The superscalar processor implements third-generation Simultaneous Multi-Threading  (SMT)$^{4}$. It also implements redesigned OoO, augmented caches and translation lookaside  buffer (TLB), optimized pipeline, and better branch prediction.  Also featured is an expanded instruction set with Vector Packed Decimal Facility, Guarded  Storage Facility, Vector Facility enhancements, Semaphore Assist Facility, Order Preserving  Compression, Entropy Encoding for Co-processor Compression for better performance in  several different areas, and the IBM Integrated Accelerator for zEnterprise Data Compression  (on-chip compression accelerator). Depending on the model, the z15 server can support 512 GB - 40 TB of usable memory, with  up to 8 TB of usable memory per CPC drawer. In addition, a fixed amount of 256 GB is  reserved for the hardware system area (HSA) and is not part of customer-purchased memory.  Memory is implemented as a redundant array of independent memory (RAIM) and uses extra  physical memory as spare memory. The RAIM function accounts for 20% of the physical  installed memory in each CPC drawer. New with z15, Virtual Flash Memory (VFM) feature is offered from the main memory capacity  in 0.5 TB units (versus 1.5 TB per feature on z14) increasing granularity for the feature. VFM  provides much simpler management and better performance by eliminating the I/O to the  adapters in the PCIe+ I/O drawers. VFM does not require any application changes when  moving from IBM zFlash Express (previously available on z13fi and zEC12). The z15 server provides increased processing and enhanced I/O capabilities over its  predecessor, the z14 system. This capacity is achieved by increasing the performance of the  individual PUs and the number of PUs per system, redesigning the system cache, increasing  the amount of memory, and introducing new I/O technologies.  The increased performance and the total system capacity available (with potential energy  savings) allows consolidation of diverse applications on a single platform with significant  financial savings. The introduction of new technologies and an expanded and enhanced  instruction set ensure that the z15 server is a high-performance, reliable, and rich-security  platform. The z15 server is designed to maximize the use of resources and allows you to  integrate and consolidate applications and data across the enterprise IT infrastructure. z15 server is offered in one model (T01) with five maximum processor features, with 1 - 190  configurable PUs. The processor features Max34, Max71, Max108, and Max145 have one,  two, three, respective four CPC drawers with 41 active PUs per CPC drawer. The  high-capacity feature (Max190) has five processor (CPC) drawers with 43 PUs per drawer.  The z15 T01 feature Max190 is estimated to provide up to 25% more total system capacity  than the z14 Model M05, with the same amount of memory and power requirements. With up  to 40 TB of main storage and enhanced SMT, the performance of the z15 processors deliver  considerable improvement. Uniprocessor performance also increased significantly. A z15  Model 701 offers average performance improvements of up to 14%$^{5}$ over the z14 Model 701. The Integrated Facility for Linux (IFL) and IBM Z Integrated Information Processor (zIIP)  processor units on the z15 server can be configured to run two simultaneous threads per  clock cycle in a single processor (SMT). This feature increases the capacity of these  processors with 25% in average$^{5}$ over processors that are running single thread. SMT is also  enabled by default on System Assist Processors (SAPs). Chapter 1. Introduction  5 4 Simultaneous multithreading is two threads per core. 5 Observed performance increases vary depending on the workload types. 1.2.2 Capacity and performance