The IPL function in the System/360 and its successors prior to IBM Z, and its compatibles such as Amdahl's, reads 24 bytes from an operator-specified device into main storage starting at real address zero. The second and third groups of eight bytes are treated as Channel Command Words (CCWs) to continue loading the startup program (the first CCW is always simulated by the CPU and consists of a Read IPL command, .mw-parser-output .monospacedfont-family:monospace,monospace02h, with command chaining and suppress incorrect length indication being enforced). When the I/O channel commands are complete, the first group of eight bytes is then loaded into the processor's Program Status Word (PSW) and the startup program begins execution at the location designated by that PSW.[22] The IPL device is usually a disk drive, hence the special significance of the 02h read-type command, but exactly the same procedure is also used to IPL from other input-type devices, such as tape drives, or even card readers, in a device-independent manner, allowing, for example, the installation of an operating system on a brand-new computer from an OS initial distribution magnetic tape. For disk controllers, the 02h command also causes the selected device to seek to cylinder 0000h, head 0000h, simulating a Seek cylinder and head command, 07h, and to search for record 01h, simulating a Search ID Equal command, 31h; seeks and searches are not simulated by tape and card controllers, as for these device classes a Read IPL command is simply a sequential read command.