Hardware Reference
In-Depth Information
Digital storage oscilloscope (DSO)
A Digital storage oscilloscope (or DSO)
combines elements of both hardware and software. These must work together
to provide all the functionality of a conventional DSO but also those of a spec-
trum analyzer, data logger, digital frequency meter, and voltmeter. In many
cases a modern DSO will be able to replace several items of conventional test
equipment. Switching between these instruments is usually quick and easy, and
in most cases each instrument is able to have its dedicated window on the PC
display.
Direct memory access
A method of fast data transfer in which data moves
between a peripheral device (e.g. a hard disk) and main memory without direct
control of the processor.
Directory
A catalogue of disk files (containing such information as filename,
size, attributes, and date/time of creation). The directory is stored on the disk
and updated whenever a file is amended, created, or deleted. A directory entry
usually comprises 32 bytes for each file.
DIP switch
A miniature PCB mounted switch that allows configuration
options (such as IRQ or DMA settings) to be selected.
Disk operating system (DOS)
A group of programs which provide a low-
level interface with the system hardware (particularly disk I/O). Routines
contained within system resident portions of the operating system may be used
by the programmer. Other programs provided as part of the system include
those used for formatting disks, copying files, etc.
Double word
A data value which comprises a group of 32 bits (or two words).
See also
Wo r d
.
DRAM
DRAM (or Dynamic Random Access Memory) refers to the semicon-
ductor read/write memory of a PC. DRAM requires periodic 'refreshing' and
therefore tends not to offer the highest speeds required of specialized memories
(such as cache memory). DRAM is, however, relatively inexpensive.
Driver
In a software context, a driver is a software routine which provides a
means of interfacing a specialized hardware device (see also
Device driver
). In
a hardware context, a driver is an electrical circuit which provides an electrical
interface between an output port and an output transducer. A driver invariably
provides power gain (i.e. current gain and/or voltage gain), see also
Amplifier
.
EIDE
EIDE (or 'Enhanced Integrated Drive Electronics') is the most widely
used interface for connecting hard disk drives to a PC. Most motherboards now
incorporate an on-board EIDE controller rather than having to make use of an
adapter card. This allows one or two hard disk drives to be connected directly
to the motherboard.
Expanded memory (EMS memory)
Memory which is additional to the con-
ventional 'base' memory available within the system. This memory is 'paged'
into the base memory space whenever it is accessed. The EMS specification
uses four contiguous 16 K pages of physical memory (64 K total) to access up
to 32 M of expanded memory space. See also
Expanded memory manager
.
