Other GPSS versions
The main difference between aGPSS and these two commercial versions is
that these versions cater to an existing commercial customer base, often
requiring sophisticated features. They hence aim at being upwards
compatible with earlier GPSS versions, in fact going back to old IBM
versions from 1965. This has lead to these versions having many more
block types. Thus while aGPSS has only 21 block types, GPSS/H has some 70
block types. Many of these block types in GPSS/H do roughly the same kind
of job. Thus LET in aGPSS does the same job as
aGPSS on the other hand does not have to bother about an old
commercial customer base. Instead it has been continuously simplified
based on student feedback. When many students have found something
difficult to learn, we have changed the syntax. As an example, if you go
BYE when then queue at Joe is already 4, we write in
IF Q$Joe=4,BYE, while one in GPSS/H has to
TEST NE Q$JoeQ,4,BYE.
Because of simplifications like this, aGPSS is much easier to learn than other GPSS versions. With aGPSS one has been able to cover the same material in 10 hours that required 22 hours when using a commercial GPSS version.
Yet, aGPSS is almost as powerful as these other GPSS versions. For example, all of Tom Schriber's famous Red book case studies and 99 percent of other GPSS textbook programs have been rewritten with the same amount of code in aGPSS. Hence, aGPSS has definitely proved to be powerful enough for student projects.
With aGPSS allowing for a one-to-one relationship between the graphical block diagram and the computer code, it has proved easy for students to proceed from aGPSS to both text based simulation languages like SLX and to animation based simulation systems like ARENA.
Further information on the history of GPSS and on different GPSS versions is provided here.