If a block larger than 30 doublewords is returned via it is merged appropriately into the regular free storage chain. Then, unless
the block was returned by DMKPRETR (see "Initialization") a check is made to see if the area given back (after all merging has been done) is
a page frame within the dynamic paging area. If so, returns it
to the dynamic paging area for subsequent use. !ll.Q£at!on The number of page frames allocated to free storage depends upon:
1. The real machine storage size
2. The RKSIZE operand specified in the SYSCOR macro at system generation time
3 The FREE operand in the SYSCOR macro
The storage size used DY is the smaller of the real machine storage size and the RKSIZE value.
If the PREE operand was not included in the SYSCOR macro statement for DKKSYS, the default number of fixed free storage pages allocated at IPL time for the first 256K of storage is 3 and 1 page for each 64K
thereafter, not including V=R size, if any.
If the FREE operand was included in the SYSCOR macro statement for DMKSYS, that value is the number of fixed free storage page frames allocated at IPL time. If those pages represent an amount of free
storage greater than 25% of the VK/370 storage size (not including V=R size, if any) the default allocation is used. CP INITIALIZATION System initialization starts when the operator selects the DASD device
address of the CP system residence volume (SYSRES) and presses the IPt button. The Systea/370 hardware reads 24 bytes from record 1 of
cylinder 0 on SYSRES into location 0 of main storage. This record
consists of an initial PSW and a channel program. The channel prograa
reads the module DMKCKP into location 1'800' and gives it control. DKKCKP checks location CPID in module DMKPSA. If CPID contains the value CPCP or WARM, DMKCKP saves the spool file
control blocks, system log messages, accounting information, status of
spool devices, spool hold queue blocks, and spool record allocation
blocks and writes them on the warm start cylinders. If CPID contains
the value CPCP, DKKCKP loads a disabled wait state code 1'008'. If location CPID does not contain the value CPCP, DMKCKP nov loads DKKSAV and passes control to it at entry point DMKSAVRS. reloads
a page image copy of the CP nucleus into real storage starting at page O. When DKKSAV is finished, control is transferred to performs the main initialization function. This includes calling DKKiRK to retrieve the information stored on the warm start cylinder. This
also includes calling DKKCKS to initialize the dynamic checkpoint
cylinders and to checkpoint the current status of the spool file system. When DMKCPI has finished, it passes control to loads
a wait state PSi to wait for work. See "CP Initialization for the
Attached Processor" for additional 1-122 IBM VM/370 System Logic and Problem Deteraination--Voluae 1

INITIALIZATION AND TERMINATION
After CP has been initialized, DMKCPVEN enables the communication lines
in response to the ENABLE command. Then an individual virtual machine
is attached to the system, using the following steps:
1. When the CP receives the initial interrupt from a terminal on an
enabled line (normally initiated by a user dialing in On a
data-set), the DMKCNSIN routine is entered. DMKCNSIN determines
the terminal device type, stores this information in the terminal device bleck, writes the online message and puts the terminal line
in a state to receive an attention interruption.
After the online message has been displayed at the user's terminal,
and he has pressed the ATTENTION key, DMKCNSIN (the console
interruption routine) calls DKKBLDV8 to build a skeleton VMBLOK for
the user. At this time, the userid is LOGONxxx, where xxx is the
terminal real device address, and a flag is set to indicate that
the user has not yet completed the logon process.
Then DMKCNSIN calls which types a single blank at the
terminal, and issues a read to the terminal for the user to enter
his first command (normally LOGON or DIAL).
After the first command has been entered by the user, DMKCNSIN further determines the type of terminal. If the terminal is a
2741, DMKTRMID is called to identify it as either a 2741P
(PTTC/EBCD) or a 2741C (Correspondence) terminal. If successful,
the correct device type and translate tables for input and output
are set; if fiot, flags are set to indicate that the terminal is
not yet identified.
Then control is returned to DMKCFMBK, which determines if the first
command is valid (for example, LOGON, ftSG, or DIAL). If the first
command is not valid, a restart message is given, and the read to
the terminal occurs again for the first command. If the first
command was LOGON (or its abbreviation), DMKLOGON is called to
complete the process of attaching the virtual machine to the
system.
The operations performed by DMKLOGON include the following: • Ensures that the maximum number of virtual machines allowed on
the system is not being exceeded. • Obtains the userid from the command line, and chects for a
possible password and other optional operands. • Checks the userid and password (entered separately if not on the LOGON command line) against entries in CP's directory of users. CP Introduction 1-123