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index bfc939c..0b7ef92 100644
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@@ -41,9 +41,29 @@ symbol | Symbol assembler and command files
 tests  | A magtape test, so far
 tools  | Possibly useful tools
 
-
-
-
+## PAL and Program Identification
+
+The SDS/Xerox Program Availability List (PAL) manual contains a list of all available Xerox software products, user programs and programming manuals. The systems that control the distribution and ensure the updating of the items listed are also described. 
+
+All available Xerox (SDS) software is identified by a unique six-digit number which is referred to as a program catalog number. This catalog number may encompass a series of programs if these programs are ordinarily ordered as a group (e.g., Sigma 2/3 Numerical Subroutine Package, Catalog No. 705546). When this group is made available as a package, only a single "cover number" is used to identify it.
+Every program catalog number has a two-digit number appended to it which is referred to as a program element. It is in the form "xy" where x usually refers to the form (source, binary, etc.) and y usually refers to the media (printed, magnetic tape, etc.) of the program. For example, a "-11" is a printed description of the program and a "-84" is absolute binary cards. The descriptions of these di:gits are summarized below:
+
+First Digit Meaning | Second Digit Meaning
+---|---
+0 Miscellaneous | 0 Miscellaneous
+1 Description | 1 Printed
+2 Relocatable Binary | 2 7 level paper tape
+3 Source | 3 8 level paper tape
+4 Compressed | 4 Cards
+5 Listing | 5 7 track magnetic tape
+6 Update | 6 9 track magnetic tape
+7 Miscellaneous | 7 Disk pack
+8 Absolute Binary | 8 Miscellaneous
+9 Miscellaneous | 9 Miscellaneous
+
+NOTE:
+There are two permanently assigned program elements with the first digit zero. The designation of -·01 is assigned to technical bulletins and a -02 is assigned to an unpublished technical document.
+ Not all of the possible elements are available for each program. Programs are usually distributed on the type of media that would be most suitable for the potential users. Refer to the Status List section for the available elements for each program. If an element is not listed, it may be ordered only on a Field Request; see Special Requests below.