applications, such as DB2 Version 8 and above, now require and exploit 64-bit addressing. IBM markets z/OS as its flagship operating system, suited for continuous, high-volume operation with high security and stability. z/OS is available under standard license pricing and via IBM Z New Application License Charges (zNALC) and "IBM Z Solution Edition", two lower-priced offerings aimed at supporting newer applications ("new workloads"). U.S. standard commercial z/OS pricing starts at about US$125 per month, including support, for the smallest zNALC installation running the base z/OS product plus a typical set of optional z/OS features. z/OS introduced Variable Workload License Charges (VWLC) and Entry Workload License Charges (EWLC) which are sub-capacity billing options. VWLC and EWLC customers only pay for peak monthly z/OS usage, not for full machine capacity as with the previous OS/390 operating system. VWLC and EWLC are also available for most IBM software products running on z/OS, and their peaks are separately calculated but can never exceed the z/OS peak. To be eligible for sub-capacity licensing, a z/OS customer must be running in 64-bit mode (which requires z/Architecture hardware), must have eliminated OS/390 from the system, and must e-mail IBM monthly sub-capacity reports. Sub-capacity billing substantially reduces software charges for most IBM mainframe customers. Advanced Workload License Charges (AWLC) is the successor to VWLC on mainframe models starting with the zEnterprise 196, and EAWLC is an option on zEnterprise 114 models. AWLC and EAWLC offer further sub-capacity discounts. Other features 64-bit memory support z/OS supports 64-bit addresses for both virtual and real addresses. Within each address space, z/OS typically permits the placement of only data, not code, above the 2 GB "bar". z/OS enforces this distinction primarily for performance reasons. There are no architectural impediments to allowing more than 2 GB of application code per address space. IBM has started to allow Java code running on z/OS to execute above the 2 GB bar, again for performance reasons. Starting with z/OS version 2 release 3, code may be placed and executed above the 2 GB "bar". However, very few z/OS services may be invoked from above the "bar". Memory is obtained as "Large Memory Objects" in multiples of 1 MB (with the expectation that applications and middleware will manage memory allocation within these large pieces). There are three types of large memory objects: Unshared – where only the creating address space can access the memory. Shared – where