4 Central processor complex I/O  structure This chapter describes the I/O system structure and connectivity options that are available on  the IBM z15 servers. Note:  Throughout this chapter,  z15  refers to IBM z15 Model T01 (Machine Type 8561). This chapter includes the following topics: GLYPH<SM590000> 4.1, “Introduction to I/O infrastructure” on page 156 GLYPH<SM590000> 4.2, “I/O system overview” on page 158 GLYPH<SM590000> 4.3, “PCIe+ I/O drawer” on page 160 GLYPH<SM590000> 4.4, “CPC drawer fanouts” on page 163 GLYPH<SM590000> 4.5, “I/O features” on page 166 GLYPH<SM590000> 4.6, “Connectivity” on page 169 GLYPH<SM590000> 4.7, “Cryptographic functions” on page 201 GLYPH<SM590000> 4.8, “Integrated Firmware Processor” on page 203 155 ' Copyright IBM Corp. 2 020. All rights reserved.