CMS Storage Layout

Storage layout is determined by the size of the virtual machine relative to the top of the nucleus, which is typically at 20 MB. The location and size of the page allocation table vary according to the size of the virtual machine. In virtual machines larger than 20 MB, the page allocation table is built at the top of virtual storage. In virtual machines smaller than or equal to 20 MB, the page allocation table extends down from whichever is less: the bottom of the nucleus or the top of virtual storage.

Figure 1 and Figure 2 show sample CMS storage layouts for virtual machines whose sizes are less than or equal to the top of the nucleus.

Figure 3 shows a sample CMS storage layout for a virtual machine that extends beyond the top of the nucleus. Free storage starts above the transient program area and extends up to the limit of the virtual machine size (excluding any storage used by CMS).

For more information on the size and location of the page allocation table, see the z/VM: CMS Planning and Administration.
Figure 1. Storage Configuration for a Virtual Machine Less Than 15 MB. The top of the virtual machine is less than the start of the CMS nucleus.
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Figure 2. Storage Configuration for a Virtual Machine Equal to 20 MB
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Figure 3. Storage Configuration for a Virtual Machine Greater than 20 MB
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