IOPL

The IOPL (I/O Privilege level) flag is a flag found on all IA-32 compatible x86 CPUs. It occupies bits 12 and 13 in the FLAGS register. In protected mode and long mode, it shows the I/O privilege level of the current program or task. The CPL (Current Privilege Level) (CPL0, CPL1, CPL2, CPL3) of the task or program must be less than or equal to the IOPL in order for the task or program to access I/O ports.

The IOPL can be changed using POPF(D) and IRET(D) only when the current privilege level is Ring 0.

Besides IOPL, the I/O Port Permissions in the TSS also take part in determining the ability of a task to access an I/O port.

See also

CONFIG.SYS

CONFIG.SYS is the primary configuration file for the DOS and OS/2 operating systems. It is a special ASCII text file that contains user-accessible setup or configuration directives evaluated by the operating system during boot. CONFIG.SYS was introduced with DOS 2.0.

Usage

The directives in this file configure DOS for use with devices and applications in the system. The CONFIG.SYS directives also set up the memory managers in the system. After processing the CONFIG.SYS file, DOS proceeds to load and execute the command shell specified in the SHELL line of CONFIG.SYS, or COMMAND.COM if there is no such line. The command shell in turn is responsible for processing the AUTOEXEC.BAT file.

CONFIG.SYS is composed mostly of name=value directives which look like variable assignments. In fact, these will either define some tunable parameters often resulting in reservation of memory, or load files, mostly device drivers and TSRs, into memory.

In DOS, CONFIG.SYS is located in the root directory of the drive from which the system was booted.