6.1.9+Outline+how+an+operating+system+hides+the+complexity+of+the+hardware+from+users+and+applications.

Students should be aware of a range of examples where operating systems virtualize real devices, such as drive letters, virtual memory, input devices, the Java virtual machine. INT Issue of localization causing compatibility problems between systems in different countries.

Users and applications do not see the hardware directly, but view it through the operating system. Applications and users view the hardware through the OS.This is used to hide certain hardware details from users and applications. Due to this abstraction, users cannot see changes in the hardware. For example, interaction with 3D graphics hardware can be controlled by the operating system. Another way that abstraction can be used is to make related devices appear the same from the user point of view. For example, hard disks, floppy disks, CD-ROMs, and even tape are all very different media, but in many operating systems they appear the same to the user.

**Drive letters** Alternatively referred to as a device letter, a drive letter is a single alphabetic character A through Z that has been assigned to a physical drive or drive [|partition]  in the computer. For example, a computer with a 3 1/2" [|floppy diskette drive]  has a drive letter of A: assigned to the drive. All computers with a hard drive will always have that default [|hard drive]  assigned to a C: drive letter and the CD-ROM or other disc drive is the last drive letter (e.g. D:).



= The Java Virtual Machine (JVM) = A Java virtual machine (JVM), an implementation of the Java Virtual Machine Specification, interprets compiled Java binary code (called bytecode) for a computer's processor (or "hardware platform") so that it can perform a Java program's instructions.