necessary to temporarily stop working with one SIM and start

working with another, without losing the data in the first. Since all

routines operate on SIM's in the SIM COMMON area, it is necessary to

move the first SIM out of common and at some later time restore it to

the common area. This type of movement is not restricted to SIM's and

is desirable for many different data structures. It became necessary to

design a general purpose memory system, easily assessible to any of a

variety of routines which need to store data in a relocatable fashion,

so that the data can be sestored to the appropriate data structure when

required.

 The memory system which accomplishes this is itself a labeled

COMMON area called, appropriately enough, "MEMORY." The memory system

consists of two major storage areas, or vectors, the larger being

"MEMORY" and the smaller being "MEMDIR." MEMORY is the area of core

into which data to be saved are moved. It is a long vector (in the

first version 5,000 words) and could conceivably be much longer. MEMDIR

is a directory to the vector MEMORY which contains all of the informa-

tion necessary to relocate a data item stored in MEMORY. A third major

storage area associated with the memory system is a random access mass

memory data set onto which data from MEMORY are written should MEMORY

ever not have enough space available to store a data item. It should be

noted that many different data items will in general be stored in MEMORY

at the same time, and that if enough are stored MEMORY will become full.