DAC (Digital-to-Analog Converter)
A sound card component that converts the digital signals generated by the CPU to an analog electrical signal that can drive the speakers.
DDR SDRAM (Double Data Rate Synchronous Dynamic Random Access Memory)
A standard for SDRAM where data is transferred twice per clock cycle (making the maximum data rate 64x the bus speed in bps). DDR2/ DDR3/DDR4 SDRAM uses lower voltage chips and higher bus speeds.
default mask
In the early days of IP addressing, the network ID was determined automatically from the first octet of the address. When subnet masks were introduced, the "default" masks (255.0.0.0, 255.255.0.0, and 255.255.255.0) that corresponded to treating the first octet as classful were commonly described as "class A", "class B", and "class C" masks. The Internet no longer uses classful addressing but many LANs use the private IP address ranges and the default masks.
developer unit
Assembly that applies toner to areas of the photoconductor where charge has been removed by the laser. The main components are a toner hopper, transfer roller, waste toner hopper, a screw or blade to stir the toner, and a doctor blade to ensure the correct level of toner on the developer roller.
DHCP Server (Dynamic Host Configuration Protocol server)
A networking service that allows a client to request an appropriate IP configuration from a server. The server is configured with a range of addresses to lease. Hosts can be allocated an IP address dynamically or be assigned a reserved IP address, based on the host's MAC address.
The server can also provide other configuration information, such as the location of DNS servers. DHCP utilizes UDP ports 67 and 68. It is important to monitor the network to ensure that only valid DHCP servers are running on the network.
digitizer
As part of a touchscreen assembly, the digitizer is a touch-sensitive glass panel covering the LCD. The panel converts touch events to digital signals that can be interpreted as different types of input.
DIMM (Dual In-line Memory Module)
The standard packaging for system memory.
There are different pin configurations for different RAM types (DDR SDRAM [184], DDR2/3 SDRAM [240], and DDR4 SDRAM [288]).
disk striping
A disk array access pattern where data is written in stripes to two or more disks sequentially, improving performance. Note that a RAID 0 striped volume provides no redundancy, and if any of the physical disks in the set fails, the whole volume will be lost.
disk thrashing [evidenced by continuous LED blinking over an extended period of time]
A state in which the main memory is filled up, pages are swapped in and out of virtual memory—which needs to be written to the hard disk—in rapid succession, leading to possible early drive failure.
distinguished name
A unique identifier for any given resource within the LDAP (Lightweight Directory Access Protocol) directory.
DLP (video) -Digital Light Processing
Mirror-based projector technology developed by Texas Instruments.
DMZ (Demilitarized Zone)
A private network connected to the Internet must be protected against intrusion from the Internet. However, certain services may need to be made publicly accessible from the Internet (web and email, for instance).
One solution is to put such servers in a DMZ. The idea of a DMZ is that traffic cannot pass through it. If communication is required between hosts on either side of a DMZ, a host within the DMZ acts as a proxy. It takes the request and checks it. If the request is valid, it re-transmits it to the destination. External hosts have no idea about what (if anything) is behind the DMZ. A DMZ is implemented using either two firewalls (screened subnet) or a single three-legged firewall (one with three network ports).
DNS (Domain Name System)
A network service that provides names to IP address mapping services on the Internet and large intranets. DNS name servers host the database for domains for which they are authoritative. Root servers hold details of the top-level domains. DNS resolvers perform queries or lookups to service client requests. The DNS protocol utilizes TCP/UDP port 53.
docking station
A sophisticated type of port replicator designed to provide additional ports (such as network or USB) and functionality (such as expansion slots and drives) to a portable computer when used at a desk.
Not to be confused with a PORT REPLICATOR
DSL (Digital Subscriber Line)
A technology for transferring data over voice-grade telephone lines. DSL uses the higher frequencies available in a copper telephone line as a communications channel. The use of a filter prevents this from contaminating voice traffic with noise. There are various "flavors" of DSL, notably S(ymmetric)DSL, A(symmetric)DSL, and V(ery HIgh Bit Rate)DSL.
DTLS (Datagram Transport Layer Security)
TLS used with UDP (User Datagram Protocol) applications, such as some VPN solutions.
DVI (Digital Video Interface)
A video adapter designed to replace the VGA port used by CRT monitors. The DVI interface supports digital only or digital and analog signaling.