This amount of memory will vary for different platforms and how the system is used. For example, UNIX file systems do more file buffering than UNIX raw partitions, so the operating system has a higher memory requirement. As a minimum, you can assume that UNIX systems use 60MB or more, while Windows systems use 30MB or more.
In addition, other applications that run in conjunction with Sybase IQ (such as query tools) have their own memory needs. See your application and operating system documentation for information on their memory requirements.